STEEL BUMPER SYSTEMS for PASSENGER VEHICLES and LIGHT TRUCKS

Transcription

1 STEEL BUMPER SYSTEMS for PASSENGER VEHICLES and LIGHT TRUCKS Fifth Edition, May 2013 An in-depth report on steel bumper systems, including information on: Material Properties Manufacturing Product Design

2 Steel Bumper Systems for Passenger Cars and Light Trucks Fifth Edition May 2013 Steel Market Development Institute

3 Copyright Steel Market Development Institute This publication is for general information only. The information in it should not be used without first securing competent advice with respect to its suitability for any given application. The publication of the information is not intended as a representation or warranty on the part of Steel Market Development Institute - or any other person named herein - that the information is suitable for any general or particular use or freedom from infringement of any patent or patents. Anyone making use of the information assumes all liability from such use. First Edition, June 1998 First Edition (revision), March 2001 Second Edition, February 2003 Third Edition, June 2006 Fourth Edition, May 2011 Fifth Edition, May 2013

4 Contents Contents Figures Tables Preface Introduction Objective i vi viii ix x xiii 1. Bumper systems and components 1.1 Bumper systems System selection Metal facebar system Plastic fascia and reinforcing beam system Plastic fascia, reinforcing beam and energy absorption system 1.2 Bumper components Fascia Energy absorbers Facebar Reinforcing beam 1.3 Types of Bumper Beams Steel Reimforcing Beams Steel Facebars Plastic Reinforcing Beams Aluminum Reinforcing Beams 2. Steel materials Introduction Typical properties of steel grades for facebars Typical properties of steel grades for brackets, supports, and reinforcing beams FutureSteelVehicle Materials Portfolio for Automotive Applications Elongation versus tensile strength Elongation versus after-fabrication yield strength Elongation versus tensile strength for hot-formed steel Yield strength versus strain rate Sheet steel descriptors SAE J2329 Low-carbon sheet steel Steel grade Types of cold rolled sheet Types of hot rolled sheet i

5 Contents 2.11 SAE J2340 Dent resistant, high-strength and ultra high-strength sheet steel Steel grade Steel type Hot rolled, cold reduced and metallic coated sheet Surface conditions for cold reduced and metallic coated sheet Conditions for hot rolled sheet 2.12 SAE J1562 Zinc and zinc-alloy coated sheet steel Galvanizing processes Types of coatings Coating mass Surface quality Coated sheet thickness Coating designations 2.13 SAE J403 Carbon steel chemical compositions Carbon sheet steel Boron sheet steel 2.14 SAE J405 Wrought stainless steels SAE Specification and ordering descriptions ASTM A463 Aluminized sheet steel Manufacturing processes 3.1 Stamping Stretching Drawing Bending Bending and straightening Forming limits 3.2 Roll forming Hydroforming Hot forming 3-7 ii

6 Contents 3.5 Bumper beam coatings Zinc or zinc-iron coatings Aluminum coating Polishing Chromium coating Conversion coating Electrocoating (ing) Paint coating Autodeposition coating Powder coating 4. Manufacturing considerations 4.1 Forming considerations Guidelines for roll forming high-strength steel Guidelines for roll forming ultra high-strength steel General guidelines for stamping high-strength and ultra high-strength steels Guidelines for hat sections stamped from high-strength or ultra high-strength steels Rules of thumb for high-strength steel stampings 4.2 Welding considerations Steel chemistry High-strength and ultra high-strength steels Welding processes Gas metal arc welding (GMAW) Flux cored arc welding (FCAW) Resistance spot welding (RSW) Resistance projection welding (RPW) Resistance seam welding (RSeW) Resistance projection seam welding (RPSeW) High frequency and induction resistance seam welding (RSeW-HF&I) Upset welding (UW) Friction welding (FRW) Laser beam welding (LBW) Laser beam and plasma arc welding (LBW/PAW) Weldability of bumper materials Ranking of welding processes iii

7 Contents 5. Design concepts 5.1 Sweep (roll formed sections) and depth of draw (stampings) Tailor products Latest benchmark bumper beams Bumper weights, materials and coatings Current steel bumper design - passenger cars Typical bumper design - North American passenger cars Typical bumper design - North American and Europe passenger cars 5.6 Current steel bumper design - pickups, full size vans and sport utilities Auto/Steel Partnership high speed steel bumper design - North American passenger cars Quantech design criteria for high speed steel bumper system Flow Chart for high speed system 5.8 Bumper design for pedestrian impact Impact tests EuroNCAP leg to bumper impacts with a leg-form impactor Government regulations Design approaches Cushioning the impact Supporting the lower limb Design solutions 6. Relevant safety standards in North America and Europe United States National Highway Traffic Safety Administration (49CFR), Part 581 Bumper Standard Requirements Vehicle Pendulum corner impacts Pendulum longitudinal impacts Impacts into a fixed collision barrier 6.2 Canadian Motor Vehicle Safety Regulations Section 615 of Schedule IV Requirements 6.3 United National Economic Commissions for Europe ECE Regulation Requirements Test Vehicle Impact device Longitudinal test procedure Corner test procedure iv

8 Contents 6.4 Insurance Institute for Highway Safety: Bumper Test Protocol (Version VII) Requirements Test vehicles Impact barrier Full-overlap impact Corner impact 6.5 Consumers Union bumper-basher tests Research Council for Automotive Repairs (RCAR) Low-Speed Offset Crash Test Requirements Test vehicle Front impact Rear impact 6.7 Research Council for Automotive Repairs (RCAR) Bumper Test Requirements Bumper barrier Full overlap impact 7. Summary/Conclusions References 8-1 v

9 Figures NORTH AMERICAN BUMPER SYSTEM MARKET SHARE BY UNITS FOR KNOWN SYSTEMS xii 1.1 COMMON BUMPER SYSTEMS COMMON REINFORCING BEAM OSS SECTIONS ELONGATION VERSUS TENSILE STRENGTH INEASE IN YIELD STRENGTH THROUGH WORK HARDENING AND BAKE HARDENING TRANSITIONS IN HF STEEL STRESS VERSUS STRAIN AT DIFFERENT STRAIN RATES FOR DP STRESS VERSUS STRAIN AT DIFFERENT STRAIN RATES FOR DP TYPICAL CIRCLE GRID PATTERN REPRESENTATION OF STRAINS BY ETCHED CIRCLES TYPICAL FORMING LIMIT DIAGRAM a) RULES OF THUMB - SPRINGBACK b) RULES OF THUMB - SPRINGBACK c) RULES OF THUMB - SPRINGBACK RULES OF THUMB - DIE FLANGE STEELS RULES OF THUMB - HAT SECTION RULES OF THUMB - RADIUS SETTING a) RULES OF THUMB - COMBINATION FORM AND FLANGE DIE b) RULES OF THUMB - COMBINATION FORM AND FLANGE DIE RULES OF THUMB - FORMING BEADS RULES OF THUMB - FORMING AN EMBOSS RULES OF THUMB - EDGE SPLITTING RULES OF THUMB - PART DESIGN RULES OF THUMB - DIE CONSTRUCTION RULES OF THUMB - DEVELOPED BLANKS RULES OF THUMB - TRIMMING RULES OF THUMB - DIE SHEAR GAS METAL ARC WELDING (GMAW) FLUX CORED ARC WELDING (FCAW) RESISTANCE SPOT WELDING (RSW) RESISTANCE PROJECTION WELDING (RPW) RESISTANCE SEAM WELDING (RSeW) RESISTANCE PROJECTION SEAM WELDING (RPSeW) HIGH FREQUENCY AND INDUCTION RESISTANCE SEAM WELDING (RSeW-HF&I) UPSET WELDING (UW) FRICTION WELDING (FRW) LASER BEAM WELDING (LBW) HARDNESS IN HEAT-AFFECTED ZONE OF ARC WELDS RESISTANCE SPOT WELDING COMPARISON DEFINITION OF SWEEP DEFINITION OF DEPTH OF DRAW EXAMPLES OF TAILOR WELDED BLANKS ROLL FORMED BEAMS STAMPED FACEBARS HOT-STAMPED BEAMS 5-10 vi

10 Figures 5.7 SHEET HYDROFORMED FACEBAR TYPICAL BUMPER DESIGN FOR PASSENGER CARS AND MINIVANS AUTO/STEEL PARTNERSHIP BUMPER DESIGN FOR HIGH SPEED SYSTEM NORTH AMERICAN PASSENGER CARS EuroNCAP PEDESTRIAN TESTS EuroNCAP LEG FORM IMPACTOR EuroNCAP LEG FORM IMPACT ITERIA (2010) IMPACT PENDULUM PENDULUM SAMPLE IMPACT APPARATUS IMPACT DEVICE IIHS IMPACT BARRIER STEEL BUMPER BARRIER STEEL BACKSTOP OVERLAP FOR FRONT CORNER TEST RCAR FRONT ASH PROCEDURE RCAR REAR ASH PROCEDURE RELEVANT BUMPER ENGAGEMENT BUMPER BARRIER BUMPER BARRIER WITH BACKSTOP AND ENERGY ABSORBER 6-19 vii

11 Tables 2.1 STEEL GRADES FOR POWDER COATED, PAINTED AND CHROME PLATED FACEBARS STEEL GRADES FOR BRACKETS, SUPPORTS AND REINFORCING BEAMS FSV MATERIALS PORTFOLIO FSV MATERIALS PORTFOLIO (continued) SAE J2329 LOW-CARBON COLD ROLLED SHEET MECHANICAL PROPERTIES SAE J2329 LOW-CARBON HOT ROLLED SHEET MECHANICAL PROPERTIES SAE J2329 LOW-CARBON HOT & COLD ROLLED SHEET CHEMICAL COMPOSITION SAE J2340 DENT RESISTANT SHEET STEEL SAE J2340 HIGH-STRENGTH SOLUTION STRENGTHENED AND LOW-ALLOY SHEET STEEL SAE J2340 HIGH-STRENGTH RECOVERY ANNEALED SHEET STEEL SAE J2340 ULTRA HIGH-STRENGTH DUAL PHASE & MARTENSITE SHEET STEEL SAE J1562 COATING MASS FOR GALVANIZED SHEET STEEL SAE J403 CARBON STEEL COMPOSITIONS FOR SHEET SAE J405 CHEMICAL COMPOSITIONS OF WROUGHT STAINLESS STEELS SAE J2340 STEELS AND STRENGTH GRADES SAE J2340 CHEMICAL LIMITS ON UNSPECIFIED ELEMENTS RANKING OF WELDING PROCESSES BY BUMPER MATERIAL SWEEP NUMBERS (CAMBER, X, INCHES) SWEEP NUMBERS (CAMBER, X, MILLIMETERS) LATEST BENCHMARK BUMPER BEAMS ROLL FORMED BUMPER BEAMS MODEL YEAR STAMPED FACEBARS MODEL YEAR HOT FORMED BUMPER BEAMS MODEL YEAR 5-27 viii

12 Preface This publication is the fourth revision of Steel Bumper Systems for Passenger Cars and Light Trucks. It is a living document. As experience in its use is gained, further revisions and expansions will be issued. The standards discussed in this document refer to the editions of the standards as of January Please note in the event that these standards are replaced by newer editions, users of this document are encouraged to investigate the possibility of using the most recent standards. In some cases new vehicles may adopt new edition standards, while current venicles may continue to use the standard edition in place at the time of vehicle development. This publication brings together materials properties, product design information, manufacturing information and cost information. It has been prepared to suit the needs of OEM bumper stylists, bumper engineers and bumper purchasers. It is also intended to suit the needs of the Tier 1 and Tier 2 bumper suppliers and steel industry marketing personnel. This publication was prepared by the Bumper Project Group of the Steel Market Development Institute. The efforts of the following members are acknowledged: AK Steel Corporation AGS Automotive Systems Amino North America Corporation ArcelorMittal USA LLC Benteler Automotive Cosma International Chrysler Group LLC Flat Rock Metal Inc. Flex-N-Gate Ford Motor Company General Motors Company Multimatic Engineering Services Nucor Corporation Shape Corporation ThyssenKrupp Steel USA United States Steel Corporation Steel Market Development Institute May 2013 ix

13 Introduction In 2012, approximately 12.8 million vehicles were sold in North America with 25.6 million bumpers attached. Approximately 83% of these bumpers were steel, approximately 16% were aluminum, and less than 1% were composites. Today there is an increased use of ultra high strength steels (UHSS) which make steel bumpers more mass competitive while also making it more difficult to justify the additional cost of alternative materials. Bumper systems have changed dramatically over the last 30 years. More demanding government regulations and different styling concepts have resulted in new designs. Steel bumper systems fall into two categories: beams and facebars. Bumper beams are either roll-formed, hot-stamped, or use a combination of both manufacturing processes. For example, the 2011 Ford Mustang bumper beams have roll-formed closed sections that are subsequently hot-stamped and direct water quenched. Unlike bumper beams, facebars are exposed and have an internal supporting structure. They are all stamped except for the 2011 Ford Raptor bumper which is sheet hydroformed. Roll-formed bumpers are the most common type in North America with approximately 72% of the steel bumper market. They are usually manufactured from cold rolled uncoated UHSS with a tensile strength range of 860 to 1500 MPa and a thickness range of 1.1 to 2.0 mm. The most common UHSS grades currently used for roll-formed bumpers are recovery annealed, DP980, and Martensitic Steel. Hot-stamped bumpers make up approximately 10% of the steel bumper market in North America. However, they are expected to gradually gain market share with increased hot-stamping capacity. Hot-stamped bumpers can be manufactured from either aluminized coated or uncoated MnB steel with a minimum tensile strength of 1500 MPa after hot-stamping. Both hot rolled and cold rolled MnB steels are used for hot-stamped bumpers with a thickness range of 1.0 to 4.0 mm. Hot stamped bumpers have the lowest average mass of all steel bumper systems. Facebars are most commonly used on light-, medium- and heavyduty trucks. Facebars account for 18% percent of the steel bumper market and have an internal supporting structure. Facebars are typically stamped from mild- or high-strength low-alloy steels with tensile strengths up to 500 MPa and a thickness range of 1.6 to 2.3 mm. Since facebars are exposed, cold-rolled steel is typically used to improve surface quality and coating appearance. Facebars are polished either prior to or after stamping, or both, and then chromed or painted on the exposed surfaces, depending on customer preference. x

14 Steel is well positioned in the bumper system market with 83% market share. However, the graphs on page xii show that aluminum is starting to gain ground as mass reduction becomes more important to automotive OEMs. Steel bumpers must be further optimized due to the strong focus on weight reduction and improving vehicle fuel economy. This can be accomplished by increasing the strength levels of UHSS. In the near future, stronger UHSS will be available with minimum tensile strengths up to 1900 MPa. Work is also underway evaluating the use of AHSS in bumper facebar applications. Bumper suppliers will also be looking harder at advanced manufacturing technologies to reduce mass. These include, but are not limited to, tailored blanks, tailor welded coils, tailor rolled blanks, tailor rolled coils, 3D roll-forming, and sheet hydroforming. The steel bumper market, at approximately 400,000 tons per year, is important to the North American steel industry. For this reason, the Automotive Applications Council of the Steel Market Development Institute (SMDI) established a Bumper Project Team. SMDI s Bumper Project Team is a group of experts from the steel industry, Tier-1 bumper suppliers, and OEMs. The Team is dedicated to keeping steel the material of choice for bumper applications. They accomplish this by sharing information related to Bumper manufacturing processes, steel grades, and regulations, solving problems associated with steel bumper development, and completing R&D projects that address new design challenges for bumpers and/or make them more cost and mass efficient. The Bumper Project Team prepared this technical information bulletin to provide fundamental background information on North American bumper systems. xi

15 NORTH AMERICAN BUMPER SYSTEM MARKET SHARE BY MATERIAL 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% ALUMINUM % 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% COMPOSITES % 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% STEEL 2012 xii Source: Ducker Worldwide (Reference 1.1)

16 Objective The purpose of this publication is to increase the reader s understanding of passenger car and light truck bumper systems. It is an overview of an automotive component system, which has undergone significant change in recent years. The information provided is aimed at automotive industry design, manufacturing, purchasing and safety related staffs; and steel industry sales and marketing groups. The emphasis is on materials, design, manufacturing, government regulations and cost. This document is intended to give the reader in depth knowledge regarding the bumper industry. While the attempt is made to cover all materials, manufacturing methods and bumper designs, some information may not be present. An emphasis has been placed on presenting the most common practices and materials, however additional information has also been presented to give the reader some ideas for possible future bumper designs, manufacturing methods and materials. It is a living document and revisions and additions will be made as experience is gained. The Bumper Project Group hopes this publication will increase the reader s knowledge of bumper systems and help overcome engineering challenges. xiii

17 1. Bumper systems and components 1.1 Bumper systems System selection Metal facebar system There are several factors that an engineer must consider when selecting a bumper system. The most important factor is the ability of the bumper system to absorb enough energy to meet the OEMs internal bumper standard. Weight, manufacturability and cost are also important factors that engineers consider during the design phase. The formability of materials is important for high-sweep bumper systems. Another factor considered is recyclability of materials, which is a definite advantage for steel. As shown in Figure 1.1, there are five bumper systems in common use today: A. Metal facebar B. Plastic fascia and reinforcing beam C.Plastic fascia, reinforcing beam and mechanical energy absorbers D.Plastic fascia, reinforcing beam and foam or honeycomb energy absorber E. Plastic fascia, reinforcing beam, foam, and mechanical energy absorbers A metal facebar system, as shown in Figure 1.1 A, consists of a single metallic bumper that decorates the or end of a vehicle and acts as the primary energy absorber in a collison. The bumper regulations in the United States require passenger cars to withstand a 2.5 mph (4 km/h) impact at the curb position plus or minus two inches (50mm) with no visual damage and no damage to safety related items. The North American OEMs voluntarily design their passenger car bumpers to withstand a 5 mph (8 km/h) impact with no visual damage and no damage to safety items. Current facebar systems can only withstand a 2.5 mph (4 km/h) impact at the curb position plus or minus 2 inches (50mm) with no visual damage and no damage to safety items. For this reason, the use of current facebar systems is restricted to light trucks, often to meet voluntary internal OEM design standards. The aesthetics of facebars match the styling trend for full size vans, pickups and sport utilities. Thus, most facebars are presently being applied to these vehicles. If the voluntary internal OEM design standard for light truck bumpers were to rise to the 5 mph (8 km/h) voluntary passenger car standard, then the facebar systems used on full size vans, pickups and sport utilities would have to be redesigned. For the reason of weight, such redesigns would likely revert to systems that employ a reinforcing beam. 1-1

18 FIGURE 1.1 COMMON BUMPER SYSTEMS A. B. C. D. E. 1-2

19 1.1.3 Plastic fascia and reinforcing beam system This system, as shown in Figure 1.1 B, consists of a plastic fascia and a reinforcing beam that is fastened directly to the vehicle frame or motor compartment rails. It is primarily used for bumper systems in passenger cars since the crash requirements are less severe and there is less need for mechanical energy absorbers and foam Plastic fascia, reinforcing beam and energy absorption system Bumper systems with a plastic fascia, reinforcing beam and energy absorption systems are the most common type of bumper system in North America. They are used on both and bumper systems and readily meet the 5 mph (8 km/h) voluntary bumper standard set by North American OEMs. While most passenger cars, SUVs, crossovers, and minivans, have this type of bumper system, the energy absorption method varies. The reinforcing beam always absorbs a significant amount of energy while additional energy can be absorbed by mechanical energy absorbers (Fig. 1.1C), foam or honeycomb (Fig. 1.1D), or both (Fig. 1.1E). 1.2 Bumper components Fascia Bumper fascias (Figure 1.1) are designed to meet several requirements. They must be aerodynamic to control the flow of the air around the car and the amount of air entering the engine compartment. They must be aesthetically pleasing to the consumer. Typical fascias are styled with many curves and ridges to give bumpers dimension and to distinguish vehicles from competing models. Another requirement of bumper fascias is that they be easy to manufacture and light in weight. Virtually all fascias are made from one of three materials: polypropylene, polyurethane or polycarbonate Energy absorbers Energy absorbers (Figure 1.1) are designed to absorb a portion of the kinetic energy from a vehicle collision. Energy absorbers are very effective in a low speed impact, where the bumper springs back to its original position. Energy absorber types include foam, honeycomb and mechanical devices. All foam and honeycomb absorbers are made from one of three materials: polypropylene, polyurethane or low-density polyethylene. Mechanical energy absorbers, also referred to as crush cans, are metallic and sometimes resemble shock absorbers. Although mechanical energy absorbers have several times the weight of a foam energy absorber, they are also capable of absorbing several times the energy. Most bumper systems use mechanical energy absorbers due to higher energy absorption requirements. 1-3

20 1.2.3 Facebar Facebars (Figure 1.1) are usually stamped from steel with plastic or stainless steel trim to dress them up. Steel facebars, for formability reasons, are usually made from steels with a low to medium yield strength. Higher strength steels are being investigated for facebars to reduce the thickness and weight. After stamping, steel facebars are chrome plated or painted for appearance and corrosion protection reasons Reinforcing beam The reinforcing beams (Figure 1.1) are key components of the bumper systems that employ them. Reinforcement beams help absorb the kinetic energy from a collision and provide protection to the rest of the vehicle. By staying intact during a collision, beams preserve the frame. Design considerations for reinforcing beams include strength, manufacturability, weight, recyclability and cost. Steel reinforcing beams are usually roll formed or hot stamped using ultra high-strength steel. Typical cross sections are shown in Figure 1.2. Roll formed beams are the most common but hot stamped beams have the lowest average mass of all steel bumper systems and are becoming more popular as a result. The most common cross section for roll formed beams is the B-section and the most common sections for hot stamped beams are box and hat sections. Sometimes a stamped or roll formed face or back plate is welded to a roll formed or hot stamped C-section to create a boxed section. Additional reinforcements are sometimes welded to reinforcing beams, such as pole protectors and bulkheads. All steel reinforcing beams receive corrosion protection. Some beams are made from hot-dip galvanized or electrogalvanized sheet. The zinc coating on these products provides excellent corrosion protection. Other beams are protected after fabrication with a paint system such as. Since steel reinforcing beams are becoming stronger and lighter with thinner gauges being used, more beams are using both zinc coating and ing to meet corrosion protection requirements. 1-4

21 1.3 Types of bumper beams Steel Reinforcing Beams Steel Facebars Plastic Reinforcing Beams Steel reinforcing beams are produced using the cold stamping, hot forming or roll forming processes. The tensile strength of cold stamped and roll formed beams ranges from MPa ( ksi). The tensile strength of hot stamped beams, after heating and quenching, ranges from MPa ( ksi). All steel beams have an elastic modulus of 207,000 MPa (30,000 ksi). Steel reinforcing beams are protected from corrosion by zinc coatings, aluminum coatings or electrocoatings. After mounting to a vehicle frame, reinforcing beams are covered by cosmetic or energy absorbing fascias. Steel facebars are typically cold stamped from low-carbon and high-strength steels having tensile strengths from MPa (50-72 ksi) and an elastic modulus of 207,000 MPa (30,000 ksi). They are either chrome plated or painted for corrosion protection and appearance before being mounted to a vehicle s frame. Most facebars are dressed up with plastic trim. There are two types of plastic beams glass reinforced plastic or unreinforced plastic. Examples of glass reinforced plastic beams include polypropylene (compression molded), unsaturated polyester (compression molded) and polyurethane (reaction injection molded). Examples of unreinforced plastic beams include polycarbonate/polybutylene (injection or blow molded), polyethylene (blow molded) and polypropylene (blow molded). Plastic beams have tensile strengths up to 275 MPa (40 ksi) and flexural moduli up to 15,000 MPa (2,200 ksi) Aluminum Reinforcing Beams Typically, aluminum beams are made by stretch or press forming extruded shapes made from the 6000 and 7000 aluminum series. After forming and heat treating, the beams have tensile strengths up to 550 MPa (80 ksi) and an elastic modulus of 69,000 MPa (10,000 ksi). 1-5

22 FIGURE 1.2 COMMON REINFORCING BEAM OSS SECTIONS Roll Formed Box Section Hat Section Roll Formed C Channel Section Hat Section Welded to Face or Back Plate Roll Formed B Section 1-6

23 2. Steel materials 2.1 Introduction Flat rolled steels are versatile materials. They provide strength and stiffness with favorable mass-to-cost ratios, and they allow high speed fabrication. In addition, they offer excellent corrosion resistance when coated, high energy absorption capacity, good fatigue properties, high working hardening rates, aging capability, excellent paintability, and complete recyclability. These characteristics, plus the availability of high-strength and ultra high-strength steels, have made sheet steel the material of choice in the automotive industry. Numerous steel types and grades offer designers a wide choice for any given application. Bumper steels with elongations up to 50% facilitate forming operations. Bumper steels with tensile strengths over 1900 MPa (280 ksi) facilitate mass reduction. Low-carbon steels have excellent ductility. They are widely used for body and underbody components that are formed by stamping, roll forming or hydroforming. However, in order to reduce component mass, low-carbon steels are gradually being replaced by steels of greater strength. As the name implies, dent resistant steels are commonly used for body panels such as quarter, door and hood. Their relatively low as-received yield strength facilitates forming. Cold work of forming and bake hardening during the automotive paint cycle increase their yield strength and dent resistance. Microalloy steels usually have less ductility than lowcarbon and dent resistant steels. However, they can be supplied with the necessary ductility to produce most automotive parts. Carbon-Boron steel has good formability and high yield strength after heat treating. Dual phase steel also offers good formability. Its strength increases significantly through cold work during the fabrication process. Recovery annealed and martensitic steels have ultra high yield strengths. However, their formability limits their use to roll formed sections and less severe stampings. Stainless steels offer excellent corrosion resistance, excellent formability and high yield strength. 2-1

24 2.2 Typical properties of steel grades for facebars The steel grades that are commonly used for facebars are shown with their typical properties in Table 2.1. Most facebars are made from highstrength steel [minimum yield strength higher than 240 MPa (35 ksi)]. Although dual phase steels are not listed in Table 2.1, successful trials have been completed and facebars are expected to switch over to this grade for mass reduction. For comparative purposes, Table 2.1 also includes similar SAE grades. The Society of Automotive Engineers (SAE) designates SAE steel grades. These are four digit numbers which represent chemical composition standards for steel specifications. It is important to note that the similar SAE grades are not equivalent grades. That is, there are minor differences between the SAE grades and the common grades to which they are similar. The differences might be significant in some applications. Some OEM s specify grades that can be proprietary in nature. Facebars, due to their depth of draw and complex shape, are produced by the stamping process. Steels of high formability are required and all of the grades shown in Table 2.1 can be supplied to meet the demanding requirements of a facebar stamping. Facebars are either powder coated, painted or chrome plated and a high-quality surface is required on the steel sheet. In addition, the majority of the sheet steel used for plated facebars is flat polished prior to the stamping operation. 2.3 Typical properties of steel grades for brackets, supports and reinforcing beams The steel grades that are commonly used for brackets, supports and reinforcing beams, are shown with their typical properties in Table 2.2. Most reinforcing beams are made from ultra high-strength steel [minimum tensile strength greater than 550 MPa (80 ksi)]. For comparative purposes, Table 2.2 also includes similar SAE grades. It is important to note that the similar SAE grades are not equivalent grades. That is, there are minor differences between the SAE grades and the common grades they are similar to. The differences might be significant in some applications. All of the high-strength steel grades in Table 2.2 can be supplied with sufficient formability for the production of stamped brackets, supports and reinforcing beams. They can also be readily roll formed into reinforcing beams. Generally speaking, the ultra high-strength steel grades in Table 2.2 have less formability than the high-strength grades listed. However, they offer significant weight reduction opportunities and are commonly used for less severe stampings and roll formed reinforcing beams. Grades 120XF and 135XF have sufficient ductility to produce stampings, including reinforcing beams, provided the amount of draw is minimal. Grade 140T has a relatively low as-delivered yield strength, which facilitates stamping and roll forming operations. An advantage of this grade is the fact it work-hardens significantly during forming. In fact, the yield strength after forming approaches 965 MPa (140 ksi). Thus, 140T offers sufficient formability to produce roll formed beams with a large sweep and it provides high yield strength in the finished part. Grades 140XF and M130HT through M250HT have low formability and their use is generally restricted to roll formed reinforcing beams since roll forming is a process of gradual bending without drawing. The Carbon-Boron grades can be used to produce complex parts through the hot stamping process. After quenching, the parts have yield strengths up to 1300 MPa (190 ksi) and tensile strengths up to 2000 MPa (290 ksi). The stainless steel grades are readily stamped or roll formed. Their excellent corrosion resistance eliminates the need for protective coatings. 2-2

25 TABLE 2.1 STEEL GRADES FOR POWDER COATED, PAINTED & CHROME PLATED FACEBARS TYPICAL PROPERTIES AS-SHIPPED FROM THE STEEL MILL MATERIAL GRADE (COMMON NAME) DESIPTION TYPICAL YIELD STRENGTH MPa (ksi) TYPICAL TENSILE STRENGTH MPa (ksi) TYPICAL ELONG (%) TYPICAL "n" VALUE SIMILAR SAE GRADE HR HR HR HR HR HR HR 1008/ XLF 50XLF 55XLF 60XLF 70XLF 80XLF Low-carbon Microalloy Microalloy Microalloy Microalloy Microalloy Microalloy 269 (39.0) 331 (48.0) 403 (58.5) 439 (63.7) 475 (68.9) 527 (76.5) 587 (85.1) 386 (56.0) 407 (59.0) 480 (69.6) 505 (73.2) 531 (77.0) 600 (87.0) 673 (97.6) J J2329 Grade 2 J X J X J X J X J X 1008/1010 DR210 35XLF 40XLF 50XLF 55XLF 60XLF 70XLF 80XLF Low-carbon Dent resistant Microalloy Microalloy Microalloy Microalloy Microalloy Microalloy Microalloy 296 (42.9) 220 (31.9) 285 (41.3) 315 (45.7) 376 (54.5) 418 (60.6) 459 (66.5) 530 (76.8) 592 (85.8) 331 (48.0) 360 (52.2) 400 (58.0) 425 (61.6) 475 (68.9) 501 (72.7) 527 (76.5) 614 (89.1) 690 (100.0) J J A J2329 Grade 2 J X J X J X J X J X J X SS SS T301 T204 Austenitic Austenitic 276 (40) 370 (53.8) 758 (110.0) 689 (100.0) J405 S30100 J405 S20400 NOTES: HR Hot rolled sheet Cold rolled sheet 1008/1010 Low-carbon commercial quality (CQ). Mechanical properties are not certified. DR XLF SS Dent resistant quality. Strength increases due to work hardening during forming. Designation number (e.g. 210) is minimum yield strength in MPa. Microalloy quality. Strength is obtained through small quantities of alloying elements such as vanadium and niobium. Designation number (e.g. 50) is minimum yield strength in ksi. Stainless steel 2-3

26 TABLE 2.2 STEEL GRADES FOR BRACKETS, SUPPORTS AND REINFORCING BEAMS TYPICAL PROPERTIES AS-SHIPPED FROM THE STEEL MILL MATERIAL GRADE (COMMON NAME) DESIPTION HIGH-STRENGTH STEEL GRADES HR 50XLF Microalloy HR 55XLF Microalloy HR 60XLF Microalloy HR 70XLF Microalloy HR 80XLF Microalloy TYPICAL YIELD STRENGTH MPa (ksi) ( ) 403 (58.5) 439 (63.7) 475 (68.9) 527 (76.5) 587 (85.1) TYPICAL TYPICAL TYPICAL SIMILAR SAE TENSILE ELONG "n" GRADE STRENGTH (%) VALUE MPa (ksi) ( ) 480 (69.6) J X 505 (73.2) J X 531 (77.0) J X 600 (87.0) J X 673 (97.6) J X 50XLF Microalloy 55XLF Microalloy 60XLF Microalloy 70XLF Microalloy 80XLF Microalloy 376 (54.5) 418 (60.6) 459 (66.5) 530 (76.8) 592 (85.8) 475 (68.9) J X 501 (72.7) J X 527 (76.5) J X 614 (89.1) J X 690 (100.0) J X HDG () 50XLF Microalloy HDG () 55XLF Microalloy HDG () 60XLF Microalloy HDG () 80XLF Microalloy ULTRA HIGH-STRENGTH STEEL GRADES HR 10B21(M) Carbon-Boron 379 (54.9) 415 (60.2) 452 (65.5) 641 (93.0) 320 (46.4) 453 (65.7) J X 492 (71.4) J X 531 (77.0) J X 662 (96.0) J X 480 (69.6) 18 N/A J403 10B21 15B21(M) Carbon-Boron 15B24 Carbon-Boron 330 (47.9) 330 (47.9) 500 (72.5) 27 N/A J403 15B (72.5) 27 N/A J403 15B24 Aluminized () 15B21(M) Carbon-Boron 330 (47.9) 500 (72.5) 27 N/A J403 15B21 120XF Recovery Annealed 135XF Recovery Annealed 140XF Recovery Annealed 869 (126) 969 (141) 1010 (147) 883 (128) 12 N/A J R 985 (143) 7.0 N/A (149) 5.6 N/A -- HDG () 120XF Recovery Annealed 876 (127) 889 (129) 11 N/A J R 140T 590T 780T Dual Phase Dual Phase Dual Phase 634 (92) 371 (54) 518 (75) 1034 (150) 634 (92) 834 (121) N/A N/A N/A J DL M130HT Martensitic M160HT Martensitic M190HT Martensitic M220HT Martensitic 923 (134) 1020 (148) 1214 (176) 1420 (206) 1055 (153) 5.4 N/A J M 1179 (171) 5.1 N/A J M 1420 (206) 5.1 N/A J M 1627 (236) 4.7 N/A J M EG () M130HT Martensitic EG () M160HT Martensitic EG () M190HT Martensitic EG () M220HT Martensitic 923 (134) 1020 (148) 1214 (176) 1420 (206) 1055 (153) 5.4 N/A J M 1179 (171) 5.1 N/A J M 1420 (206) 5.1 N/A J M 1627 (236) 4.7 N/A J M NOTES: SS T301 1/4 Hard Condition SS T204 20% Cold Worked 517 (75) 779 (113) 862 (125) J405 S (173) J405 S20400 HR Hot rolled sheet Cold rolled sheet HDG () Hot-dip galvanized (cold rolled base) sheet EG () Electrogalvanized (cold rolled base) sheet Aluminized () Hot dip aluminized (cold rolled base) sheet SS Stainless steel XLF Microalloy quality. Strength is obtained through small quantities of alloying elements such as vanadium and niobium. Designation number (e.g. 50) is mimimum yield strength in ksi...b..(m) Carbon-Boron quality (Modified). Properties are for the steel as-shipped from the steel mill. Strength is achieved through heating and quenching. After quenching, the yield strength is about 1140 MPa (165ksi)..B.. Carbon-Boron quality. Properties are for the steel as-shipped from the steel mill. Strength is achieved through heating and quenching. After quenching, the yield strength is about 1140 MPa (165ksi) XF Recovery annealed quality. Strength is achieved primarily through cold work during cold rolling at the steel mill. Designation number (e.g. 120) is minimum yield strength in ksi. 140T Dual phase quality. Structure contains martensite in ferrite matrix. Properties are for the steel as-shipped from the steel mill. Designation number (e.g. 140) is the minimum tensile strength in ksi. M...HT Martensitic quality. Strength is determined by carbon content. Designation number (e.g. 130) is the minimum tensile strength in ksi. N/A Not applicable. The Carbon-Boron steels listed are intended for hot forming. The Recovery Annealed and Martensitic steels are primarily used in roll forming operations. However, they may be used for stampings provided the amount of draw is minimal. The n value for dual phase steels is very dependent on the range over which it is calculated. 2-4

27 2.4 FutureSteelVehicle Materials Portfolio for Automotive Applications The Future Steel Vehicle (FSV) materials portfolio (Reference 2.1) summarizes steel grades considered in the design of FSV. All are commercially available now or will be in the near future. The AHSS family of products in the portfolio provides a key role for future automotive applications. The combination of new design technologies along with emerging steel grades and advanced steel processing technologies enable optimal component and vehicle lightweighting. AHSS grade development has been driven by the need to achieve better performance in crash energy management with material gauge reduction and subsequent lower mass. Tables 2.3 and Table 2.4 show the steel grades and their generalized properties available for future steel vehicle design including facebars, brackets, supports, and reinforcing beams. There are currently sufficient worldwide steel products available globally from steel producers to meet demand. Detailed information about AHSS grades is available in the WorldAutoSteel AHSS Applications Guidelines document online at Elongation versus tensile strength AHSS (advanced high-strength steel) Guidelines published by World Auto Steel ( (Reference 2.2) provide a comparison between the various families of steel products in the form of tensile strength versus percent total elongation (Figure 2.1). The latter is a good measure of the formability for each material class. Each bubble in the graph represents the typical properties of all steel products in each category of steels, as produced by most of the major steel makers around the world. The steel grades shown in the bubbles are: IF (interstitial free) products IS (isotropic) products Mild (mild steel) products BH (bake hardenable) products CMn (carbon-manganese and carbon-boron) products HSLA (high-strength low-alloy) products TRIP (transformation induced plasticity) products DP, CP (dual phase, complex phase) products AUST. SS (austenitic stainless steel) MART (martensitic) products Boron (hot stamped steel) L-IP (liquid-induced plasticity) TWIP (twinning-induced plasticity) The above bubbles may be placed into four groups: Conventional HSS (high-strength steel), Stainless Steels, AHSS (advanced highstrength steel), and UHSS (ultra high-strength steel). A fifth group, 3rd Generation AHSS, is expected to emerge in the near future, offering ultra high-strengths with higher elongation. 2-5

28 2.5 Elongation versus tensile strength (continued) It is clear from the graph that most of the traditional steel products obey an inverse relationship between strength and ductility. Bucking this trend are the dual phase and complex phase families of steel products. These products, although available for at least twenty-five years, have just recently attracted the attention they deserve for their excellent combination of higher strength and very good ductility, making them suitable for energy-absorption applications. Carrying this concept a step further are the TRIP (TRansformation Induced Plasticity) steels. Although the principles underlying these steel products were available and understood at least thirty years ago, only now are these steels becoming available for automotive body applications. TRIP steels provide further enhanced potential for energy absorption at thinner gauges, thus making it possible for a vehicle structure to provide improved safety at lower mass. 2.6 Elongation versus after-fabrication yield strength The above data are all based on tensile properties obtained from undeformed materials. In actual service the steel sheets are strained during fabrication, which is known to increase their strength and decrease their ductility. Many of the formed parts are also subsequently painted and baked to cure the paint. Although not all steels respond to the straining and baking process many of them do. Key among them are the so-called Bake Hardening (BH), Dual Phase (DP) and TRIP steels. Figure 2.2 shows the yield strength increase from straining and baking for several steel grades. This has no significant effect on forming of the steel but it can certainly affect its performance in service. The effect is usually beneficial as straining and baking increase the stress levels at which permanent deformation begins. 2-6

29 2-7 TABLE 2.3 FSV MATERIALS PORTFOLIO

30 2-8 TABLE 2.4 FSV MATERIALS PORTFILIO (Continued)

31 FIGURE 2.1 ELONGATION VERSUS TENSILE STRENGTH Tensile Strength (MPa) *See Page 2-11 for MnB 2-9

32 FIGURE 2.2 INEASE IN YIELD STRENGTH THROUGH WORK HARDENING (WH) AND BAKE HARDENING (BH) 2-10

33 2.7 Elongation versus tensile strength for hot-formed steel The implementation of press-hardened applications and the utilization of hardenable steels are promising alternatives for optimized part geometries with complex shapes and no springback issues. Hot stamped or press hardened steels typically use blanks that are heated up, formed in a press and rapidly cooled. Hot Formed (HF) steel is typically boron-based, containing percent boron, and is usually referred to as boron steel. (Reference 2.3) The processes used to produce boron steel bestow a unique combination of properties. Direct hot-forming may be used to deform the blank in the austenitic state (at high temperatures) or indirect hot-forming may be used to heat and finish the piece after most forming is completed at room temperature. In either case, the steel undergoes a series of transitions in elongation and strength (as shown in Figure 2.3 below), finishing with a rapid cooling to achieve the final desired mechanical properties. Figure 2.3: Boron steel property transitions in direct hot forming process. 1: Initial, room temperature state where the steel is blanked. 2: Raised temperature state prior to forming. 3: Final strength-elongation achieved after forming and rapid cooling. In direct hot-forming, the boron-based steel is blanked at room temperature and then heated to high enough temperature for austenization. The steel is then formed while hot and quenched in the forming tool, developing the martensitic microstructure. Some special post-forming work may be required to finish the pieces, which are exceptionally high-strength. For indirect-hot forming, the steel is blanked and pre-formed at room temperature. The part is then heated and forming is completed while the steel is in this low strength, high elongation state. A final quench in the die produces the final properties and shape. Parts made from boron steel benefit from several material advantages, including ultra high-strength and improved (reduced) springback. The part remains in the die through the cooling phase, and so springback is virtually xistent. The use of hot formed boron steel is growing rapidly due to its ultra high-strength and good forming properties. 2-11

34 2.8 Yield strength versus strain rate More recently, consideration was given to the impact of the rate of straining of a particular material or component on its performance. Since steel is a strain rate sensitive material, its yield and tensile strength increases as the loading rate increases. This provides further benefits in its ability to sustain and absorb higher loads and higher input energy, such as in the case of deformation of a bumper or other structural component. Again, this is not a new discovery but it was only through the introduction of the advanced vehicle concepts phase of the ULSAB (UltraLight Steel Auto Body) development that this benefit of steel began to be introduced in structural design of automobile components. Considerable effort was then expended in various laboratories around the world to generate tensile data at straining rates ranging from quasi-static (10-3 s-1) to 103 s-1 for many of the above steel grades. The effect of the higher strain rate on the strength and ductility for TRIP 600 and DP 600 steels is provided in Figures 2.4 and 2.5, respectively. The data for these steels and other products of interest for bumper construction are available from many steel producers and can be made available for use in the design of bumpers and other energy-absorbing components. Use of the tensile properties of steels at higher rates of loading has begun in automotive design and is expected to be universally used as more data for more steel grades become available and as automotive designers become more comfortable with the reliability of this data. 2-12

35 FIGURE 2.4 STRESS VERSUS STRAIN AT DIFFERENT STRAIN RATES FOR TRIP 600. THE DATA AT 1000 s -1 WERE OBTAINED USING THE SPLIT HOPKINSON BAR (SHB) METHOD FIGURE 2.5 STRESS VERSUS STRAIN AT DIFFERENT STRAIN RATES FOR DP 600. THE DATA AT 1000 s -1 WERE OBTAINED USING THE SPLIT HOPKINSON BAR (SHB) METHOD 2-13

36 2.9 Sheet steel descriptors Sheet steel is a complex product and there are many methods used to describe it. The following descriptors are often associated with automotive sheet steel: a) Type Chemical composition, microstructure processing method or end use are all used to describe the type of steel. Examples include low-carbon, dent resistant, microalloy, high-strength low alloy, recovery annealed, dual phase, bainitic and martensitic sheet. b) Grade Physical properties such as yield strength, tensile strength or elongation are used to denote a grade. Examples include 180 MPa minimum yield strength and 1500 MPa minimum tensile strength. c) Steel Product The final process that steel receives before shipment from a steel mill is often used to describe a steel product. Examples include hot rolled, cold rolled and coated sheet. d) Metallic Coating The process used to apply a metallic coating or the type of metal in the metallic coating are used to describe steel. Examples include hot-dip galvanized, electrogalvanized and zinc coated sheet. e) Surface Condition Surface smoothness is used to describe sheet steel. Examples are exposed, semi-exposed or unexposed body sheet. In practice, when specifying sheet steel, most (if not all) of the above descriptors are required to fully describe the desired steel product. Published documents, such as those of the Society of Automotive Engineers (SAE) greatly facilitate the correct specification of sheet steel. In this context, the relevant SAE documents are: Categorization and Properties of Low-Carbon Automotive Sheet Steels, SAE J2329 (Reference 2.5) Categorization and Properties of Dent Resistant, high-strength and Ultra high-strength Automotive Sheet Steel, SAE J2340 (Reference 6.4) Selection of Galvanized (Hot Dipped and Electrodeposited) Steel Sheet, SAE J1562 (Reference 2.6) Chemical Compositions of SAE Carbon Steels, SAE J403 (Reference 2.7) Chemical Compositions of SAE Wrought Stainless Steels, SAE J405 (Reference 2.8) 2-14

37 2.10 SAE J2329 Low-carbon sheet steel This SAE Recommended Practice furnishes a categorization procedure to aid in selecting low-carbon sheet steel. The system employs four characters. The first two alphabetic characters denote hot rolled (HR) or cold rolled () method of manufacture. The third character defines grade (one through five) based on yield strength range, minimum tensile strength, minimum percent elongation, minimum rm value, and minimum n-value. The fourth alphabetic character (E,U,R,F,N or M) classifies the steel type with regards to surface quality and/or aging character. An optional fifth character may be used to restrict carbon content to a minimum of 0.015%. If the sheet steel is a metallic coated product, then the ing would be specified in accordance with SAE J1562 (see Section 2.10). Examples of typical specification and ordering descriptions for automotive sheet steel are given in Section Steel grade There are five grades of cold rolled sheet and three grades of hot rolled sheet. Mechanical properties are shown in Tables 2.5 and 2.6, while chemical composition is shown in Table 2.7 (page 2-26) Types of cold rolled sheet There are two types of cold rolled sheet, either in the bare or coated condition: E U Exposed. Intended for critical exposed applications where painted surface appearance is of primary importance. Unexposed. Intended for unexposed applications Types of hot rolled sheet There are four types of hot rolled sheet, either bare or in the metallic coated condition: R F N M A coiled product straight off the hot mill, typically known as hot roll black band. A processed product in coils or cut lengths. The product may be susceptible to aging and coil breaks. A processed product in coils or cut lengths. The product is non-aging at room temperature but is susceptible to coil breaks. A processed product in coils or cut lengths. This product is non-aging at room temperature and free from coil breaks. When specifying a hot rolled sheet, the surface condition should also be indicated (E or U as per Section 2.8.2). 2-15

38 2.11 SAE J2340 Dent resistant, high-strength and ultra high-strength sheet steel Steel grade This SAE Recommended Practice defines mechanical properties for dent resistant, high-strength and ultra high-strength sheet steel. The properties for dent resistant steels are shown in Table 2.8, the properties for high-strength steels in Tables 2.9 and 2.10, and the properties for ultra high-strength steels in Table 2.11 (page 2-28). It should be noted that the yield and tensile strength values for the ultra high-strength steels covered by J2340 (Table 2.11) are those commonly used in Europe. For example, J2340 and Europe use values such as 600, 800, 1000 and On the other hand, values such as 590, 780, 980 and 1180 are widely used in North America and Japan. Currently, SAE s Iron and Steel Technical Committee is revising J2340 to cover ultra high-strength steel grades widely used not only in Europe but also in North America and Japan. SAE J2340 also furnishes a categorization procedure to aid in selecting dent resistant, high-strength and ultra high-strength steels. The system employs several characters: The first two characters denote hot rolled (HR) or cold rolled () method of manufacture. The next three or four characters denote the grade of steel. Minimum yield strength in MPa is used for dent resistant and high-strength steels and minimum tensile strength in MPa is used for ultra high-strength steels. Refer to Tables The final set of characters denotes the steel type. Refer to Section If the sheet steel is a metallic coated product, then the ing would be specified in accordance with SAE J1562 (see Section 2.10). Examples of typical specification and ordering descriptions for automotive sheet are given in Section In Tables 2.8, 2.9 and 2.10 (dent resistant and high-strength steels) grade is the minimum yield strength in MPa. In Table 2.11, (ultra high-strength steels) grade is the minimum tensile strength in MPa. 2-16

39 Steel type In Tables 2.6 to 2.9, type is defined by one or two letters as follows: A B AT, BT S X Y SF,XF,YF R DL DH M A non-bake hardenable dent resistant steel in which increase in yield strength due to work hardening results from strain during forming. A bake hardenable dent resistant steel in which increase in yield strength due to work hardening results from strain during forming and an additional increase in yield strength that occurs during the paint-baking process. These types are similar to Types A and B respectively, except that the steel is interstitial free. A high-strength steel, which is solution strengthened using C and Mn in combination with P or Si. A high-strength steel typically referred to as HSLA. It is alloyed with carbide and nitride forming elements (commonly Nb (Cb), Ti and V) in combination with C, Mn, P and Si. A high-strength steel similar to Type X, except the spread between the minimum yield and tensile strengths is larger (100 MPa versus 70 MPa). These types are similar to types S, X and Y respectively, except they are sulphide inclusion controlled. A high-strength steel that has been recovery annealed or stress-relief annealed. Its strength is primarily achieved through cold work during cold rolling at the steel mill. A dual phase ultra high-strength steel. Its microstructure is comprised of ferrite and martensite. The strength level is dictated by the volume of low-carbon martensite. DL dual phase has a low ratio of yield-to-tensile strength (less than or equal to 0.7). A dual phase ultra high-strength steel similar to Type DL, except it has a high ratio of yield to tensile strength (greater than 0.7). A martensitic ultra high-strength steel whose carbon content determines the strength level Hot rolled, cold reduced and metallic coated sheet The steels in Tables 2.8 to 2.11 can be specified as either hot rolled sheet or cold rolled sheet in either the bare or metallic coated condition. Hot-dipped or electrogalvanized coated sheets are covered by SAE J1562 (Section 2.12). All of the steels shown in Tables 2.8 to 2.11 may not be commercially available in all types of coatings. Consult your steel supplier. Also, hot rolled sheet for the steels shown in Tables 2.8 to 2.11 may not be commercially available in thicknesses below mm. Again, consult your steel supplier. 2-17

40 Surface conditions for cold reduced and metallic coated sheet Cold reduced and metallic coated sheet steel is available in three surface conditions: E U Z Exposed. Intended for critical exposed applications where painted surface appearance is of primary importance. Unexposed. Intended for unexposed applications. Semi-exposed. Intended for non-critical exposed applications Conditions for hot rolled sheet Four conditions of hot rolled sheet are available: P W N V A coiled product straight off the hot mill, typically known as hot roll black band. A processed product in coils or cut lengths. The product may be susceptible to aging. A processed product in coils or cut lengths. The mechanical properties do not deteriorate at room temperature. A processed product in coils or cut lengths. The mechanical properties do not deteriorate at room temperature. The product is free of coil breaks. When specifying a hot rolled sheet, the desired surface condition should also be indicated (E,U or Z as per Section ) SAE J1562 Zinc and zinc-alloy coated sheet steel Galvanizing processes This SAE Recommended Practice defines preferred product characteristics for galvanized coatings applied to sheet steel. A galvanized coating is defined as a zinc or zinc-alloy metallic coating. Two generic processes for metallic coated sheets are currently used in the automotive industry: Hot-dip process. A coil of sheet steel is passed continuously through a molten metal bath. Upon emergence from the bath, the molten metal coating mass is controlled by air (or other gas) knives or mechanical wipers before the coating solidifies. This process produces a sheet with a coating on two sides. Electrodeposition process. This continuous coating process uses cells in which the metallic coating is electrodeposited on a coil of sheet steel. This process can produce a sheet with a coating on either one or two sides. 2-18

41 Types of coatings Coating mass The types of commercially produced metallic coatings include: Hot-dip galvanized. Essentially a pure zinc coating applied by the hot-dip galvanizing process. Electrogalvanized. Essentially a pure zinc coating applied by the electrodeposition galvanizing process. Galvannealed. A zinc-iron alloy coating applied by the hot-dip galvanizing process. The coating typically contains 8-12% iron by weight. Alloy. Aluminum-zinc silicon alloy (55%, 43% and 2% by weight respectively) and zinc-aluminum alloy (5% aluminum by weight) coatings are applied by the hot-dip galvanizing process. Zinc-iron alloy (<20% iron by weight) and zinc-nickel (<20% nickel by weight) coatings are applied by the electrodeposition process. Zinc coated sheet (hot-dip galvanized and electrogalvanized) offers superior corrosion resistance. Through sacrificial electrochemical action, zinc coatings protect bare (cut) edges. Galvanneal, due to its lighter zinc content, has less corrosion resistance than pure zinc coatings. However, its iron content provides enhanced spot weldability and paintability. Hot-dip galvanized, electrogalvanized and galvanneal are, by far, the most commonly used coatings for vehicle components. Zinc-aluminum and zinc-nickel coatings have niche applications. For example, zinc-aluminum alloy offers improved corrosion resistance to acids; hence, it is often used for mufflers. Coating mass is expressed in g/m2. The approximate thickness of a coating in microns = g/m2 x The approximate thickness of a coating in mils = g/m2 x The heavier the coating mass, the greater the corrosion resistance of a metallic coated sheet. However, spot weldability decreases with an increase in coating mass Surface quality Three surface qualities may be specified: Exposed Semi-exposed Unexposed Coated sheet thickness The thickness of metallic coated sheet steel is determined by measuring, as a single unit, the combination of the base sheet steel and all metallic coatings. 2-19

42 Coating designations SAE J2329 uses a nine-character designation system to identify the galvanizing process, the ing type and mass of each side of the sheet and surface quality. The first and second characters denote the galvanizing process: HD = hot-dip galvanized EG = electrogalvanized (electrodeposition) The third and fourth characters denote the coating mass of the unexposed side in accordance with Table 2.12 (page 2-30). The fifth character denotes the ing type of the unexposed side: G = pure zinc A = zinc-iron N = zinc-nickel X = other than G, A or N The sixth and seventh characters denote the ing mass of the exposed side in accordance with Table 2.12 The eighth character denotes the ing type of the exposed side: G = pure zinc A = zinc-iron N = zinc-nickel X = other than G, A or N The ninth character denotes surface quality: E = Exposed Z = Semi-exposed U = Unexposed 2.13 SAE J403 Carbon steel chemical compositions Examples of typical specification and ordering descriptions for automotive sheet steel are given in Section This SAE Recommended Practice provides chemical composition ranges for carbon steels supplied to certified chemical composition rather than to certified mechanical properties. SAE J403 uses a four or five character system to designate steel grade: The first two characters are the number 10, which indicate that the grade is carbon steel. The last two characters represent the nominal carbon content of the grade in points of carbon. One point of carbon is 0.01% carbon by weight. Five points would be shown as 05, fifteen points as 15, etc. If boron is added to a carbon steel to improve hardenability, the letter B is inserted between the first two characters and the last two characters. Examples of typical specification and ordering descriptions for automotive sheet are given in Section

43 Carbon sheet steel SAE J403 provides compositions for carbon grade sheet steels. Table 2.13 (page 2-30) shows the compositions for grades 1006 through SAE J403 provides compositions for grades 1006 through However, grades above 1025 have relatively low formability and weldability due to their relatively high carbon content. Thus, grades above 1025 are seldom used for automotive sheet applications. It is important to note that sheet steels specified or ordered to SAE J403 are not supplied with certified mechanical properties. If certified mechanical properties are required, automotive sheet steel should be specified or ordered in accordance with SAE J2329 (Section 2.10) or SAE J2340 (Section 2.11) Boron sheet steel The addition of boron to carbon sheet steel improves its hardenability. For this reason, boron sheet steel is an ideal material for hot stampings. As an example, 10B21 (Modified) is used for hot stamped bumper reinforcing beams. As received, this steel has a yield strength in the range MPa. Following hot stamping and quenching in liquid-cooled dies, the yield strength is raised to about 1140 MPa. Currently, SAE s Iron and Steel Technical Committee is revising J403 to more appropriately cover sheet steel used for hot stampings SAE J405 Wrought stainless steels This SAE Standard provides chemical composition requirements for wrought stainless steels supplied to chemical composition rather than to certified mechanical properties. The standard uses three series to designate stainless steel grades: S20000, S30000 and S S20000 designates nickel-chromium-manganese, corrosion resistant types that are nonhardenable by thermal treatment. S30000 designates nickel-chromium, corrosion resistant steels, nonhardenable by thermal treatment. S40000 includes both a hardenable, martensitic-chromium steel and nonhardenable, ferritic-chromium steel. Table 2.14 (page 2-30) shows the chemical compositions for two stainless steel grades that are appropriate not only for bumper facebars but also for bumper reinforcing beams. 2-21

44 2.15 SAE Specification and ordering descriptions The following examples represent typical specification and ordering descriptions for automotive sheet steel: a) SAE J2329 2E Cold rolled sheet steel, grade 2 (Tables 2.5 & 2.7), exposed surface condition. b) SAE J2329 HR3MU Hot rolled sheet steel, grade 3 (Tables 2.6 & 2.7), non-aging at room temperature and free from coil breaks, unexposed surface condition. c) SAE J2329 4C EG60G60GE Cold rolled sheet steel, grade 4 (Tables 2.5 & 2.7), minimum carbon 0.015%, each side electrogalvanized coated to 60g/m 2, critical exposed surface condition. d) SAE J2329 HR2M 45A45AU Hot rolled sheet steel, grade 2 (Tables 2.6 & 2.7), non-aging at room temperature and free from coil breaks, each side galvannealed coated to 45g/m 2, unexposed surface condition. e) SAE J A Cold reduced sheet steel, grade HD70G70GZ 180 non-bake hardenable dent resistant (Table 2.8), each side hot-dip galvanized coated to 70g/m 2, semi-exposed surface condition. f) SAE J B Cold reduced sheet steel, grade EG70G70GE 250 bake hardenable dent resistant (Table 2.8), each side electrogalvanized coated to 70g/m 2, critical exposed surface condition. g) SAE J2340 HR 340XU Hot rolled sheet steel, grade 340 high-strength low-alloy (Table 2.9), unexposed surface condition. h) SAE J MU Cold reduced sheet steel, grade 1300 ultra high-strength martensitic (Table 2.11), unexposed surface condition. i) SAE J1562 EG70G70GE Electrogalvanized sheet having a 70 g/m 2 minimum zinc coating (Table 2.12) on each side for an exposed application. 2-22

45 j) SAE J1562 HD70G20AE Hot-dip galvanized sheet having a 70g/m 2 minimum zinc coating (Table 2.12) on the unexposed side and a 20g/m 2 minimum zinc-iron coating (Table 2.12) on the exposed side for an exposed application. k) SAE J1562 HD90G90GU Hot-dip galvanized sheet having a 90g/m 2 minimum coating (Table 2.12) on each side for an unexposed application. l) SAE J1562 HD45A45AU Hot-dip galvanized sheet having a 45g/m 2 minimum zinc-iron coating (Table 2.12) on each side for an unexposed application. m) SAE J1562 EG30N30NE Electrogalvanized sheet having a 30g/m 2 minimum zinc-nickel coating (Table 2.12) on each side for an exposed application. n) SAE J1562 EG70G00XE Electrogalvanized sheet having a 70g/m 2 minimum zinc coating (Table 2.12) on the unexposed side and no coating on the exposed side for an exposed application. o) SAE J403 HR1010U Hot rolled sheet steel, grade 1010 (Table 2.13), unexposed surface condition. p) SAE J403 Hot rolled sheet steel, grade HR1008HD90G90GU 1008 (Table 2.13), having a 90g/m 2 minimum coating on each side for an unexposed application. 2-23

46 2.16 ASTM A463 Aluminized sheet steel Aluminized sheet steel is intended principally for heat resisting applications and for uses where corrosion resistance and heat are involved. One application is hot formed bumper beams. Aluminized sheet has an aluminum-silicon alloy on each side applied by a continuous hot-dip process. The coated sheet has the surface characteristics of aluminum with the superior strength and lower cost of steel. One specification, which describes aluminized steel, is ASTM A463 (Reference 2.8). The quality of the sheet steel can be commercial (CS Types A, B and C), forming (FS), deep drawing (DDS), extra deep drawing (EDDS), structural (SS), high-strength low-alloy (HSLAS), high-strength low-alloy with improved formability (HSLAS-F) and ferritic stainless steel (FSS Types 409 and 439). Chemical and mechanical properties are given for all qualities. A463 also defines the type of aluminum-zinc coating and coating weights. For hot formed bumper beams (see Section 3.4), boron steel with a Type 1 coating is commonly used. The mechanical properties of the boron steel are discussed in Section The Type 1 aluminum coating contains about 10% silicon. The coating weight (total both sides) is typically g/m 2 ( oz/ft 2 ). 2-24

47 TABLE 2.5 SAE J2329 LOW-CARBON COLD ROLLED SHEET MECHANICAL PROPERTIES GRADE YIELD MINIMUM MINIMUM MINIMUM MINIMUM STRENGTH TENSILE ELONGATION r m VALUE n-value (MPa) STRENGTH (%) (MPa) 1 N/R N/R N/R N/R N/R N/R N/R = Not Required TABLE 2.6 SAE J2329 LOW-CARBON HOT ROLLED SHEET MECHANICAL PROPERTIES GRADE YIELD MINIMUM MINIMUM MINIMUM STRENGTH TENSILE ELONGATION n-value (MPa) STRENGTH (%) (MPa) 1 N/R N/R N/R N/R N/R = Not Required 2-25

48 TABLE 2.7 SAE J2329 LOW-CARBON HOT & COLD ROLLED SHEET CHEMICAL COMPOSITION GRADE MAXIMUM MAXIMUM MAXIMUM MAXIMUM MINIMUM CARBON MANGANESE PHOSPHORUS SULPHUR ALUMINUM (%) (%) (%) (%) (%) TABLE 2.8 SAE J2340 DENT RESISTANT SHEET STEEL GRADE & AS RECEIVED AS RECEIVED AS RECEIVED YIELD YIELD TYPE YIELD TENSILE n-value STRENGTH STRENGTH STRENGTH STRENGTH AFTER AFTER (MPa) (MPa) 2% STRAIN STRAIN & BAKE (MPa) (MPa) 180A B A B A B A B Type A = Non-bake Hardenable Type B = Bake Hardenable 2-26

49 TABLE 2.9 SAE J2340 HIGH-STRENGTH SOLUTION STRENGTHENED AND LOW-ALLOY SHEET STEEL GRADE & TYPE MINIMUM YIELD STRENGTH (MPa) MAXIMUM YIELD STRENGTH (MPa) MINIMUM TENSILE STRENGTH (MPa) COLD REDUCED MINIMUM ELONGATION (%) HOT ROLLED MINIMUM ELONGATION (%) 300S X Y S X Y X Y X Y X Y X Y Type S = Solution strengthened using C and Mn in combination with P or Si. Type X = HSLA. Alloyed with carbide and nitride forming elements (commonly Nb, Ti and V) in combination with C, Mn, P and Si. Type Y = Similar to Type X, except the spread between minimum yield and tensile strengths is larger (100 MPa versus 70 MPa). TABLE 2.10 SAE J2340 HIGH-STRENGTH RECOVERY ANNEALED SHEET STEEL GRADE & TYPE MINIMUM YIELD STRENGTH (MPa) MAXIMUM YIELD STRENGTH (MPa) MINIMUM TENSILE STRENGTH (MPa) MINIMUM ELONGATION (%) 490R 550R 700R 830R Type R = Recovery annealed or stress-relief annealed

50 TABLE 2.11 SAE J2340 ULTRA HIGH-STRENGTH DUAL PHASE & MARTENSITE SHEET STEEL GRADE & TYPE MINIMUM YIELD STRENGTH (MPa) MINIMUM TENSILE STRENGTH (MPa) MINIMUM ELONGATION (%) 500 DL DH DL DL DH DL DL DL M M M M M M M M Type DL = Dual phase with a yield-to-tensile ratio less than or equal to 0.7. Type DH = Dual phase with a yield-to-tensile ratio greater than 0.7. Type M = Martensitic. 2-28

51 TABLE 2.12 SAE J1562 COATING MASS FOR GALVANIZED SHEET STEEL CATEGORY (DESIGNATION) MINIMUM MASS PER SIDE 1 FOR HOT-DIP OR ELECTROGALVANIZED (g/m 2 ) MAXIMUM MASS PER SIDE 1 FOR HOT-DIP (g/m 2 ) MAXIMUM MASS PER SIDE 1 FOR ELECTROGALVANIZED (g/m 2 ) NA Single spot test. Approximate thickness in microns equals coating mass in g/m 2 multiplied by Approximate thickness in mils = coating mass in g/m 2 multiplied by Not applicable. 2-29

52 TABLE 2.13 SAE J403 CARBON STEEL COMPOSITIONS FOR SHEET GRADE CARBON (%) MANGANESE (%) PHOSPHOROUS (Max %) SULFUR (Max %) Max 0.45 Max Max 0.50 Max Max 0.60 Max Max = Maximum TABLE 2.14 SAE J405 CHEMICAL COMPOSITIONS OF WROUGHT STAINLESS STEELS, % (maximum unless a range is indicated) DESIGNATION C Mn P S Si Cr Ni N S S

53 3. Manufacturing processes 3.1 Stamping The art of science of sheet metal stamping processes are challenged daily to accommodate higher strength and thinner materials. Further, these materials must be transformed into more complex shapes with fewer dies and increased quality in the final part. And, of course, all must be accomplished while reducing costs. Such pressures require a rigorous approach to assessing the current state of a stamping process. A detailed discussion on stamping operations is given in Reference 4.2. However, an overview is outlined below Stretching The concept of major and minor strain can be used to describe different kinds of sheet forming processes. In cases where the sheet is stretched over a punch, the major strain is always positive. For stretching, the minor strain is usually positive as well. Different punch and clamping configurations can create a variety of major and minor strain levels. For stretching, a pulling load in the major strain direction is paired with a zero or positive load applied in the minor strain direction. The minor strain can vary from slightly negative (no applied load in the minor strain direction, as in stretching a strip by pulling on its ends) to positive strain equal to the level of the major strain. A minor strain of zero is a special case, which is often called plane strain. In plane strain, all deformation takes place in only two dimensions; the major strain direction and the thickness direction. All stretching is accommodated by thinning of the material. In circle grid analysis (CGA), small circles are etched on the surface of the steel sheet prior to stamping (Figure 3.1). After stamping, the deformed circles are compared to the original circles (Figure 3.2). For the condition of plane strain, the deformed circle is an ellipse with the minor strain diameter equal to the original diameter of the underformed circle. A minor strain equal to the major strain is indicated by an original circle, which remains circular after deformation. However, the diameter of the circle after deformation is larger than the diameter before deformation. This condition is called equi-biaxial stretch because the amount of the stretch is equal regardless of the direction in the plane of the sheet. 3-1

54 FIGURE 3.1 TYPICAL CIRCLE GRID PATTERN FIGURE 3.2 REPRESENTATION OF STRAINS BY ETCHED CIRCLES 3-2

55 3.1.2 Drawing When a sheet is pulled into a die cavity, and must contract to flow into the cavity in areas such as at a corner or in the flange of a circular cup, the sheet is said to be undergoing drawing. Drawing, also known as deep drawing, generates compressive forces in the flange area being drawn into the die cavity. Negative minor strains are generated. In contrast to failures in stretching, failures in drawing do not normally occur in the flange area where the compression and flow of sheet metal is occurring. Instead, necking and fracture occur in the wall of the stamping near the nose of the punch. Failure occurs here because the force causing the deformation in the flange must be transmitted from the punch through this region. If the force required to deform the flange is too great, it cannot be transmitted by the wall without overloading the wall Bending Bending differs from drawing and stretching, because the deformation present in bending is not homogeneous through the thickness of the material. For pure bending, where there is no superimposed tension or compression on the bending process, the center of the sheet has zero strain. The outer surface is elongated, with a tensile strain equal to t/2r (t=steel thickness, r=bend radius to the midpoint of the steel thickness). The inner surface is compressed, with a compressive strain equal to t/2r. The strain varies from compressive at the inner radius, through zero at the midpoint of the thickness, to tensile at the outside radius. In pure bending, the compressive and tensile strains are equal. Because the strain varies through the thickness, forming limit analysis (Section 3.1.5) does not directly apply. Materials with very little capacity to be formed can frequently undergo bending operations successfully. The tendency to thin locally, with necking and fracture, is not present in bending. Cold working of the material does take place. However, the amount of work hardening depends on the radius of the bend and the thickness of the material. A sharper radius (smaller r) or thicker material (greater t) causes an increase in strain at the surface. Bending is a plane strain operation. The length of the bend does not change during bending, except for localized distortion at the edge of the sheet Bending and straightening As material passes through a draw bead or over a die lip, it is bent, straightened, and sometimes re-bent in the opposite direction. The net strain at the end of this process is small, although cold work has occurred and the material is harder than it was before the process began. As a result, the ability to deform the material in subsequent operations is decreased. 3-3

56 3.1.5 Forming limits The measurement of strain provides an important tool for determining the local deformation that occurs in a complicated process. Sharply changing levels of strain usually indicate a localization of deformation and a higher likelihood of necking and failure during forming. For sheet metal, it has been found that a limit to the major strain exists for each level of minor strain. This phenomenon has been studied in the laboratory and has resulted in the creation of forming limit diagrams. First, flat sheets of a given material are etched with circles as shown in Figure 3.1. The flat sheets are then deformed in a variety of configurations to develop a large range of major and minor strains. If the forming process for any given configuration is continued until failure (as defined by localized necking), the major and minor strains at failure, as shown in Figure 3.2, can be measured for that configuration. By plotting the failure strains of the various configurations, a boundary line indicating the major strain limit for each minor strain is obtained (Figure 3.3). While this limit is not absolute, there is a very high probability of failure above this boundary line and a low probability of failure below this line. The boundary line is frequently called the forming limit curve, and the entire graph, the forming line diagram (FLD). A second forming limit curve, plotted with major strains 10% below those of the boundary line, is sometimes used to provide a safety factor. Each combination of material properties and thickness results in a different FLD. 3.2 Roll forming Cold roll forming is a process whereby a sheet or strip of metal is formed into a uniform cross section by feeding the stock longitudinally through a roll forming mill. The mill consists of a train with pairs of driven roller dies, which progressively form the flat strip until the finished shape is produced. The number of pairs of rolls depends on the type of material being formed, the complexity of the shape being produced, and the design of the particular mill being used. A conventional roll forming mill may have as many as 30 pairs of roller dies mounted on individually driven horizontal shafts. Roll forming is one of the few sheet metal forming processes that is confined to a single primary mode of deformation. Unlike most forming operations that have various combinations of stretching, drawing, bending, bending and straightening, and other forming modes, the roll forming process is nothing more than a carefully designed series of bends. In roll forming, metal thickness is not changed except for a slight thinning at the bend radii. 3-4

57 3-5 FIGURE 3.3 TYPICAL FORMING LIMIT DIAGRAM

58 The roll forming process is particularly suited to the production of long lengths of complex shapes held to close tolerances. Large quantities of these parts can be formed with a minimum of handling and manpower. The process can be continuous by coil feeding and exit cutting to length. Operations such as notching, slotting, punching, embossing and curving can easily be combined with contour roll forming to produce finished parts off the exit end of the roll forming mill. In fact, ultra high-strength steel reinforcing beams, with sweeps up to 50, only need to have the mounting brackets welded to them before shipment to the assembly line. 3.3 Hydroforming There are two types of hydroforming - sheet and tubular. Sheet hydroforming is typically a process where only a female die is constructed and a bladder membrane performs as the punch. High pressure fluid (usually water) forces the bladder against the steel sheet until it takes the shape of the female die. Sheet hydroforming has several advantages versus stamping such as lower tooling costs and less friction during forming. However, it is limited to lower volume applications due to its higher cycle time. In tubular hydroforming, a straight or pre-bent tube is laid into a lower die. The upper and lower dies are then clamped together. Next, conical nozzles are inserted and clamped into each end of the tube. Finally, a fluid (usually water) is forced at a high pressure into the tube until it takes the shape of the die. While tube hydroforming technology has been around for decades, the mass production of automotive parts only became cost effective in about The benefits of hydroforming are usually found via part consolidation and the elimination of engineered scrap. Box sections, consisting of two hat sections welded together, lend themselves to cost-effective replacement by a single hydroformed part. Punches, mounted in the forming dies, are used to pierce holes during forming, eliminating subsequent machine operations. The structural integrity of a hydroformed part, made from a single continuous tube, is superior to that of a part made from two or more components. Weight savings of 10 to 20% can be achieved via both reducing gauge and eliminating weld flanges. If flanges are necessary for attachment, they can be created by pinching the tube during the hydroforming process. High volume tubular hydroformed parts are currently incorporated into automotive components such as subframes, ladder frames, IP beams, roof rails, and exhaust components. 3-6

59 3.4 Hot forming Generally speaking, as the strength of steel increases, its ductility decreases. One method used to overcome the reduced formability of ultra high-strength steel is hot forming. Hot formed bumper beams have very high-strength. They offer not only mass reduction but also large and compound sweeps. Highly complex beams can be produced in one piece. The repeatability of dimensions is very good and there is no springback, a phenomenon which is common with cold forming processes. The hot forming process involves the following steps: Blanking Heating Forming/Quenching De-scaling (if required) The typical material used for hot stamping is boron steel having 0.22% carbon, 0.002% boron, an as-delivered yield strength of 330 MPa (47.9 ksi), an as-delivered tensile strength of 500 MPa (72.5 ksi) and a 15-20% elongation. The boron steel may be bare or aluminized. If aluminized, a hot dip Type 1 coating (10% silicon) and a coating mass of g/m2 ( mils) are common. After heating and quenching, a hot formed part has very high hardness (470 HV). Thus, it is best to punch any required holes into the blank. The developed blanks or pre-formed parts are continuously fed into a furnace. They are heated to austenitizing temperatures, approximately 900ºC (1650ºF). If bare steel is used, the furnace usually has a non-oxidizing atmosphere to suppress scale formation. However, on transfer to the forming/quenching press, some scale will form. If aluminized steel is used, a Fe-Al alloy forms in the furnace on the surface of the steel sheet and scaling is avoided. In the forming/quenching press, the blank/pre-formed section is formed to its final shape using dies maintained at room temperature. The part is held in the die until it is sufficiently quenched. Some tempering is usually required. Tempering may be accomplished by ejecting the part from the forming/quenching dies while it is still fairly hot or by baking the quenched part in an oven. The yield strength of the final hot formed part for a common 10B21 boron steel has increased to about 1140 MPa (165 ksi) and the tensile strength to about 1520 MPa (220 ksi). Elongation has decreased to less than 6%. A part made from aluminized sheet has a hard Fe-Al-Si coating system and is scale free, eliminating the need for de-scaling. Further, this coating system provides corrosion protection for the finished part. A part made from bare sheet does have scale and de-scaling is often employed. 3-7

60 3.5 Bumper beam coatings Steel bumper beams are coated for one or more of the following reasons: To improve appearance To slow or prevent corrosion To increase resistance to wear The side of a facebar is an exposed automotive part and appearance is critical. However, in addition to appearance, the coatings applied to facebars made from hot or cold rolled sheet must also provide adequate corrosion protection and resistance to rock chipping. Zinc coated sheet is not commonly used for facebars. One exception, though, is when the thickness of a facebar is less than 1.00 mm (0.039 inches). In such cases, the zinc provides the extra corrosion protection and rock-chip resistance needed to meet design requirements. Successful trials have been conducted on facebars made from stainless steel. An inherent advantage of such facebars is their corrosion resistance. Thus, stainless steel facebars need only be coated to meet appearance and rock-chip requirements Zinc or zinc-iron coatings Aluminum coating A reinforcing beam is an unexposed part and the main reason for coating it is to improve corrosion resistance. Sometimes, however, reinforcing beams are given a coating to provide not only corrosion resistance but also appropriate underbody appearance. Steel reinforcing beams are made from hot rolled, cold rolled or zinc coated sheet. Bumper beam coatings may be applied by a steel mill, an automotive supplier or an OEM. Steel mills supply sheet with metallic coatings (e.g., zinc, zinc-iron) that have been applied by hot dipping or electrocoating. Automotive suppliers apply metallic (e.g., chromium), organic (e.g.,, paint), autodeposition and powder coatings. The OEMs often apply on their assembly lines. The coatings applied to current bumper beams are shown in Tables 5.4, 5.5 and 5.6. It may be seen that facebars are typically coated with chromium or paint, while reinforcing beams typically receive. These coatings are described in Section This coating is described in Section

61 3.5.3 Polishing In order to achieve a high quality surface after painting or chromium coating, the steel blanks used to stamp facebars must be smooth and free of surface defects. Traditionally, hot rolled sheet has been used for facebars and the following steps taken for the blanks: Ordering to special surface and flatness requirements Pickling Polishing Phosphating and lubricating Chromium coating Chromium coatings are applied using the electroplating process, which places a thin layer of metal on an object through the use of electricity. Although there are variations, the following steps are typically used to place a chromium coating on a fabricated facebar: Polishing manually or automatically to remove die marks, orange peel and shock lines introduced during the stamping process. Cleaning to remove lubricants, polishing compounds and shop soils. Pickling to remove oxides, rust, scale and weld smoke. Rinse. Semi-bright nickel electroplating. Rinse. Bright nickel electroplating. Rinse. Decorative chromium electroplating. Rinse. In the electroplating steps described above, the metal coating is deposited onto the facebar by applying an electrical potential between the facebar (cathode) and a suitable anode in the presence of an electrolyte. The electrolyte usually consists of a water solution containing a salt of the metal to be deposited and various other additions that contribute to the electroplating process. When the metallic salt dissolves in the water, the metal atoms are freed to move about. The atoms lose one or more electrons and become positively charged ions. The metallic ions are attracted to the negatively charged facebar. They coat the facebar and regain their lost electrons to become metal once again. Typical coating thickness applied to the significant (visible) surfaces of steel facebars is: Total nickel 30 micrometers (1.2 mils) min. Semi-bright nickel Bright nickel Chromium 40-60% of total nickel 40-60% of total nickel 0.25 micrometers (0.01 mils) min micrometers (0.016 mils) max. 3-9

62 3.5.5 Conversion coating During electroplating, the process is tightly controlled to place the required thickness of nickel and chromium on the surfaces with high visibility. The side of a facebar must have excellent appearance and corrosion resistance. Often, a corrosion resistance of 44 hours using the CASS test outlined in ASTM B368 is specified. To avoid unnecessary cost, the electroplating process is designed to place an absolute minimum of nickel and chromium on the hidden surfaces. Phosphate conversion coatings are employed to enhance paint adhesion. By enhancing paint adhesion, they indirectly enhance corrosion resistance. There are several varieties of phosphate coatings (e.g., iron, zinc or manganese). Prior to the application of a conversion coating, the metal surface must be free of shop soils, oil, grease, lubricants and rust. The metal surface must be receptive to the formation of a uniform, adherent chemical film or coating. Surfaces may be cleaned by mechanical methods or, more commonly, by immersion or spray cleaner systems. A phosphate coating is applied by immersing a clean metal part in a hot processing solution for 4-6 minutes, depending on bath chemistry. The weight (thickness) of the conversion coating is dependent on the manner in which the part is cleaned, the immersion time, the composition of the processing bath and the composition of the metal itself Electrocoating (ing) is an organic coating applied by the electrocoating method. Electrocoating has the ability to coat all areas of complex parts including recessed areas and edges. is a durable, lasting coating. It is used as a primer, top coat or both. Parts are usually ed via a conveyor system in one continuous process. Although there are variations, the usual steps in applying to a steel part are: alkaline cleaner, water rinse, surface conditioner, zinc phosphate coating (see Section 3.5.4), rinse, seal coating, de-ionized water rinse, application, permeate rinse, final de-ionized water rinse, and curing oven. ing systems are known as anodic or cathodic depending on whether the part is the anode or the cathode in the electrochemical process. Cathodic systems are common since they require less surface preparation and they provide better corrosion resistance. The process requires a coating tank or bath in which to immerse the part. The bath, containing water and paint, is given a positive charge (cathodic system). The part, with a negative charge, when immersed in the bath, attracts the positively charged paint particles. The paint particles coalesce as a coating () on the part surface. thickness typically applied to bumper beams ranges from 20 to 25 micrometers (0.8 to 1.0 mils). 3-10

63 3.5.7 Paint coating Paint is a cost effective corrosion protection method. It acts as a barrier to a corrosive solution or electrolyte and it prevents, or retards, the transfer of electrochemical charge from a corrosive solution to the metal beneath the paint. Paint is a complex mixture of materials designed to protect the substrate and to enhance appearance. It is composed of binders, carriers, pigments and additives. Binders provide the major properties to the paint while the carriers (solvents and/or water) adjust the viscosity of the paint for the application. Pigments impart specific properties such as corrosion resistance and color. The type of pigment and its volume are critical to the optimization of properties such as adhesion, permeability, resistance to blistering and gloss. Additives include thickeners, flow agents, catalysts and inhibitors. Paints are often identified by the type of polymers employed. Commonly used paint coatings include: Alkyd and epoxy ester (air dried or baked) Two-part coatings such as urethane Latex coatings such as vinyl, acrylic or styrene polymer combinations Water soluble coatings (versions of alkyd, epoxy ester or polyester) Baked enamel basecoat/rigid clearcoat systems are commonly applied to the side of facebars. The process steps include: Conversion coating (see Section 3.5.3) ing (see Section 3.5.4) Enamel basecoating Enamel clearcoating Baking Autodeposition coating Autodeposition is a waterborne process that depends on chemical reactions to achieve deposition. The composition of an autodeposition bath includes a mildly acidic latex emulsion polymer, de-ionized water and proprietary ingredients. The chemical phenomenon consists of the mildly acidic bath attacking the steel parts being immersed and causing an immediate surface reaction that releases iron ions. These ions react with the latex in solution causing a deposition on the surface of the steel parts. The newly deposited organic film is adherent yet quite porous. Thus, the chemical activators can rapidly diffuse to reach the surface of the metal, allowing continued coating formation. The coating thickness is time and temperature related. Initially, the process is quite rapid, but slows down as the film begins to build. As long as the parts being coated are in the bath, the process will continue. Typically, film thickness is from 15 to 25 micrometers (0.6 to 0.8 mils). Autodeposition will coat any metal the liquid touches. Thus, an advantage of this coating is its ability to coat the inside of tubing and deep cavities. Autodeposition does not require a conversion coating and the coating cures at a relatively low temperature. 3-11

64 3.5.9 Powder coating In the powder coating process, a dry powder is applied to a clean object. After application, the coated object is heated, fusing the powder into a smooth continuous film. Powders are available in a wide range of chemical types, coating properties and colors. The most widely used types include acrylic, vinyl, epoxy, nylon, polyester and urethane. Modern application techniques for applying powders fall into four basic categories: fluidized bed process, electrostatic bed process, electrostatic spray process and plasma spray process. The electrostatic spray process is the most commonly used method for applying powders. In this process, the electrically conductive and grounded object is sprayed with charged, non-conducting powder particles. The charged particles are attracted to the substrate and cling to it. Oven heat then fuses the particles into a smooth continuous film. Coating thicknesses in the range of 25 to 125 micrometers (1 to 5 mils) are obtained. 3-12

65 4. Manufacturing considerations 4.1 Forming considerations High-strength and ultra high-strength steels have less ductility, and hence less formability, than lower strength steels. Thus, care must be taken in part design and forming method selection. In addition, springback increases with yield strength and it must be accounted for in the process design. Sections through provide Guidelines and Rules of Thumb for the roll forming and stamping processes. The Guidelines and Rules of Thumb are based on practical experience. Their use will help alleviate formability and springback issues associated with the roll forming and stamping of high-strength and ultra high-strength steels Guidelines for roll forming high-strength steel All of the high-strength steels in Table 2.2 can be roll formed, pre-pierced and swept after roll forming. The following Guidelines apply (Reference 4.3): Do: Select the appropriate number of roll stands for the material being formed. Remember that the higher the steel strength, the greater the number of stands required on the roll former. Use the minimum allowable bend radius for the material in order to minimize springback. Position holes away from the bend radius to help achieve desired tolerances. Establish mechanical and dimensional tolerances for successful part production. Use appropriate lubrication. Use a suitable maintenance schedule for the roll forming line. Anticipate end flare (a form of springback). End flare is caused by stresses that build up during the roll forming process. Recognize that as a part is being swept (or reformed after roll forming), the compression of metal can cause sidewall buckling, which leads to fit-up problems. Don t: Do not roll form with worn tooling, as the use of worn tools increases the severity of buckling. Do not expect steels of similar yield strength from different steel sources to behave similarly. Do not over-specify tolerances. 4-1

66 4.1.2 Guidelines for roll forming ultra high-strength steel. All of the ultra high-strength steels in Table 2.3 can be roll formed, pre-pierced and swept after roll forming. The following Guidelines apply (Reference 6.1): 1. The minimum bend radius should be two times the thickness of the steel to avoid fracture. 2. Springback magnitude can range from ten degrees for 120X steel to 30 degrees for M220HT steel, as compared to one to three degrees for mild steel. Springback should be accounted for when designing the roll forming process. 3. Due to the higher spingback, it is difficult to achieve reasonable tolerances on sections with large radii (radii greater than 20 times the thickness of the steel). 4. Rolls should be designed with a constant radius and an evenly distributed overbend from pass to pass. 5. About 50% more passes (compared to mild steel) are required when roll forming ultra high-strength steel. The number of passes required is affected by the mechanical properties of the steel, section depth-to-steel thickness ratio, tolerance requirements, pre-punched holes and notches. 6. Due to the higher number of passes and higher material strength, the horsepower requirement for forming is increased. 7. Due to the higher material strength, the forming pressure is also higher. Larger shaft diameters should be considered. Thin, slender rolls should be avoided. 8. During roll forming, avoid undue permanent elongation of portions of the cross section that will be compressed during the sweeping process General guidelines for stamping high-strength and ultra high-strength steels. All of the high-strength streels in Table 2.1 may be stamped into bumper beams. Additionally, some ultra high-strength steels in Table 2.2, such as 120X, 590T, 780T and 140T, may be stamped, bend stretched, drawn and flanged. The following guidelines apply (Reference 6.2): PRODUCT DESIGN Avoid designing parts that require a draw forming operation (i.e., metal must flow or stretch off the binder). Maintain gentle shape changes and constant cross sections wherever possible in part design. These factors become more important as material strength is increased. 4-2

67 Keep the depth of the part to a minimum when the part has excessive sweeps in the plan view or elevation. Avoid designing parts with closed corners that require draw die operations. Keep the flanges as short as possible when there is a deep-formed offset flange. DIE PROCESS Try to form the parts completely to the depth desired in the first forming operation. Minimize stretch and compression of metal to reduce residual strains that cause springback and twist in the part. Use high pressure on the draw binder and balancing blocks. They allow the sheet metal to flow without wrinkling. Keep the side walls perpendicular (90 degrees to the base of the die). Avoid open-angle forming. Overbend the flanges 6 to 10 degrees. On straight channel-shaped parts, consider a solid form die. Pre-forming the sheet steel is a method commonly used to accumulate enough material to ensure that adequate metal is available for forming without splitting or excessive thinning. DIE DESIGN Maintain die forming radii as sharp as possible. Try to fold the metal rather then stretch it over a radius. Folding reduces curl of the sidewalls and springback of the weld flanges. Maintain an even draw depth and length of line. Design robust dies to minimize flexing of the die components. DIE CONSTRUCTION / TRYOUT Sidewalls should be as tight as possible to lessen springback. To reduce shock and press tonnage requirements, a minimum shear of four to six times metal thicknesses is required for cutting dies. This minimum shear also reduces noise on break through. Trim and pierce dies should have 7% to 10% die clearance. 4-3

68 FIGURE 4.1 a) RULES OF THUMB - SPRINGBACK 2 The techniques shown in Figures 4.1 a) through 4.1 c) can help compensate for springback when forming a 90-degree bend if a sharp radius or a tight flange (see Figure 4.3) is not adequate. Refer to Figure 4.1a) 1) Restrike the flange at an overbend angle between 3 and 7 degrees, depending on the material strength and/or thickness. 2) Set up part in die to allow for overbend. 3) Undercut the lower die steel and let the metal overbend. 4) Pre-form the top part surface prior to flanging and flatten the part using the die pad. 4-4

69 FIGURE 4.1 b) RULES OF THUMB - SPRINGBACK Refer to Figure 4.1b) 5) The addition of stiffening darts helps maintain a 90-degree flange. 6) Coining a flange radius as the die bottoms will help maintain form and helps prevent springback. 7) An extension of the upper flange steel allows for extra pressure to be applied on the formed radius. This is a difficult process to control, but it could help in special conditions, particularly on heavier gauge steels. 4-5

70 FIGURE 4.1 c) RULES OF THUMB - SPRINGBACK Refer to Figure 4.1c) 8) Providing a vertical step in the flange stiffens and straightens the flange, stopping sidewall curl as well as springback. 9) Rotary benders are used by many manufacturers to control springback, as the metal is rolled around the radius instead of flanging. Positive comments on this method promote its ability to overbend the flange. 10) Place a 90 durometer urethane behind flanging steels in a free state (not compressed). Clearance holes through the flanging steels allow the screws to hold the urethane in place. Please note the urethane must stay 0.25 inches (6.4 mm) off the bottom of the pocket. This space leaves room for the urethane deflection. Tighten clearance until desired effect is achieved. 11) By adding a horizontal step along the flange, the flange is stiffened, resulting in reduced springback. 4-6

71 FIGURE 4.2 RULES OF THUMB - DIE FLANGE STEELS Refer to Figure 4.2 1) Flange steel clearance should be 90% of metal thickness, but no greater than metal thickness. Maintaining a tight condition helps to prevent springback. 2) Because of the tight clearance, the die steels should be as hard as possible. Therefore, it is recommended that air-hardened tool steel or harder material be used, and a surface coating be applied to increase hardness and improve lubricity. 3) Air-hardened tool steel (D2) is recommended for flange steel (Rockwell on the C-scale). However, other materials may be used as long as they have a surface coating applied which resists scoring. 4) All flanging radii should be as sharp as possible without fracturing the sheet metal during forming. The flange radii should be something less than metal thickness. Start by just breaking the sharp corner and work from there until you can make the flange without splitting the sheet metal. 4-7

72 FIGURE 4.3 RULES OF THUMB - HAT SECTION Refer to Figure 4.3 1) Maintain a constant depth on hat sections, if at all possible. 2) The size of the radius is to be kept as small as possible, normally less than metal thickness. 3) Form 90-degree side walls on the hat section whenever possible. 4) If the sidewall is not 90 degrees, try to balance the forming with the same angle on the opposite side of the hat section. 5) Unequal residual strain and/or compression on opposite sidewalls has a tendency to twist the entire rail. 4-8

73 FIGURE 4.4 RULES OF THUMB - RADIUS SETTING When forming a hat section, the action of the die can aid the retention of shape by setting the corner radii. Refer to Figure 4.4 1) As the flange steels make contact with the sheet metal blank, an initial crown is formed. 2) The flange steels then enter over the die-post radii and force the metal to conform to the lower die. The crown remains in the part. It is best if both sides enter simultaneously. 3) The die is now very close to its home position. The crown remains and the lower flanges are starting to form. 4) As the die is closed, the lower flanges are formed with corner radii as sharp as possible. The top corners are forced outward as the crown is hit home by the upper die. If the part retains a crown, then a negative crown can be incorporated to minimize springback. 4-9

74 FIGURE 4.5 a) RULES OF THUMB - COMBINATION FORM & FLANGE DIE Using a combination form-and-flange die is basic to meeting high-strength steel requirements. A general idea of how this die works follows. The die initially forms the contour in the developed blank using the upper pressure pad. The metal is then locked, using the lock beads to prevent feeding the metal in from the ends. The metal is allowed to flow in freely from the sides without restrictions within the ring, just a metal thickness apart to stop wrinkling. The flange steels are maintained as sharp as possible, and the side walls are tight. This procedure controls the springback and sidewall curl in order to produce a quality part. If the part is straight, see Figure 4.4 for more information. The four-piece form and flange die shown above incorporates features that lend themselves to the production of hat section parts. Remember that in order for this type of die to work, the finished part must be off the ring when the part is completely formed in order to avoid upstroke deformation. The unique features of this die are as follows: Refer to Figure 4.5a) 1) The upper pressure pad gives the sheet metal blank its initial contour and holds the blank in location. 2) The lower ring (known also as a lower pressure pad) controls the flow of the metal and prevents wrinkling as the part is being formed (See 5 and 6 on Figure 4.5 b). 4-10

75 FIGURE 4.5 b) RULES OF THUMB - COMBINATION FORM & FLANGE DIE AIR PINS Refer to Figure 4.5a) and Figure 4.5b) 3) Flange steels should be kept tight to the lower post to help prevent sidewall curl. 4) A smaller-than-metal thickness radius on the lower post helps prevent springback. 5) Restraining beads are used to restrain the flow in at the ends of the rail. The metal must flow off the ring and on to the die post to prevent the panel from being deformed by the upstroke of the die. 6) Metal thickness clearance between the upper and lower ring under high pressure is needed to allow the metal to flow in from the sides without buckling. 7) Balancing blocks (leveling blocks, kiss blocks or spacer blocks) are used to control the clearance between the upper form steels and the lower ring surfaces in order to adjust for metal flow. 8) If the rail is open-ended, there is no need to restrict metal flow unless stretch is required to help prevent twist. 4-11

76 FIGURE 4.6 RULES OF THUMB - FORMING BEADS Refer to Figure 4.6 1) Half-round draw beads are used to control metal flow. They restrict the flow and force the metal to stretch or control feed as required to produce the draw shape of the part. 2) Lock beads are generally used to stop the metal from moving. This condition is pure stretch. In general, it is recommended that this type of bead be avoided in dies used to form high-strength steel material. 3) Start lock bead configurations with radii small enough to shear the sheet metal blank. Then uniformly dress the radii to eliminate cutting, but still locking the metal flow. When the beads need reworking, repeat this procedure. 4-12

77 FIGURE 4.7 RULES OF THUMB - FORMING AN EMBOSS When forming an emboss or surface formation into a relatively flat high-strength steel part, the break lines need to be sharp and crisp. You must coin these lines into the part to set them and reduce any springback or distortion. Sidewalls of the embossment must be 45 degrees or less from the surface. Refer to Figure 4.7 1) This formation is totally within the part s perimeter and does not extend to the trim. 2) This example shows the formation open to the part s trim edge. This formation causes excess or loose metal along the edge. Therefore, it is recommended that a short flange and/or small bead be added to stiffen and eliminate this condition. 4-13

78 FIGURE 4.8 RULES OF THUMB - EDGE SPLITTING It is important that the trim quality be maintained to prevent edgesplitting from work hardening. Refer to Figure 4.8 1) When forming an outside corner, the trim edge has a tendency to wrinkle. In order to minimize this wrinkling condition, it is recommended that the flange in the area of the wrinkle be as short as possible. 2) Inside corners have a tendency to split. Therefore, try to make the trim line as long as possible by scalloping the edge. A combination of shortening the flange and lengthening the trim line should help stop the splitting. If not, a formation change has to be made to add material to the split area. 4-14

79 FIGURE 4.9 RULES OF THUMB - PART DESIGN Refer to Figure 4.9 1) The following are general characteristics of high-strength steel (HSS) that should be taken into consideration during the part design phase: HSS will stretch, generally in the range of 2% to 6%. HSS will resist compression due to the hardness of the material. These characteristics of HSS generally require that parts be designed for form and flange die processes rather than draw dies. 2) In some cases, it is necessary to compensate for these material characteristics by designing in darts and/or notches to equalize the length of line and to help maintain part dimensional integrity. 3) The above diagram shows how these darts and notches could be applied to an HSS part. 4-15

80 FIGURE 4.10 RULES OF THUMB - DIE CONSTRUCTION Refer to Figure ) Due to the forces exerted during the forming process of high-strength steel, dies must be built with extra strength. Extra strength is necessary to prevent die flexing. The following are ways to compensate for the unwanted flexing in the die: Block in or heel cam drivers. Use heavy-duty guide pins and bushings. Key in the sections and use large fasteners. Provide for positive returns. Provide heavy-duty die shoes with appropriate reinforcement. 2) Provide for die adjustability during construction. It is important to provide these adjustments because it is undesirable to machine the hardened and coated die details. 3) It is of prime importance to balance the forces exerted on the die during forming. When practical, form two parts at a time, or produce the right and left hand part in the same die. 4-16

81 FIGURE 4.11 RULES OF THUMB - DEVELOPED BLANKS Refer to Figure ) When using high-strength steel material for BIW (Body-In-White) structural parts, testing has demonstrated that the recommended type of forming is with a flange or form die. This type of die utilizes a developed blank. 2) This blank should be as close to finish trim as possible. Only in areas where the trim is critical should a finish trim operation be added. 4-17

82 FIGURE 4.12 RULES OF THUMB - TRIMMING Refer to Figure ) Because high-strength steel (HSS) is more brittle and harder than mild steel, and because it is not as ductile as a result of the strengthening mechanisms in the metallurgy, it is more difficult to trim. HSS requires approximately the same die clearance between the upper and lower trim steels as mild sheet steel. This clearance is approximately 7% to 10% of metal thickness per side. The range of the hardness and the thickness determines the exact amount. 2) Dies must be sharpened more frequently when trimming HSS. They also require rigidity to prevent the die from flexing, which can cause dulling of the trim steels. 3) It is recommended that extremely hard cutting edges be provided on trim steels. Therefore, use of S-7 or other shock-resistant steel with a minimum of Rockwell (C-scale) is recommended. 4-18

83 FIGURE 4.13 RULES OF THUMB - DIE SHEAR Refer to Figure ) Due to excessive shock during blanking or trimming of highstrength steel, a full four times (4x) metal thickness shear is recommended to protect both press and die. In order to prolong the die life of either a blank or trim die, die shear must be added. Advantages of the die shear 1) Lessens tonnage requirements. 2) Saves the press; reduces shock on the press. 3) Lengthens the die life between tune-ups and sharpening. 4-19

84 4.1.4 Guidelines for hat sections stamped from high-strength or ultra high-strength steels. Basic guidelines for designing and processing hat section parts of high-strength or ultra high-strength steel are (Reference 6.3): Do: Form channels as close to finished shape as possible. Avoid closed ends on channels. Utilize small die radii. A combination of low pad pressure and tight clearance minimizes curl and springback. Allow for extra development time. Don t: Assume high-strength and ultra high-strength steel will behave like mild steel. Depend on traditional die design criteria Rules of Thumb for high-strength steel stampings. Common concerns associated with the use of high-strength steel in a stamping operation include springback, splitting, tolerances, die design, die life and blank design. The automotive industry routinely produces stamped high-strength steel parts. Over the past several years, many lessons have been learned through extensive practical experience. These lessons have been summarized in the form of Rules of Thumb in Figures 4.1 through 4.14 (Reference 6.2). The application of the Rules of Thumb will alleviate issues associated with high-strength steel at the part design and die design stages. They will shorten die development time and help ensure production success in the stamping of high-strength steel parts. 4.2 Welding considerations High-strength and ultra high-strength steels are routinely welded on a production basis. Most assemblies can be welded with conventional equipment using weld cycles similar to conventional ones. In most applications, high-strength or ultra high-strength steel is welded to mild steel using gas metal arc or high-frequency welding. When welding ultra high-strength steels, specific weld windows should be developed. With nominal modification to standard weld procedures, weight reduction may be achieved with high-strength and ultra highstrength bumper beam assemblies. 4-20

85 4.2.1 Steel chemistry High-strength and ultra high-strength steels Welding processes Welding procedures must suit the chemistry of the steel grade being welded. Steel specifications traditionally set limits on the main elements in a steel grade (e.g., carbon, manganese). However, most steel grades contain additional elements that have not been specified. Thus, when selecting suitable welding procedures, it is important to identify the levels of any unspecified elements in a bumper steel grade. Recommended Practice, SAE J2340 (Reference 6.4), recognizes this fact and places limits on unspecified elements. The high-strength and ultra high-strength steels covered by SAE J2340 are shown in Table 4.1. The unspecified elements permitted in the SAE J2340 grades are shown in Table 4.2. When welding high-strength and ultra high-strength steels, it is important to consider several factors usually not considered when welding low-strength steels (e.g., welding process, welding parameters and material combinations). Integration of these considerations can result in a successful welding system. For instance, a low heat input resistance seam welding method has been successfully employed for commercial production of bumper beams made from M190HT steel. Various welding methods (arc welding, resistance welding, laser welding and high-frequency welding) all have unique advantages for the welding of specific sheet steel combinations. Factors such as production rate, heat input, weld metal dilution and weld location access may make one welding system more desirable than another system. For instance, a high-strength steel that is problematic for spot welding may not exhibit the same difficulty in arc or highfrequency welding. It is important to consider material combinations when employing welding processes that solidify from a molten pool, or that are constrained by thickness ratio. In general, caution should be exercised when spot welding a high-strength or ultra high-strength steel to itself because of possible weld metal interfacial fracture tendencies. However, even a problematic higher strength steel can be spot welded to a mild steel. On behalf of the Bumper Project of the American Iron and Steel Institute, David Dickinson, The Ohio State University, conducted a survey on bumper component welding (Reference 4.5). The survey identified the welding processes that are currently used in bumper manufacturing, or were used to produce prototype bumpers. The processes are: 1. Gas metal arc welding (GMAW) 2. Flux cored arc welding (FCAW) 3. Resistance spot welding (RSW) 4. Resistance projection welding (RPW) 5. Resistance seam welding (RSeW) 6. Resistance projection seam welding (RPSeW) 7. High frequency and induction resistance seam welding (RSeW-HF&I) 8. Upset welding (UW) 9. Friction welding (FRW) 10. Laser beam welding (LBW) 11. Laser beam and plasma arc welding (LBW/PAW) A brief description of each welding process is given in Sections to

86 TABLE 4.1 SAE J2340 STEELS AND STRENGTH GRADES Steel Description Grade Type Available Strength Grade - MPa Dent Resistant Non Bake Hardenable A 180, 210, 250, 280 Dent Resistant Bake Hardenable B 180, 210, 250, 280 High-Strength Solution Strengthened S 300, 340 High-Strength low-alloy X & Y 300, 340, 380, 420, 490, 550 High-Strength Recovery Annealed R 490, 550, 700, 830 Ultra High-Strength Dual Phase DH & DL 500, 600, 700, 800, 950, 1000 Ultra High-Strength Low Carbon Martensite M 800, 900, 1000, 1100, 1200, 1300, 1400, 1500 TABLE 4.2 SAE J2340 CHEMICAL LIMITS ON UNSPECIFIED ELEMENTS Maximum Percent Allowed Element Type A, B & R Type S Type X & Y Type D & M P S Cu Ni Cr Mo Notes: 1) P= phosphorus S= sulphur Cu= copper Ni= nickel Cr= chromium Mo= molybdenum 2) Maximum phosphorus shall be less than on grades 180A & 180B. 3) The sum of Cu, Ni, Cr and Mo shall not exceed 0.50% when of these elements are specified. When one or more of Cu, Ni, Cr or Mo are specified, the sum limit of 0.50% does not apply. However, the individual limits for the unspecified elements apply. 4-22

87 Gas metal arc welding (GMAW) This process, schematically illustrated in Figure 4.15a), utilizes a direct current electrical power supply with the electrode positive (DCEP). The positive electrode attracts electrons flowing in the circuit. The electrons act to melt the electrode wire that deposits within the weld metal, mixing with molten material from the base metal. Shielding to prevent oxidation of the hot wire and molten weld pool region is provided by an inert shielding gas directed into the weld region by the gas nozzle. The consumable electrode material is selected to match the strength (and other important characteristics) of the base metal. The wire guide and contact tube must be periodically replaced in order to maintain good electrical contact. Also, the gas nozzle must be occasionally cleaned of spattered material. The welding current is varied by changing the wire feed speed. Higher wire feed speeds produce higher welding currents. The arc length can be varied by changing the voltage setting. Higher voltages produce longer arcs. As illustrated in Figure 4.15b), there are four basic methods in which the wire is transferred to the molten weld pool: short-circuiting, globular, pulsed spray and spray transfer. These transfer modes have been used to describe the GMAW process itself. Terms such as short arc, dip transfer MIG and spray are all common non-standard terms used to describe the GMAW process and the mode of operation. Short-circuiting transfer characteristics At low current and voltage, short circuit transfer occurs. The weld is a shallow, penetrating one with low heat input. Using GMAW in this mode allows welding in all positions since the weld puddle is small. In comparison to the other three modes of transfer, this method is slowest (low productivity). This mode produces large amounts of spatter if welding variables are not optimized. This mode, also know as short arc or dip transfer, is used primarily for sheet metal applications. Globular transfer characteristics This mode of transfer is obtained at intermediate current and voltage levels or at high current and voltage levels with 100% CO 2 shielding gas. It has higher heat input and penetration than short circuit transfer. A larger weld pool makes it more difficult to weld in the over-head position. It produces significant amounts of spatter. Pulsed spray and spray transfer characteristics Spray is achieved at higher welding current and voltage with argon or helium based shielding gas (over 80%Ar). This high-heat, deep-penetrating weld limits the application to the flat position. This mode produces little or no spatter and is known for the high deposition rate (higher productivity). Pulsing the current where spray transfer occurs allows for better control for out-of-position welding. 4-23

88 FIGURE 4.14 GAS METAL ARC WELDING (GMAW) a) SCHEMATIC b) METHODS OF WIRE TRANSFER c) EFFECT OF SHIELDING GAS 4-24

89 In GMAW, the shielding gas (used for atmospheric shielding) also affects the type of metal transfer in the process, penetration depth, and the bead shape. These factors are schematically illustrated in Figure 4.14c). The ionization potential of the gas is the ability of the gas to give up electrons and is the characteristic that determines the plasma characteristics of the arc. The ionization potential (IP) of the gas can have an effect on welding characteristics such as arc heat, stability, & starting: Helium, with high ionization potential, inhibits spray transfer in steels. CO 2, with moderate ionization potential also has limited spray transfer. Argon, with low IP, promotes the spray mode - particularly at higher currents. Surface tension of the weld pool and metal droplets are also affected by the type of shielding gas. Surface tension affects: The drop size. Puddle flow. Spatter Argon results in high surface tension with shallower penetration. CO 2 results in low surface tension with deeper penetration. The advantages and limitations of GMAW are: Advantages High deposition rates High Productivity No slag removal Continuous welding Easily automated Joint fit-up tolerance Limitations Equipment is more expensive and complex than some manual welding processes Process variants/metal transfer mechanisms make the process more complex and the process window more difficult to control Restricted access (the GMAW gun is larger than other electrode holders) Spatter Porosity (especially with coated materials) Higher heat input than some processes In summary, the GMAW process is ideally suited for many bumper beam applications because of its high deposition rate that results in high weld productivity. It is a process that is used on automated and continuous welding lines and is often linked with robots and robotic manufacturing cells. It is tolerant to moderate joint misalignment and thus is suited for welding materials that might experience some forming springback. It is a relatively clean process requiring no slag removal from the weldment as do other types of welding processes. It requires only occasional tip and gas cap maintenance. 4-25

90 Flux cored arc welding (FCAW) GMAW equipment is more expensive than most manual welding equipment. The complexity of process variants makes process control more difficult, thus requiring experienced personnel. The weld gun may have difficulty reaching into restricted spaces; thus, design of parts and supplemental machinery must be considered. Spatter and porosity discontinuities may occur if process parameters are not fairly accurately controlled, leading to the need for weldment inspection and possibly clean up and post weld repair. Finally, heat input may need to be controlled, particularly when welding high-strength and ultra high-strength bumper steels. A useful reference document for GMAW is ANSI/AWS/SAE Specification for Automotive and Light Truck Component Weld Quality - Arc Welding (Reference 6.7). As illustrated in Figure 4.15a), FCAW uses a tubular wire that is filled with a flux. The arc is initiated between the continuous wire electrode and the workpiece. The flux, which is contained within the core of the tubular electrode, melts during welding, supplying some cleaning action for the weld metal. It resolidifies as a slag behind the weld shielding the hot weld from oxidation. Vapor formant materials, contained in the flux core, decompose and additionally shield the weld pool from the atmosphere. Direct current, electrode positive (DCEP) is commonly employed as the FCAW process. There are two basic variants of the FCAW process as shown in Figure 4.15b): 1. Self-shielded (without shielding gas). 2. Gas-shielded (with shielding gas). Each variant uses different agents in the flux core. Usually, selfshielded FCAW contains significant quantities of gas forming powder that make this variant useful in outdoor conditions where wind would blow away a shielding gas. The fluxing agents in self-shielded FCAW are designed not only to shield the weld pool and metal droplets from the atmosphere, but also to deoxidize the weld pool. In gas-shielded FCAW, supplemental shielding gas is provided. Thus, the flux generates only a secondary source of gas shielding from the atmosphere. The main role of the flux is to support the weld pool for out-of-position welds. Gas-shielded FCAW is often used to increase the productivity of out-of-position welding and to achieve deeper penetration welds. The advantages and limitations of FCAW are: Advantages High deposition rates Deep penetration High-quality Less pre-cleaning than GMAW Slag covering helps with larger out-of-position welds Self-shielded FCAW is draft tolerant Limitations Slag must be removed More smoke and fumes than GMAW Spatter FCAW wire is expensive Equipment is more expensive and complex than that for manual welding 4-26

91 FIGURE 4.15 FLUX CORED ARC WELDING (FCAW) a) SCHEMATIC b) PROCESS VARIANTS (Reference 4.6) 4-27

92 Resistance spot welding (RSW) In summary, the FCAW process offers deeper penetration and higher deposition rates than the GMAW process, particularly in out-of-position welds. Perhaps one of the most important advantages of FCAW, particularly in bumper welding, is a tolerance for material that has not been rigorously cleaned as the flux aids in the cleaning operation during welding. However, slag must be removed from the weldment, and smoke must be removed from the manufacturing environment. If weld parameters are not set properly, spatter on the weldment may become a problem. A useful reference document for FCAW is ANSI/AWS/SAE Specification for Automotive and Light Truck Component Weld Quality Arc Welding (Reference 6.7). Resistance spot welding is the most common of the resistance welding processes. It is used extensively in the automotive, appliance, furniture, and aircraft industries to join sheet materials. In this process, water-cooled, copper electrodes, as illustrated in Figure 4.16a), are used to clamp the sheets to be welded into place. The force applied to the electrodes insures intimate contact between all the parts in the weld configuration. A current is then passed across the electrodes through the sheets. The contact resistances, which are relatively high compared to the bulk material resistance, cause heating at the contact surfaces. The combination of heat extraction by the chilled electrodes and rapid contact surface heating causes the maximum temperature to occur roughly around the faying surface. As the material near the faying surface heats, the bulk resistance rises rapidly while the contact resistance falls. Again, the peak resistance is near the faying surface, resulting in the highest temperatures in that region. Eventually melting occurs at the faying surface, and a molten nugget develops. On termination of the welding current, the weld cools rapidly under the influence of the chilled electrodes and causes the nugget to solidify, joining the two sheets. Acceptable-sized weld nuggets can be produced over a range of currents as illustrated in the operating window or lobe curve presented in Figure 4.16b). At the lower end of the current range is the minimum nugget size, which can be found in a resistance-welding manual and is based on the diameter of the electrode face. At the upper end of the current range is the expulsion limit. Expulsion is a condition in which the weld nugget grows to a size that cannot be contained by the electrode force; molten metal bursts out of the weld seam. The current range over which an acceptable nugget size is obtained is a measure of the robustness of the welding process. A wide current range indicates that significant variations in the process can occur while maintaining some minimum weld quality. A narrow range, on the other hand, indicates that minor variations in process conditions can result in unacceptable weld quality. The lobe curve graphically represents the range of acceptable welding currents as a function of welding time. The minimum and expulsion currents are determined for a number of welding times at a particular electrode force. Separate lines are drawn to connect the minimum weld size currents and the expulsion currents. The required current level for making a consistently sized weld (presumably just below expulsion) is probably the simplest method of defining weldability. This measure of weldability is an indication of the size of welding transformers required to weld the materials of interest. 4-28

93 FIGURE 4.16 RESISTANCE SPOT WELDING (RSW) a) SCHEMATIC b) LOBE CURVE FIGURE 4.17 RESISTANCE PROJECTION WELDING (RPW) SEQUENCE OF PROJECTION COLLAPSE 4-29

94 The advantages and limitation of RSW are: Advantages Limitations High speed, (<0.1 Higher equipment costs than arc seconds in automotive welding spot welds) Surface indentation Excellent for sheet Nondestructive testing metal applications Low tensile and fatigue strength [thickness <6.4 mm Not portable (0.25 inches)] Electrode wear No filler metal Lap joint requires additional metal RSW is widely used in bumper manufacturing because of its high speed and excellent adaptability for sheet materials. However, RSW requires a sizable investment in equipment and the equipment is mostly non-portable. RSW welds are difficult to inspect nondestructively and they often have lower tensile and fatigue properties than the base metal. Well-maintained electrodes are required to ensure the highest quality spot-welds. In addition, surface indentations are often observed at the location where the welds are made. In many applications these are not objectionable. However, in cases where surface appearance is critical, the resistance projection welding process should be used. Two useful references on the evaluation of resistance spot welds are the Weld Quality Test Method Manual published by the Auto/Steel Partnership (Reference 6.5) and the ANSI/AWS/SAE Standard Recommended Practices for Test Methods for Evaluating the Resistance Spot Welding Behavior of Automotive Sheet Steel Materials (Reference 6.6). It should be noted that these standard test methods are intended for yield strengths up to 420 MPa (60.9 ksi) and modifications may be required for higher yield strengths Resistance projection welding (RPW) RPW, as illustrated in Figure 4.17, is a variation on resistance spot welding. Basically, a protrusion (projection) is placed on one of the two materials to be welded. This projection is then brought into contact against the second material. The welding sequence is similar to that for resistance spot welding. The welding electrodes are used to apply both force and current across the configuration. The projection constricts current flow (It is a point of high resistance in the welding circuit, and heating occurs preferentially at this point). As the material heats, it becomes soft, and the projection collapses under the force applied by the welding electrodes. Due to the amount of plastic flow involved, melting is not always necessary to form a sound weld. The sequence of events during the formation of a projection weld is shown in Figure In illustration (a), the projection is shown in contact with the mating sheet. In illustration (b), the current has started to heat the projection to welding temperature. The electrode force causes the heated projection to collapse rapidly and fusion takes place as show in illustration (c). The completed weld is shown in illustration (d). 4-30

95 Projection welding is not limited to sheets. Any joint whose projection (contact area) is small compared to the thickness of the parts being welded is a candidate for projection welding. The purpose of a projection is to localize the heat and pressure at a specific location in a joint. The projection design determines the current density required. Projections in sheet metal parts are generally made by embossing, as opposed to projections in solid metal pieces that are made by either machining or forging. In the case of stamped parts, projections are generally located on the edge of the stamping. The advantages and limitations of RPW are: Advantages Limitations Satisfactory heat Requires an additional operation to balance for welding form projections difficult combinations Requires accurate control of projection Uniform results height and precise alignment of the Increased output welding dies with multiple welds because welds are Requires higher capacity equipment being made than spot welding simultaneously Sheet metal thickness limited by ability Longer electrode life to form projections Welds may be closely spaced Parts easily welded in assembly fixture Improved surface appearance Parts welded that cannot be resistance spot welded RPW offers significant production advantages. The welding electrodes are flat and contact a large surface area on the parts being joined. Also, electrode life is improved and the electrodes require less attention and maintenance that those used in resistance spot welding. In resistance spot welding, if the welds are too closely spaced, the welding current is shunted through a previously finished weld. In RPW, multiple welds may be made simultaneously. Thus, shunting is less of an issue and welds may be more closely spaced than in resistance spot welding. However, if more that three projections are welded simultaneously, the height of the projections must be uniform to avoid some projections fusing before others have made contact. Alternately, ample pressure in conjunction with a double weld cycle (one schedule) may be run. The first weld should be short in time and high in current. The first hit buries and evens out the projections. The second weld should be longer in time and lower in current. The second hit tempers the welds. In conventional spot welding, parts may be located by an assembly fixture and moved to make a second or third spot-weld. When using projection welding, the parts are simply placed in a nest and, with one operation of the machine; all welds are made at once. One part may be located in relation to the other by punching holes in one and matching them with semi-punchings from the other. 4-31

96 Resistance seam welding (RSeW) Small parts, such as brackets or handles, are difficult to locate in a spot welding machine, which results in misplaced spots or extruded metal. Neat embossing would be less unsightly and a fitted electrode would not mark the exposed surface. RPW has some limitations. The formation of projections may require an additional operation unless the parts are press-formed to design shape. With multiple welds, accurate control of projection height and precise alignment of the welding dies are necessary to equalize the electrode force and welding current. With sheet metal, the RPW process is limited to the thickness in which projections with acceptable characteristics can be formed. RSeW is a variation on resistance spot welding. In this case, the welding electrodes are motor driven wheels, which produce a rolling resistance or seam weld. There are three independent parameters: power supply and control, welding wheel configuration and sheet configuration. Power supply and control governs the frequency with which current is applied to the workpiece. Depending on this frequency and the speed with which the material is being welded, the weld will be a continuous seam weld, an overlapping seam weld or a roll spot weld as illustrated in Figure 4.18a). Seam welds are typically used to produce continuous gas-tight or liquid-tight joints in sheet assemblies, such as automotive fuel tanks. The process is also used to weld longitudinal seams in structural tubular sections such as bumper beams. In fuel tanks, the use of overlapping or continuous seam welds is mandatory. However, bumper beams do not require leak-tight seams and roll spot welds may be used. Typical lobe curves for RSeW are presented in Figures 4.18b) and c)(reference 4.7). The major variables that control the quality of seam welds are current (impulse or continuous), speed and force. These variables are plotted for both uncoated and hot-dip galvanized steels. It can be noted that as the speed increases, a limit is reached where a non-continuous seam is produced. Likewise, as the current is increased, a point is reached where surface eruptions or expulsion occurs and the copper from the electrodes melts and may cause additional cracking. In general, increased electrode force tends to increase the acceptable lobe size and move it to higher current levels. For coated steels, the speed tends to be reduced and the current increased. The advantages and limitations of RSeW are: Advantages Limitations High Speed Higher equipment costs than arc welding Excellent for sheet Power line demands metal applications Nondestructive testing [<6.35mm Low tensile and fatigue strength (0.25 inches)] Not portable No filler metal Electrode wear Ability to produce Lap joint requires additional metal leak-tight joints 4-32

97 FIGURE 4.18 RESISTANCE SEAM WELDING (RSeW) Surface Eruption, Cu Contamination Cracking Lower Speed Higher Current CURRENT, ka Non-Continuous Seam CURRENT, ka Units as per b FORCE N FORCE lb. SPEED, in./min. SPEED, mm/sec a) SEAM VARIATIONS b) LOBE CURVE FOR UNCOATED LOW CARBON STEEL FORCE N FORCE lb. SPEED, in./min. SPEED, mm/sec c) LOBE CURVE FOR HOT-DIP GALVANIZED LOW CARBON STEEL FIGURE 4.19 RESISTANCE PROJECTION SEAM WELDING (RPSeW) a) SCHEMATIC b) SEAM GEOMETRY 4-33

98 Resistance projection seam welding (RPSeW) The advantages of high speed, applicability to sheet materials and no need for filler metal make RSeW ideally suited for the closure welding of bumper beam tubes in a high speed automated fabrication line. Often these lines consist of a steel coil (slit to the proper width) being fed from a pay-off reel into a continuous roll forming line. The line forms the required tubular cross section. The seam welder then closes the open tube. The formed and welded tubular section may then go through an induction heat-treating device or into a sweep forming device, and finally into a cutter, which cuts the beam to length. The limitations of RSeW include higher initial equipment costs compared to arc welding and higher power costs compared to arc welding. In addition, electrode wear and maintenance and the lack of non-destructive testing techniques to assure good welds must be addressed. Finally, because RSeW is suited to lap joints (rather than butt joints as used in arc welding), a slight increase in part weight occurs. In conventional projection welding (RPW), the current is concentrated exactly at the weld location. A relatively new process, resistance projection seam welding as illustrated in Figure 4.19a), does the same thing in seam welding (Reference 4.8). In RSeW, a projection is rolled into one of the sheets to be welded on a roll forming line. The sheet with the projection, and the sheet to which it is to be welded, are presented into the resistance seam-welding machine where current is passed through two opposed rolls. The current must flow through the projection thus concentrating its density as in conventional projection welding. The shape of the projection has been studied and both the continuous projection geometry and the dimple projection geometry (as illustrated in Figure 4.19b), have been successfully used. The continuous projection makes a continuous weld, but requires more total energy input. The dimple projection makes an intermittent seam; but requires less total energy input. The advantages and limitations of RPSeW are: Advantages Satisfactory heat balance for welding difficult combinations Uniform results Reduced total energy consumption Longer electrode life Parts easily welded in assembly fixture surface Improved surface appearance Parts welded that cannot be resistance spot welded Limitations Requires an additional operation to form projections Requires accurate control of projection height and precise alignment of the welding dies Sheet metal thickness limited by ability to form projections 4-34

99 The advantages of RPSeW are: heat balance problems are solved, the welds are uniform, welding speed is increased and total energy consumption is reduced. The preparation of the projection, however, requires an additional step. This issue may not be too great a concern if the projection is formed on the same roll forming line used to make a part. However, control of the projection size and design is still an issue High frequency and induction resistance seam welding (RSeW - HF&I) High frequency welding includes those processes in which the coalescence of metals is produced by the heat generated from the electrical resistance of the work to high frequency current, usually with the application of an upsetting force to produce a forged weld. There are two processes (Reference 4.9) that utilize high frequency current to produce the heat for welding: high frequency resistance welding (HFRW), as illustrated in Figure 4.20a), and high frequency induction welding (HFIW), sometimes called induction resistance welding, as illustrated in Figure 4.20b). The heating of the work in the weld area and the resulting weld are essentially identical with both processes. With HFRW, the current is conducted into the work through electrical contacts that physically touch the work. With HFIW, the current is induced in the work by coupling with an external induction coil. There is no physical electrical contact with the work. A characteristic of high frequency current is that it travels as close to the vee edge as possible, thus treating only the surfaces that are to be welded. Although the welding process depends upon the heat generated by the resistance of the metal to high frequency current, other factors must also be considered for successful high frequency welding. Because the concentrated high frequency current heats only a small volume of metal (just where the weld is to take place), the process is extremely energy efficient, and welding speeds can by very high. Materials handling, forming and cutting limit the maximum line speed. Minimum line speed is set by material properties and weld quality requirements. The fit of the surfaces to be joined and the manner in which they are brought together is important if high-quality joints are to be produced. Flux is not usually used but can be introduced to the weld area in an inert gas stream. Inert gas shielding of the welding area is generally needed only for joining reactive metals such as titanium and certain stainless steel products. The advantages and limitations of high frequency welding processes are: Advantages Produces welds with very narrow heataffected zones High welding speed and low power consumption Able to weld very thin wall tubes Minimizes oxidation and discoloration as well as distortion Limitations Special care must be taken to avoid radiation interference in the plant s vicinity Uneconomical for products required in small quantities Needs proper fit-up Hazards of high frequency current 4-35

100 FIGURE 4.20 HIGH FREQUENCY AND INDUCTION RESISTANCE SEAM WELDING (RSeW-HF&I) a) HIGH FREQUENCY RESISTANCE WELDING b) HIGH FREQUENCY INDUCTION WELDING FIGURE 4.21 UPSET WELDING (UW) a) SCHEMATIC b) PLATEN MOTION 4-36

101 High frequency welding processes offer several advantages over low frequency and direct current resistance welding processes. One characteristic of the high frequency processes is that they can produce welds with very narrow heat-affected zones. The high frequency welding current tends to flow only near the surface of the metal because of the skin effect and along a narrow controlled path because of the proximity effect. The heat for welding, therefore, is developed in a small volume of metal along the surfaces to be joined. A narrow heat-affected zone is generally desirable because it tends to give a stronger welded joint than the wider zone produced by many other welding processes. With some alloys, the narrow heat-affected zone and absence of cast structure may eliminate the need for post-weld heat treatment to improve the metallurgical characteristics of the welded joint. The shallow and narrow current flow path results in extremely high heating rates and therefore, high welding speeds and low-power consumption. A major advantage of the continuous high frequency welding processes is their ability to weld at very high speeds. high frequency welding can also be used to weld very thin wall tubes. Wall thicknesses down to 0.13mm(0.005 inches) is presently being welded on continuous production mills. The processes are adaptable to many steels including low carbon, low-alloy and stainless steels. Because the time at welding temperature is very short and the heat is localized, oxidation and discoloration of the metal as well as distortion of the part are minimal. As with all processes, there are limitations. Because the equipment operates in the radio frequency range, special care must be taken in its installation, operation, and maintenance to avoid radiation interference in the plant s vicinity. As a general rule, the minimum speed for carbon steel is about 7.6m/min(25 feet/min). For products that are only required in small quantities, the high frequency processes may be uneconomical unless the technical advantages justify the application. Because the high frequency processes utilize localized heating in the joint area, proper fit-up is important. Equipment is usually incorporated into mill or line operation and must be fully automated. The process is limited to the use of coil, flat, or tubular stock with a constant joint symmetry throughout the length of the part. Any disruption in the current path or change in the shape of the vee can cause significant problems. Special precautions must be taken to protect plant personnel from the hazards of high frequency. The high frequency processes have found applications in the seam welding of bumper reinforcement beams on continuous lines. 4-37

102 Upset welding (UW) UW is a resistance welding process that produces coalescence over the entire area of faying surfaces, or progressively along a butt joint, by the heat obtained from the resistance to the flow of welding current through the area where those surfaces are in contact. Usually DC current is used for the heating, with the parts clamped in electrical contacting dies, one stationary and the other movable as illustrated in Figure 4.21a). Pressure is used to complete the weld. The movable clamping die (or platen motion) is presented in Figure 4.21b). At first, the motion brings the parts into intimate contact. Then the weld current is energized. In joints with normal fit-up, some thermal expansion may be seen as the parts heat. Joints with poor fit-up tend to experience a joint seating motion during this period. At a point in time when sufficient heating has occurred, a rapid forging force is applied and the abutting parts are rapidly forced into each other, causing some outward material flow. With this process, welding is essentially done in the solid state. The metal at the joint is resistance heated to a temperature where recrystallizaion can rapidly take place across the faying surfaces. A force is applied to the joint to bring the faying surfaces into intimate contact and then upset the metal. Upset hastens recrystallization at the interface and, at the same time, some metal is forced outward from this location. This tends to purge the joint of oxidized metal. Upset welding has two variations: 1. Joining two sections of the same cross section end-to-end (butt joint). 2. Joining of sections with differing cross sections such as a stud to a plate. The first variation can also be accomplished by flash welding. The second variation is also done with resistance projection welding. The advantages and limitations of UW are: Advantages Limitations Some flexibility in Produces unbalance on three-phase cross section shape primary power lines so often DC Rapid process, can current is used be automated Requires special equipment for Impurities can be removal of flash metal removed during Difficult alignment for workpieces upset with small cross sections Can weld rings and Requires part cross section various cross sections consideration The upset welding of butt joints is fast and can be automated. There is some flexibility in joint design. However, control of the joint tolerances is critical. The process requires large amounts of current so DC rectified current is usually used to improve efficiency. In some applications, the weld flash must be removed. The upset butt process involves relatively slow heating and no measures are taken to protect the joint from air. Consequently, a generous upset is required to exude oxidized metal. For this reason, other butt welding processes such as flash, percussion or friction welding are often preferred. 4-38

103 Friction welding (FRW) FRW is a process that produces a weld under a compressive force (Reference 4.10). As illustrated in Figure 4.22a), the work pieces are brought into contact and rotated very rapidly to produce heat. Usually one piece is rotated against a stationary piece to produce the heat at the junction. The rotation time and force are adjusted until the temperature in the joint reaches the forging temperature of the material at which time the rotation is stopped and an axial force is applied to forge weld the pieces together. As such, the process is a solid-state bonding process. Geometries that have a rotational symmetry are particularly suitable for friction welding. Applications include round bars and tubes to each other, as well as bars or tubes to sheet steel. Linear friction welding is used for parts with non-rotational symmetry. In this application, one part is oscillated back and forth against the other (Figure 4.22b). The advantages and limitations of FRW are: Advantages Faster than most other processes Can join dissimilar material together (e.g.) Copper to steel Easily automated for high-volume production Limitations Start-up cost is high Parts must be able to rotate about an axis of symmetry Free machining alloys are difficult to weld Non-forgeable materials cannot be friction welded Laser beam welding (LBW) FRW is fast and can join many different materials. It is one of only a few welding processes that has this material variability. It is easily automated. However, part geometry can be a limitation; and, in general, the materials to be joined must be hot forgeable. LASER is an acronym for light amplification by stimulated emission of radiation. A laser beam that becomes highly focused is an excellent source of concentrated energy. This energy is used for many welding applications and also for cutting and heat treating. Two basic types of lasers are used in welding: solid-state and gas (Reference 4.10). Solid-state lasers are made of a single elongated crystal rod. Nd:YAG (a doped crystal of neodymium with yttrium, aluminum, and garnet) is the most common solid-state laser used for welding today. The end surfaces of the rod are ground flat and parallel. These ends usually have a reflectiving placed on them. While one end is totally reflective, the other end is partially reflective, leaving a small area for photons to escape. The Nd ions excite their electrons to a higher energy level. By doing this, photons are emitted at a wavelength of 1.06 microns. After the photons are emitted, the electrons are allowed to return to their original state. 4-39

104 FIGURE 4.22 FRICTION WELDING (FRW) a) PART ROTATION b) PART OSCILLATION FIGURE 4.23 LASER BEAM WELDING (LBW) a) CARBON DIOXIDE LASER b) BEAM FOCUS 4-40

105 The most common gas laser is the carbon dioxide laser (see Figure 4.23a). It is also the laser used for most welding applications. An electrical charge excites the carbon dioxide molecules, which on their return to their normal energy state emit some photons. Much like solid-state lasers, reflective surfaces are placed at the ends of the tube in which the gas is contained. The one end is totally reflective, while the other allows a small amount of light to pass. This light is emitted at a wavelength of 10.6 microns. Factors affecting the choice between gas and solid-state lasers are: Nd:YAG lasers: most metals absorb its wavelength better than the CO 2 laser wavelength, versatile fiber-optic delivery, easy beam alignment, easier maintenance, smaller equipment, and more expensive safety measures than CO 2 because of its wavelength. CO 2 lasers: higher power, better beam quality in terms of focus ability, higher speeds and deeper penetration for materials that don t reflect its light, and lower start-up and operation. In laser welding, the beam can be focused for different applications as illustrated in Figure 4.23b). Usually, a small focus size is used for cutting and welding, while a larger focus is used for heat treatment or surface modification. The focal spot of the beam can also be varied based on the application. The advantages and limitations of LBW are: Advantages Limitations Single pass weld High initial start-up costs penetration in Part fit-up and joint tracking are steel up to 19mm critical (0.75 inches) thick Not portable Materials need High cooling rates may lead to not be conductive material problems No filler metal required Low heat input produces low distortion LBW advantages include the very rapid weld travel speed and the low heat input that results in very little distortion. However, initial equipment costs for laser welding are high. Additional costs to assure good part fit-up may be of some disadvantage. Coatings on steel can be a problem in plume formation through which the laser beam cannot adequately penetrate. Fume control shielding gas may be required Laser beam and plasma arc welding (LBW/PAW) There have been a number of experimental developments in welding processes using the laser welding process as a base and coupling a second welding process (such as plasma arc welding) with it. The benefit is that the high travel speed associated with the laser process is combined with the metal fill, the less stringent part fit-up and the favorable bead shape associated with the plasma arc process. Two variations of the LBW/PAW process are described in two patents (References 4.11 and 4.12). 4-41

106 4.2.4 Weldability of bumper materials The heat of welding causes changes in the microstructures and mechanical properties in a region of heated steel that is referred to as the heat-affected zone (HAZ). The resulting microstructure in the HAZ will depend on the composition of the steel and the rate at which the steel is heated and cooled. The degree of hardening in the HAZ is an important consideration determining the weldability of a carbon or low-alloy steel. Weldability and resistance to hydrogen cracking generally decrease with increasing carbon or martensite in the weld metal or the HAZ, or both. Although carbon is the most significant alloying element affecting weldability, the effects of other elements can be estimated by equating them to an equivalent amount of carbon. Therefore, the effect of total alloy content can be expressed in terms of a carbon equivalent (CE). One empirical formula that may be used for judging the risk of underbead cracking in carbon steel is: CE = C + Mn + Cr + Mo + V + Ni + Cu Generally, steels with low CE values (e.g., 0.2 to 0.3) have excellent weldability; however, the susceptibility to underbead cracking from hydrogen increases when the CE exceeds Ranking of welding processes David Dickinson, The Ohio State University, used his experience and the results of a State-of-the-Art Welding Survey (Reference 4.5), to rank the suitability of various welding processes for joining bumper steels. His poor, acceptable, better and best rankings are given in Table 4.3. Note: The rankings for 10B21 Modified were added to the Table by the American Iron and Steel Institute s Bumper Project Group. The rankings are subjective and should not be taken as absolute. However, they do provide a starting point for the selection of a welding process. The welding processes in Table 4.3 were all identified in Dickinson s SOA Survey as ones that are currently used in bumper manufacture, or were used to produce prototype bumpers. The processes, described in Sections to , are: 1. Gas metal arc welding (GMAW) 2. Flux cored arc welding (FCAW) 3. Resistance spot welding (RSW) 4. Resistance projection welding (RPW) 5. Resistance seam welding (RSeW) 6. Resistance projection seam welding (RPSeW) 7. High frequency and induction resistance seam welding (RSW-HF&I) 8. Upset welding (UW) 9. Friction welding (FRW) 10. Laser beam welding (LBW) 11. Laser beam and plasma arc welding (LBW/PAW) 4-42

107 TABLE 4.3 RANKING OF WELDING PROCESSES BY BUMPER MATERIAL WELDING PROCESSES 3, 4 BUMPER MATERIAL 1 MATERIAL STANDARD 2 GMAW FCAW RSW RPW RSeW RPSeW RSeW-HF&1 UW FRW LBW LBW/PAW UNCOATED CQ SAEJ2329 (Grade 1) B B B B B B B b b b b DQSK SAEJ2329 (Grades 2 & 3) B B B B B B B b b b b DQAK SAEJ2329 (Grades 2 & 3) B B B B B B B b b b b 35XLF SAEJ1392 (035XLF) B B B B B B B b b b b 50XLF SAEJ1392 (050XLF) B B B B B B B b b b b 55XLF SAEJ1392 Modified B B B B B B B b b b b 80XLF SAEJ1392 (080XLF) B B B B B B B b b b b 120XF SAEJ2340 (830R) b b B B B B B b b b b 135XF SAEJ2340 Modified b b B B B B B b b b b 140T SAEJ2340 (950DL) b b B B B b B b b b b M190HT SAEJ2340 (1300M) b b b b b b b b b b b 10B21 (Modified) SAEJ403 (10B21 Modified) B B g g b g B b b b b COATED HDG/EG b b g g g g g b b p p 1. Refer to Section and Tables 2.1, 2.2, 2.3, 5.4 and 5.5 for bumper material definitions and properties. 2. See References 4.13, 4.14, 4.15 and Refer to Section for welding process definitions. 4. p = poor g = acceptable b = better B = best 4-43

108 All of the materials in Table 4.3 are commonly used for production bumpers. Examples are given in Tables 5.4 and 5.5 along with a description of each bumper material. In Table 4.3, the welding processes are ranked for the following materials: Hot rolled or cold rolled (uncoated) sheet steel 1. CQ Commercial quality 2. DQSK Drawing quality, special killed de-oxidation practice. 3. DQAK Drawing quality, aluminum killed XLF High-strength low-alloy with sulphide inclusion control, low carbon, 240 MPa (35 ksi) yield strength XLF High-strength low-alloy with sulphide inclusion control, low carbon, 345MPa (50ksi) yield strength XLF High-strength low-alloy with sulphide inclusion control, low carbon, 380MPa(55ksi) yield strength XLF High-strength low-alloy with sulphide inclusion control, low carbon, 550MPa (80ksi) yield strength XF High-strength low-alloy with sulphide inclusion control, low carbon 830MPa (120ksi) yield strength XF High-strength low-alloy with sulphide inclusion control, low carbon 920MPa (135ksi) yield strength T Dual phase structure contains martensite in ferrite matrix, excellent formability prior to strain aging, 965MPa (140ksi) tensile strength. 11. M190HT Martensitic quality, 1310MPa (190ksi) tensile strength B21 Carbon-Boron steel, 1140MPa (165ksi) yield (Modified) strength after hot forming and quenching. hot-dip galvanized or electrogalvanized sheet steel 13. HDG/EG Includes materials one through 12 (above) that have been hot-dip galvanized or electrogalvanized. The ranking of the welding processes for individual materials (one through 12) in the galvanized condition becomes quite complex because of the dual effect of steel grade and metallic coating on weld ability. Thus, one overall ranking is given for each of materials one through 12 in either the hot-dip galvanized or the electrogalvanized condition for each welding process. 4-44

109 The following is an overall explanation of the rankings assigned in Table 4.3: Arc welding (GMAW and FCAW) In general, all steel bumper materials may be arc welded without difficulty. Selection of an appropriate filler metal with proper strength is all that is required. Welding consumable manufacturers can assist with this selection. Consideration should be given to the heat-affected zone in arc welded joints. The graphs in Figure 4.24 are diagrammatic representations of the heat-affected zone for arc welded steel bumper materials. Actual plots are available from steel suppliers and welding consumable manufacturers. Figure 4.24 indicates that as the carbon content in the steel increases, the hardness at the fusion line increases. For example, the carbon content of a martensitic steel depends on its strength level. A higher strength level has a higher carbon content. Figure 4.24 indicates that a martensitic steel with a higher carbon content has increased hardness at the fusion line. Dual phase steel is another example. The carbon content of dual phase steel depends on its production process - as rolled, batch annealed or continuous annealed. All three have different carbon levels and different fusion line hardness. Figure 4.24 also indicates that some steel materials undergo softening and a loss of strength in the heat-affected zone (e.g., microalloy, dual phase, recovery annealed and martensitic materials). Lower heat input during welding helps reduce the degree of softening. Higher strength materials are slightly more difficult to weld than lower strength materials because of the springback associated with higher strength parts. Fixturing, to hold the parts firmly in place during welding, is often required to get defect free welds. Galvanized coatings on steel can cause minor difficulties with arc welding. For example, zinc has a much lower melting and vaporization point than steel. Thus, during welding, zinc fumes are generated. They may be captured by a ventilation system. Also, intermetallic zinc inclusions may be formed during welding. However, inclusions may be minimized by using the FCAW process. The flux scavenges the inclusions and they are removed along with the flux. Resistance welding (RSW, RPW, RSeW and RPSeW) A comparison of resistance spot weldabilty is given in Figure 4.25 for hot rolled, cold rolled and galvanized sheets. Welding lobes are given for representative bumper materials. The lobes are somewhat arbitrary. However, they do allow a rough comparison of the spot weldability of steel materials. For a given material, a welding lobe is expressed as weld time verses weld current at a constant electrode force level. 4-45

110 FIGURE 4.24 HARDNESS IN HEAT-AFFECTED ZONE OF ARC WELDS Hardness Distance From Fusion Line 4-46

111 FIGURE 4.25 RESISTANCE SPOT WELDING COMPARISON a) HOT ROLLED SHEET b) COLD ROLLED SHEET c) GALVANIZED SHEET 4-47

112 Each lobe is a three dimensional diagram. The larger rectangular plane in a lobe represents the base line of weldability. This base line diminishes into the depth of the page to a smaller plane. The reduction in plane size represents sensitivity to some weld parameter such as electrode force. Thus, when the two planes are almost the same size, the material is weldable over a wide range of parameters. On the other hand, if one plane is considerably smaller than the other, weldability losses are expected with a change in parameter. For galvanized sheets, the coating has a marked effect on weldability. To represent the effect of the coating, a square has been placed onto the smaller plane. The lobes in Figure 4.25 are sometimes referred to as operating windows. Weld current and time must be within an operating window to achieve a sound weld. A small operating window means a high degree of control is required in the welding process. Thus, materials with small operating windows are regarded as less weldable than materials with large windows. CQ and DQ hot and cold rolled materials are weldable over a wide range of welding currents and times. Their excellent weldability is often taken as the base against which other materials are compared. CQ and DQ are only minimally affected by electrode force (A high electrode force reduces contact resistance. Thus, either more current or a longer weld time is required). Weld nuggets in CQ and DQ materials are ductile and strong. The hot and cold rolled XLF materials have excellent weldability. They closely match the weldability of CQ and DQ. The XLF materials obtain their strength from microalloying elements (precipitation hardening) and controlled rolling (fine grain size). During welding, loss of precipitation hardening and grain growth may occur, resulting in strength loss in the heataffected zone. Usually, the effect is minimal and does not hinder the application of XLF materials. 120XF and 135XF hot and cold rolled sheets generally obtain their strength through cold work and recovery annealing. While there is no problem welding these materials, a reduction in hardness and strength in the heat-affected zone can occur. Using the lowest current and shortest weld time prevents over welding and improves heat-affected zone strength. Weldability tests on hot and cold rolled dual phase (e.g. 140T) steels show they respond very similar to other steels at their strength level. Martensitic hot or cold rolled sheet (e.g., M190HT) obtains its strength through the quench hardening of somewhat higher carbon steel to martensitic steel. Resistance weld nuggets tend to be brittle and subject to cracking failure. Also, strength loss, through tempering of the base metal, can occur in the heat-affected zone. Regardless, martensitic steels are resistance weldable provided some precautions are taken during welding. 4-48

113 Galvanized coatings add a complexity to welding. In general, as the strength level of the base steel increases, weldability decreases. Also, as strength increases, the required electrode force increases. The effect of the coating on the electrode, plus the higher welding force, cause reduced weldability as indicated by the smaller operating windows for galvanized materials. Coatings also reduce electrode life; thus, the condition of the electrodes must be closely monitored during welding. Frequent dressing or replacement of the electrodes is required. High-frequency welding (RSeW-HF&I) All of the current bumper materials are readily joined by high frequency welding. High frequency welds have only a small heat-affected zone because the welding current is concentrated on the surfaces to be welded. In addition, the squeeze at the point of weld consummation forces any inclusions in the molten weld metal out of the weld zone. Galvanized coatings have little affect on weldability since the heated region of a joint is small. Also, there is little vaporization of the coating and fuming. Upset and friction welding (UW and FRW) Upset and friction welding both result in relatively low heating. Thus, the heat-affect zone not only is small but also contains minimal softening. It is very difficult to align sheet steel parts with these processes. Thus, they are mainly used for bar stock and thicker steel. Laser welding (LBW and LBW/PAW) A laser beam is finely focused and usually associated with higher travel speed, therefore, a laser weld has a very small heat-affected zone due to the higher cooling rate. Thus, any loss of strength in the welded materials, even higher strength ones, is minimal. This process requires excellent fit-up, which is sometimes difficult to achieve during production, especially with higher strength materials due to springback. The vaporization of galvanized coatings can cause a plume, which blocks the laser beam. In such a case, a fume control shielding gas may be used. 4-49

114 5. Design concepts 5.1 Sweep (roll formed sections) and depth of draw (stampings) The current styling trend for vehicles is toward rounded, aerodynamic shapes. This trend has impacted bumper design and challenged bumper manufacturers to provide the highly rounded shapes desired by vehicle stylists. Steel bumper manufacturers have met the challenge and are providing the contours required for both reinforcing beams and facebars. A convenient way of defining the degree of roundness for a stamped or roll formed reinforcing beam is to use the concept of sweep. Sweep expresses the degree of curvature of the outer bumper face, or the face farthest removed from the inside of the vehicle. Sweep is defined in Figure 5.1 and Tables 5.1 and 5.2. Sweep in the camber, X, for a 60 inch (1524 mm) chord length, L, of a given circle of radius, R. Sweep is expressed as the number of one-eighth inches (3.18 mm). For example, if X is 5 inches (127 mm) for an L of 60 inches (1524 mm), the sweep would be 40. Tables 5.1 and 5.2 indicate that a sweep number of 40 corresponds to a radius of curvature of 92.5 inches or 2350 mm. Tables 5.1 and 5.2 also list the cambers for chord lengths smaller than 60 inches (1524 mm). For example, if the camber is inches (68.9 mm) and the chord length is 40 inches (1016 mm), the sweep number is 50. The concept of sweep applies well to a reinforcing beam because it has a near constant radius of curvature and no wrap arounds at the end of the reinforcing beam. Depth of draw is often used to describe the amount of rounding and wrap around on a bumper section, and in particular, a stamped facebar. As shown in Figure 5.2, depth of draw is the distance, X, between the extreme forward point on a bumper and the extreme aft point on a bumper. This distance has a physical significance in that it cannot exceed the opening available with a given stamping press. X is usually stated in inches (millimeters). 5.2 Tailored Products There are two types of tailored products used for bumper beams: laser welded blanks and tailor rolled blanks. A laser welded blank joins two or more flat steel blanks together with laser welding prior to forming. The blanks can have different strengths and thicknesses so that the formed end product has extra thickness and/or strength where it is needed. Examples of laser welded blanks are shown in Figure 5.3. A tailor rolled blank is created by sending a steel coil through a tailor rolling process where the thickness is reduced in certain areas with compressive rollers. The variable thickness coil can then be blanked to create a tailor rolled blank. The tailor rolled blank can then be stamped or hot formed into a component that has extra thickness where it is needed. In the future, it may even be possible to send a tailor rolled coil through a roll forming line to produce roll formed parts with variable thicknesses. Both laser welded blanks and tailor rolled blanks have been implemented into production for bumper beams and are considered a viable method of mass reduction for steel bumper systems. 5-1

115 5-2 FIGURE 5.1 DEFINITION OF SWEEP

116 TABLE 5.1 SWEEP NUMBERS (CAMBER, X, INCHES) SWEEP NO. CHORD LENGTH, L, INCHES RADIUS (inches)

117 TABLE 5.2 SWEEP NUMBERS (CAMBER, X, MILLIMETERS) SWEEP NO. CHORD LENGTH, L, MILLIMETERS RADIUS (mm)

118 5-5 FIGURE 5.2 DEFINITION OF DEPTH OF DRAW

119 5-6 FIGURE 5.3 EXAMPLES OF TAILOR WELDED BLANKS

120 5.3 Latest benckmark bumper beams Examples of recent bumper beams are given in Table 5.3 and Figures 5.4 and 5.5. The examples clearly illustrate that steel bumper beams readily meet the challenges faced by bumper designers -styling, weight, cost and structural integrity. 5-7

121 FIGURE 5.4 ROLL FORMED BEAMS A.) 2012 NISSAN JUKE (REAR) M190 BOX SECTION B.) 2012 HONDA V (FRONT) M190 B-SECTION C.) 2012 LINCOLN NAVIGATOR (FRONT) 120XF BOX SECTION D.) 2013 FORD ESCAPE (REAR) M190 BOX SECTION 5-8

122 FIGURE 5.5 STAMPED FACEBARS E.) 2012 DODGE RAM 1500 (FRONT) 35XLF F.) 2012 TOYOTA TUNDRA (REAR) MILD STEEL 5-9

123 FIGURE 5.6 HOT-FORMED BEAMS G.) 2012 FORD MUSTANG (FRONT) 1500 MPA BORON STEEL BOX SECTION H.) 2012 JAGUAR XF (REAR) 1500 MPA BORON STEEL BOX SECTION I.) 2012 FORD FOCUS (FRONT) 1500 MPA BORON STEEL HAT SECTION WITH FACE PLATE J.) 2012 FORD ESCAPE (FRONT) 1500 MPA BORON STEEL HAT SECTION WITH FACE PLATE 5-10

124 FIGURE 5.7 SHEET HYDROFORMED FACEBAR K.) 2010 FORD RAPTOR (FRONT) MILD STEEL 5-11

125 TABLE 5.3 LATEST BENCHMARK BUMPER BEAMS VEHICLE DESIPTION MASS PRODUCTION LOCATION MATERIAL THICKNESS FEATURES (model year, make, model) METHOD ( or ) (mm) 2012 Nissan Juke 3.3 kg Roll Forming Rear 190T / 1.1 mm Lightweight roll formed bumper with 1300MPa UHSS M Honda V 5.8 kg Roll Forming Front 190T / 1.2 mm Variable radii roll formed UHSS B-section 1300MPa 2010 Ford Raptor Facebar = 9.7 kg Sheet Front Mild Steel 1.6 mm Industry first sheet hydroformed facebar Assembly = 18.7 kg Hydroforming 2012 Dodge Ram kg Stamping Front 035XLF 1.8 mm The EA system is specially designed and tuned to allow multiple bumper modules 2012 Toyota Tundra 25.9 kg Stamping Rear Mild Steel 1.6 mm Full-size, deep-drawn bumper with lightweight bracing 2012 Lincoln Navigator Beam = 2.6 kg Roll Forming Front 120XF 1.7 mm Low cost design with crash compatibility 2012 Ford Mustang 4.5 kg Roll/Hot Front MnB mm 1500 MPa boron steel with closed section, Forming (ACA) aluminized coating, and variable sweep / section 2012 Jaguar XF 5.6 kg Roll/Hot Rear 22MnB5 1.2 mm 1500 MPa boron steel with closed section, Forming (ACA) aluminized coating, and variable sweep / section 2012 Ford Focus (C346) 9.48 kg Hot Stamped Front 10B21MnB 1.8 mm Global design produced in North America, Europe, Russia and China 2013 Ford Escape (C520) kg Hot Stamped Front 10B21MnB 1.7 mm Carry over press parts from C Ford Escape 7.4 kg Roll Forming Rear M190T 1.8 mm Lightweight, ultra high-strength steel bumper solution 5-12

126 TABLE 5.3 (continued) LATEST BENCHMARK BUMPER BEAMS DEFINITIONS XF XLF T MPa MnB High-strength low-alloy (HSLA). Designation number is yield strength in ksi. High-strength low-alloy (HSLA) with low carbon. Formability of this quality is superior to XF quality. Designation number is yield strength in ksi. Martensitic quality. Mega Pascal. Manganese Boron 5-13

127 5.4 Bumper weights, materials and coatings Beams produced by the roll forming production method are shown in Table 5.4, beams produced by the cold stamping method are shown in Table 5.5 and beams produced by the hot forming method are shown in Table 5.6. This data may be used to establish bumper beam benchmarks. In Tables 5.4, 5.5 and 5.6, the bumper beams are grouped by steel grade. The steel grades are defined in the Notes at the end of each table (see also Tables 2.1 and 2.2). For any given steel grade, the bumper beams are listed in decreasing order of steel beam thickness. The vehicle make and model is given for each beam. There are five weight columns in Tables 5.4, 5.5 and 5.6. The first column indicates the weight of the roll formed, cold stamped or hot formed beam itself. For facebars, the weight is that of a painted beam. Chrome facebars are 0.37 kg (1.0 pound) heavier. The second column is the weight of any reinforcements welded to the plain beam. The third column is the combined weight of the plain beam and attached reinforcements. The fourth column tabulates the weight of mounting brackets. The fifth column is the weight of a plain bumper beam, its reinforcements and its mounting brackets. It should be noted that many spaces in the five weight columns are left blank. A blank space indicates that the weight being tabulated is unavailable. The steel products used to manufacture the bumper beams are listed in Tables 5.4, 5.5 and 5.6. Note that both hot rolled (HR) and cold rolled () sheets are delivered in the bare condition. For hot-dip galvanized (HDG) and electrogalvanized (EG) sheets, the coating type and weight are shown. See Section 2.14 for a description of aluminized () sheet. Corrosion protection coatings may be applied by the bumper supplier or by the OEM on the assembly line. The corrosion resistance of a bumper beam depends on all of the coatings applied to it. Thus, the coatings applied by both the bumper supplier and OEM are included in Tables 5.4, 5.5 and 5.6. Sweep or curvature is often imparted to bumper beams during roll forming. For the roll formed beams in Table 5.4, the amount of sweep is shown. A small sweep radius indicates a large amount of curvature to help achieve a high degree of styling. 5-14

128 TABLE 5.4 ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR

129 STEEL THICKNESS GRADE 1 [mm (inches)] 590R 3.20 (0.126) 80XLF 1.60 (0.063) 1.73 (0.068) 3.50 (0.138) 120XF 1.10 (0.043) 1.10 (0.043) 1.14 (0.045) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.067) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Honda Ridgeline WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets Total Chev Jeep Chev Pontiac Saturn Nissan Ford Chrysler Chrylser Chrysler Chrysler Dodge Dodge Dodge Dodge Tahoe Wrangler Tahoe Solstice Sky Sentra P150 Ranger Sebring Sebring Conv Caliber Caliber Charger Charger 7.79 (17.16) 6.20 (13.68) 7.40 (16.32) 5.85 (12.90) 5.85 (12.90) 5.74 (12.65) 2.70 (5.94) 5.71 (12.60) 5.71 (12.60) 6.71 (14.80) 6.75 (14.88) 4.99 (11.00) 6.03 (13.30) 6.71 (14.80) 6.75 (14.88) 1.88 (4.14) 4.58 (10.08) (33.51) 2.44 (5.36) 2.55 (5.61) 2.55 (5.61) 2.9 (6.38) 7.79 (17.16) 6.20 (13.68) (49.83) 5.85 (12.90) 5.85 (12.90) 5.74 (12.65) 7.02 (15.44) 8.26 (18.21) 8.26 (18.21) 6.71 (14.80) 6.75 (14.88) 7.89 (17.36) 6.03 (13.30) 6.71 (14.80) 6.75 (14.88) STEEL PRODUCT HR HR HR 60G60G TABLE 5.4 ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER SWEEP RADIUS mm (inches) (105) (10) 2628 (103) 2628 (103) 2400 (95) 2243 (88) 2350 (93) 2350 (93) 2200 (87) 3348 (132) 2348 (92) 2348 (92) 2200 (87) 3348 (132) 5-15

130 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.30 (0.051) 1.40 (0.055) 1.40 (0.055) STEEL THICKNESS GRADE 1 [mm (inches)] 120XF MAKE MODEL FRONT OR REAR BUMPER Beam Performance Jeep Jeep Jeep Jeep Buick Chev Chev GMC GMC Saturn Saturn Saturn Chev Chev Chev Compass Compass Patriot Patriot Enclave Malibu Impala Acadia Acadia Aura Outlook Outlook Impala Malibu Camaro 4.99 (11.00) 6.03 (13.30) 5.23 (11.53) 6.03 (13.30) 6.56 (14.47) 5.53 (12.19) 6.31 (13.91) 4.63 (10.20) 6.56 (14.47) 5.53 (12.19) 4.63 (10.20) 6.56 (14.47) 6.84 (15.07) 6.19 (13.64) 6.74 (14.85) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 2.17 (4.78) 1.15 (2.25) 2.17 (4.78) 1.15 (2.55) 2.17 (4.78) 8.73 (19.25) 5.78 (12.75) 8.73 (19.25) 5.78 (12.85) 8.73 (19.25) 5.46 (12.04) 6.53 (14.40) 7.11 (15.67) 2.44 (5.39) 2.42 (5.34) 5.81 (12.81) 7.11 (15.67) 2.44 (5.39) 5.81 (12.81) 7.11 (15.67) 0.25 (0.54) 1.20 (2.66) Total (23.04) 6.03 (13.30) (25.93) 6.03 (13.30) (34.92) 7.97 (17.58) 8.73 (19.25) (25.56) (34.92) 7.97 (17.58) (25.66) (34.92) 7.09 (15.61) 7.39 (16.30) 6.74 (14.85) STEEL PRODUCT TABLE 5.4 (continued) ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER SWEEP RADIUS [mm (inches)] (93) 2349 (93) 2349 (93) 2348 (93) 1926 (76) 2743 (108) 2550 (100) 2624 (103) 1925 (76) 2743 (108) 1624 (64) 1926 (76) 2620 (103) 340 (136) 3441 (136) 5-16

131 STEEL THICKNESS GRADE 1 [mm (inches)] 120XF 1.40 (0.055) 1.40 (0.055) 1.50 (0.059) 1.50 (0.059) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.70 (0.067) 1.73 (0.068) 1.80 (0.071) 1.80 (0.071) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Buick Saturn Chev Enclave Aura Corvette 5.49 (12.11) 6.19 (13.64) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 1.15 (2.55) 6.64 (14.66) 5.81 (12.81) 1.20 (2.66) Chev Corvette Chrysler Chrysler Dodge Chev Nissan Subaru Ford Sebring Sebring Conv Challenger Camaro Sentra Tribecca Escape 7.76 (17.11) 7.26 (16.01) 9.77 (21.54) 8.07 (17.79) 7.61 (16.78) 6.29 (13.88) 1.88 (4.14) 9.95 (21.93) 3.87 (8.53) Ford Escape Ford Subaru Mitsubishi Mitsubishi U222 Navigator Tribecca Galant Eclipse 6.92 (15.25) 7.39 (16.29) 6.60 (14.54) 6.60 (14.54) 0.36 (0.79) Total (27.47) 7.39 (16.30) 7.76 (17.11) 7.26 (16.01) 9.77 (21.54) (30.46) 7.61 (16.78) 6.29 (13.88) 7.28 (16.04) 7.39 (16.29) 6.60 (14.54) 6.60 (14.54) STEEL PRODUCT 70G70G EG 70G70G EG 60G60G EG 60G60G EG TABLE 5.4 (continued) ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER SWEEP RADIUS [mm (inches)] (64) 3441 (136) 0 (0) 0 (0) 2061 (81) 2061 (81) 3348 (132) 1689 (67) 2500 (98) 3659 (144) 3310 (130) 1981 (78) 2160 (85) 2710 (107) 3602 (142) 3602 (142) 5-17

132 STEEL THICKNESS GRADE 1 [mm (inches)] 120XF 1.80 (0.071) 1.90 (0.075) 1.90 (0.075) 1.91 (0.075) 140T 1.20 (0.047) 1.40 (0.055) 1.50 (0.059) 1.50 (0.059) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Mitsubishi Ford Lincoln Ford Mitsubishi Eclipse Spyder D258 Taurus Town Car Crown Victoria Endeavor 6.60 (14.54) 6.60 (14.54) (22.58) (22.58) 5.65 (12.45) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 3.66 (8.05) Chev Cobalt Ford MKS Ford Taurus Toyota Mitsubishi Mitsubishi MItsubishi Solara Galant Eclipse Endeavor 6.58 (14.50) 7.34 (16.19) 6.84 (15.08) 6.84 (15.08) 0.11 (0.24) Honda Accord Honda Honda Accord Crossover Accord Total 6.60 (14.54) (25.46) (22.58) (22.58) 5.65 (12.45) 6.69 (14.74) 7.34 (16.19) 6.84 (15.08) 6.84 (15.08) STEEL PRODUCT 60G60G EG 60G60G EG TABLE 5.4 (continued) ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER SWEEP RADIUS [mm (inches)] (142) 2530 (100) 5109 (201) 5109 (201) 3600 (142) (115) 2700 (106) 2700 (106) 2700 (106) 1509 (59) (140) 5-18

133 STEEL THICKNESS GRADE 1 [mm (inches)] 140T 1.80 (0.071) 2.00 (0.079) 2.00 (0.079) 2.00 (0.079) 2.00 (0.079) M190HT 1.10 (0.043) 1.10 (0.043) 1.10 (0.043) 1.10 (0.043) 1.10 (0.043) 1.10 (0.043) 1.14 (0.045) 1.14 (0.045) 1.14 (0.045) 1.14 (0.045) 1.20 (0.047) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Honda Honda Acura Accord Crossover Element MDX 5.73 (12.64) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 1.22 (2.68) 6.95 (15.32) 1.31 (2.88) Acura Honda MDX Crossover Pilot Chev Pontiac Nissan Nissan Nissan Suzuki Ford Lincoln Mercury Suzuki Ford Equinox Torrent Altima Altima Coupe Maxima XL-7 Fusion MKZ Milan XL-7 Taurus 3.81 (8.40) 3.81 (8.40) 4.92 (10.85) 4.92 (10.85) 5.85 (12.90) 3.81 (8.40) 5.74 (12.65) 5.74 (12.65) 5.74 (12.65) 4.00 (8.82) 7.26 (15.97) 1.00 (2.21) 2.58 (5.68) 2.58 (5.68) 0.83 (1.84) 4.81 (10.61) 6.39 (14.08) 6.39 (14.08) 4.83 (10.66) 0.11 (0.24) 0.48 (1.06) Total 8.26 (18.17) 4.81 (10.61) 6.39 (14.08) 4.92 (10.82) 5.03 (11.07) 5.85 (12.90) 6.39 (14.08) 5.74 (12.65) 5.74 (12.65) 5.74 (12.65) 4.83 (10.66) 7.74 (17.03) STEEL PRODUCT 30G30G TABLE 5.4 (continued) ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER SWEEP RADIUS [mm (inches)] (88) (157) 3994 (157) 2500 (98) 2500 (98) 2500 (98) 3994 (157) 2740 (108) 2740 (108) 2740 (108) 4006 (158) 4843 (191) 5-19

134 STEEL THICKNESS GRADE 1 [mm (inches)] M190HT 1.20 (0.047) 1.20 (0.047) 1.30 (0.051) 1.30 (0.051) 1.30 (0.051) 1.33 (0.052) 1.33 (0.052) 1.40 (0.055) 1.40 (0.055) 1.40 (0.055) 1.40 (0.055) 1.40 (0.055) 1.40 (0.055) 1.40 (0.055) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Chev Pontiac Nissan Nissan Nissan Dodge Chrysler Ford Ford Lincoln Lincoln Pontiac Acura Equinox Torrent Altima Altima Maxima Caravan Town & Country Flex Edge MKX MKT G8 MDX 4.79 (10.55) 4.79 (10.55) 6.22 (13.70) 6.22 (13.70) 6.22 (13.70) 8.14 (17.95) 8.14 (17.95) 2.79 (6.15) 5.13 (11.30) 5.13 (11.30) 2.79 (6.15) 5.78 (12.73) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 1.00 (2.21) 0.83 (1.83) 0.31 (0.69) 3.90 (8.59) 3.90 (8.59) 5.79 (12.76) 5.62 (12.38) 6.53 (14.39) 6.69 (14.74) 6.69 (14.74) 3.59 (7.92) 3.59 (7.92) 3.59 (7.92) 1.22 (2.68) Honda Odyssey Total 5.79 (12.76) 5.62 (12.38) 9.81 (21.62) 9.81 (21.62) (22.31) 8.14 (17.95) 8.14 (17.95) 6.69 (14.74) 6.35 (13.98) 5.13 (11.30) 6.69 (14.74) 5.78 (12.73) STEEL PRODUCT TABLE 5.4 (continued) ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER SWEEP RADIUS [mm (inches)] (158) 4006 (158) 4000 (158) 4000 (158) 4000 (158) 2543 (100) 2543 (100) 2325 (92) 3500 (138) 3500 (138) 2325 (92) 7934 (312) 5-20

135 STEEL THICKNESS GRADE 1 [mm (inches)] M190HT 1.54 (0.061) 1.54 (0.061) 1.54 (0.061) 1.54 (0.061) 1.50 (0.059) 1.50 (0.059) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.80 (0.071) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Chrysler Dodge Honda Honda Ford Lincoln Town & Country Caravan -V -V Crown Victoria Town Car 7.72 (17.02) 7.72 (17.02) 3.34 (7.36) 3.41 (7.52) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 0.94 (2.07) 2.29 (5.06) 4.28 (9.43) 5.70 (12.58) 3.23 (7.12) 3.23 (7.12) 1.09 (2.41) 1.77 (16.49) Ford Lincoln Lincoln Mercury Chev Fusion MKZ MKT Milan Cobalt 4.42 (9.74) 4.42 (9.74) 5.49 (12.11) 4.42 (9.74) 0.54 (1.18) Chev HHR Chev HHR Ford Explorer Honda Ridgeline 5.40 (11.90) 4.69 (10.34) Total (24.14) (24.14) 5.37 (11.84) 7.47 (16.49) 4.42 (9.74) 4.42 (9.74) 6.03 (13.29) 4.42 (9.74) (22.24) STEEL PRODUCT TABLE 5.4 (continued) ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER SWEEP RADIUS [mm (inches)] (85) 2148 (85) 2500 (98) 3400 (134) 3096 (122) 3096 (122) 3403 (134) 3403 (134) 5000 (197) 3403 (134) (78) 2181 (86) 5-21

136 TABLE 5.4 (continued) ROLL FORMED BUMPER BEAMS 2009 MODEL YEAR STEEL THICKNESS GRADE 1 [mm (inches)] M190HT M220HT 1.80 (0.071) 1.45 (0.057) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Honda Cadillac Odyssey CTS WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets Total STEEL PRODUCT BUMPER SUPPLIER COATING ASSEMBLY LINE COATING SWEEP NUMBER 43 SWEEP RADIUS [mm (inches)] 2181 (86) 1.45 (0.057) Cadillac CTS 1.70 (0.067) Ford MKS 6.76 (14.88) 1.12 (2.46) 7.88 (17.34) 1.06 (2.34) 8.94 (19.68) 60G60G (86) NOTES: 1. A blank cell means that data is unavailable for that cell. 2. A zero (0) sweep number means the beam is straight/flat. 3. Sweep numbers are rounded to the nearest whole number. Sweep radii are actual radii. DEFINITIONS: 590R Ferrite-bainite transformation strengthening grade. Minimum tensile strength is 590 MPa. XF Recovery annealed quality. Strength is achieved primarily through cold work during cold rolling at the steel mill. Designation number (e.g. 50) is minimum yield strength in ksi. XLF Microalloy quality. Strength is obtained through small quantities of alloying elements such as vanadium and niobium. Designation number (e.g. 120) is minimum yield strength in ksi. T Dual phase quality. Structure contains martensite in ferrite matrix. Designation number (e.g. 140) is minimum tensile strength in ksi. M..HT Martensitic quality. Strength is determined by carbon content. Designation number (e.g. 190) is minimum tensile strength in ksi. Cold rolled sheet. HR Hot rolled sheet. EG Electrogalvanized sheet. The six-character descriptor designates coating type and weight. Two numeric characters (e.g. 60) denote coating weight in g/m 2. An alphabetic character denotes coating type. The first three characters denote coating weight and type on one side of the sheet and the last three characters denote coating weight and type on the opposite side of the sheet. G Hot-dip galvanized sheet. The six-character descriptor designates coating type and weight. Two numeric characters (e.g. 90) denote coating weight in g/m 2. An alphabetic character denotes coating type. The first three characters denote coating weight and type on one side of the sheet and the last three characters denote coating weight and type on the opposite side of the sheet. 5-22

137 TABLE 5.5 STAMPED FACEBARS 2009 MODEL YEAR

138 STEEL THICKNESS GRADE 1 [mm (inches)] 1008/ (0.055) 1.60 (0.063) 1.60 (0.063) 1.60 (0.063) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.90 (0.071) 2.00 (0.079) 2.00 (0.079) 2.00 (0.079) 2.01 (0.079) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Toyota Toyota Toyota Nissan Dodge Mitsubishi Nissan Nissan Nissan Nissan GM Tundra Tundra Tacoma Frontier Dakota Raider Frontier Titan Xterra Titan Hummer (23.33) (22.65) 8.53 (18.80) 9.11 (20.08) 9.66 (21.30) 9.66 (21.30) 8.26 (18.20) (32.08) 6.94 (15.30) (24.09) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets Ford Mazda Ford Ranger B-series Econoline (Step) 7.12 (15.7) 7.12 (15.7) (29.6) 4.17 (10.4) 4.17 (10.4) 5.42 (11.95) (26.1) (26.1) (41.55) 6.35 (14.0) Total (23.33) (22.65) 8.53 (18.80) 9.11 (20.08) 9.66 (21.30) 9.66 (21.30) 8.26 (18.20) (32.08) 6.94 (15.30) (24.09) (26.1) (26.1) (55.5) STEEL PRODUCT TABLE 5.5 STAMPED FACEBARS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - paint back side - side - chrome or paint back side - paint side - chrome or paint back side - paint side - chrome or paint back side - paint 5-23

139 STEEL THICKNESS GRADE 1 [mm (inches)] 1008/ (0.090) 2.29 (0.090) 2.29 (0.090) 2.29 (0.090) 2.30 (0.090) 2.50 (0.098) DR (0.071) 1.80 (0.071) 1.80 (0.071) BH (0.063) 35SLK 1.90 (0.075) 1.90 (0.075) 35XLF 1.64 (0.065) 1.80 (0.071) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Chev Chev Chev GMC Ford GM Tahoe Suburban Silverado Sierra 400 Econoline Hummer (46.71) (46.71) (46.71) (46.71) (29.0) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets (29.0) 1.77 (3.9) Ford Ford Ford Chev Super Duty Super Duty Econoline Silverado (37.59) 8.44 (18.60) (31.81) GMC Chev Dodge Dodge Canyon Colorado Ram 1500 Ram HD (44.60) (44.60) 9.54 (20.99) (29.29) (29.29) 9.55 (21.06) Total (46.71) (46.71) (46.71) (46.71) (32.9) (37.59) 8.44 (18.60) (31.81) (44.60) (44.60) 9.54 (20.99) (50.35) HR HR HR HR STEEL PRODUCT TABLE 5.5 (continued) STAMPED FACEBARS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] side - chrome or paint back side - side - chrome back side - side - chrome or paint back side - side - chrome or paint back side - side - chrome or paint back side - paint 135 (5.3) 135 (5.3) 135 (5.3) 135 (5.3) side - paint back side - side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - acrylic compound side - chrome or paint back side - acrylic compound side - chrome or paint back side - acrylic compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - paint 165 (6.5) 165 (6.5) 92 (3.6) 5-24

140 STEEL THICKNESS GRADE 1 [mm (inches)] 35XLF 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.91 (0.075) 1.91 (0.075) 1.91 (0.075) 2.01 (0.079) 2.01 (0.079) 50XLF 1.80 (0.071) 1.91 (0.075) 1.91 (0.075) 1.91 (0.075) 2.00 (0.079) 2.00 (0.079) 2.00 (0.079) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Chev GMC Dodge Dodge Chev Silverado Sierra Ram 1500 Ram HD Colorado 7.42 (16.35) 7.42 (16.35) (30.66) (33.71) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets Mazda Ford Chev GMC Dodge Ford Ford Ford GMC Chev GMC B Series Pickup Ranger Express 600 Savana 600 Ram 2DR F-150 F-150 Styleside (5000 lb. tow) F-150 Styleside (10500 lb. tow) Sierra Express Savana 7.26 (16.00) 7.26 (16.00) (24.12) (24.12) (38.00) (29.8) 6.44 (14.2) 6.44 (14.2) 9.61 (21.18) (35.96) (35.96) 3.57 (7.86) 3.57 (7.86) 1.97 (4.36) 8.97 (19.79) 9.90 (21.83) (23.86) (23.86) (34.16) (33.99) (36.03) 1.19 (2.62) 1.19 (2.62) 6.38 (14.07) 6.38 (14.07) 5.67 (12.50) 5.8 (12.8) 4.55 (10.04) 5.87 (12.96) Total 7.42 (16.35) 7.42 (16.35) (30.66) (33.71) (26.48) (26.48) (38.2) (38.2) (50.5) (59.60) (44.03) (48.99) 9.61 (21.18) (35.96) (35.96) HR HR STEEL PRODUCT TABLE 5.5 (continued) STAMPED FACEBARS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - acrylic compound side - chrome or paint back side - paint side - chrome or paint back side - paint or side - chrome or paint back side - side - chrome or paint back side - side - chrome or paint back side - acrylic compound side - chrome or paint back side - paint side - chrome or paint back side - paint side - chrome or paint back side - paint side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound 140 (5.5) 117 (4.6) 117 (4.6) 132 (5.2) 132 (5.2) 191 (7.5) 140 (5.5) 160 (6.3) 160 (6.3) 5-25

141 TABLE 5.5 (continued) STAMPED FACEBARS 2009 MODEL YEAR STEEL THICKNESS GRADE 1 [mm (inches)] 50XLF 55XLF 80XLF 2.00 (0.079) 2.00 (0.079) 2.00 (0.079) 2.26 (0.089) 2.26 (0.089) 2.26 (0.089) 2.26 (0.089) 2.26 (0.089) 2.26 (0.089) 1.32 (0.050) MAKE MODEL FRONT OR REAR BUMPER Beam Performance Dodge Dodge Dodge Chev Chev Chev GMC Chev GMC Honda Ram Ram 1500 Ram HD Suburban Suburban 430 Tahoe Yukon Silverado Sierra HD Element (29.29) (30.66) (33.71) (33.71) (31.50) (31.50) (31.50) (31.50) (31.50) (31.50) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets (29.29) 9.55 (21.06) Total (50.35) (30.66) (33.71) (33.71) (31.50) (31.50) (31.50) (31.50) (31.50) (31.50) HR HR HR HR HR HR STEEL PRODUCT BUMPER SUPPLIER COATING side - chrome or paint back side - thermoplastics, water based compound side - chrome or paint back side - paint side - chrome or paint back side - thermplastics, water based compound side - chrome or paint back side - thermoplastics, water based compound side - chrome back side - side - chrome back side - side - chrome or paint back side - side - chrome or paint back side - side - chrome or paint back side - side - chrome or paint back side - ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] 127 (5.0) 127 (5.0) 127 (5.0) 127 (5.0) 127 (5.0) 127 (5.0) NOTES: 1. A blank cell means that data are unavailable for that cell. 2. Beam weight is for a painted beam. Add 0.37 kg (1.0 pound) for a chrome beam. DEFINITIONS 1008/1010 Low carbon quality. Mechanical properties are not certified. DR210 Dent resistant quality. Minimum yield strength of 210MPa (30 ksi) as-shipped from the steel mill. Strength increases due to work hardening during forming. BH 210 Bake hardenable quality. Minimum yield strength of steel is 210 MPa (30 ksi) as-shipped from the steel mill. Strength increases due to work hardening during forming and baking during coating. SLK Structural quality. Killed, fine grain practice. Designation numbr (e.g. 35) is minimum yield strength in ksi. XLF Microalloy quality. Strength is obtained through small additions of alloying elements such as vanadium and niobium. Designation number (e.g. 50) is minimum yield strength in ksi. Cold rolled sheet. HR Hot rolled sheet. 5-26

142 TABLE 5.6 HOT FORMED BUMPER BEAMS 2009 MODEL YEAR

143 6.00 (13.23) 7.20 (15.87) 8.00 (17.64) 5.00 (11.03) 5.00 (11.03) 5.00 (11.03) 4.00 (8.82) 4.00 (8.82) 6.00 (13.23) 11.6 (25.52) STEEL THICKNESS GRADE 1 [mm (inches)] 10B21(M) 4.0 (0.157) 3.50 (0.138) 3.00 (0.118) 2.75 (0.108) 2.70 (0.108) 2.70 (0.106) 2.50 (0.098) 2.50 (0.098) 2.50 (0.098) 2.50 (0.098) 2.35 (0.093) 2.14 (0.084) 2.14 (0.084) MAKE MODEL FRONT OR REAR BUMPER Beam Performance BMW 6 Series WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets Total VW VW SEAT A4 Jetta USA C1 USA New Beetle Ibiza 6.00 (13.23) VW VW VW VW Seat VW VW VW VW B5 USA Passat B5 USA Passat PQ24 Brazil New Polo PQ24 A04 New Polo PQ24 S04 New Ibiza Tiguan Scirocco Golf Jetta 6.50 (14.33) 8.00 (17.64) 2.00 (4.41) 2.80 (6.17) 2.80 (6.17) 4.00 (8.82) 4.20 (9.26) 3.50 (7.72) 6.00 (13.23) 3.1 (6.82) 0.70 (1.54) 3.00 (6.61) 2.20 (4.85) 2.20 (4.85) 2.50 (5.51) HR HR HR HR HR HR HR HR HR STEEL PRODUCT TABLE 5.6 HOT FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] 65 (2.6) 80 (3.1) 82 (3.2) 105 (4.1) 70 (2.8) 70 (2.8) 70 (2.8) yes 50 (2.0) yes 60 (2.4) 65 (2.6) 65 (2.6) 5-27

144 STEEL THICKNESS GRADE 1 [mm (inches)] 10B (0.084) 2.00 (0.079) 2.00 (0.079) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.80 (0.071) 1.75 (0.069) 1.60 (0.063) MAKE MODEL FRONT OR REAR BUMPER Beam Performance VW/ Skoda Opel Smart VW Saab Saab VW- China VW- Seat VW VW VW T5 New 307 Zafira Pure Coupe SE241 New Cordoba 602 New New 9-3 X4 (X41, X42) New Xantia W456 Brasil former (SUV) C1 USA New Beetle C1 ECE New Beetle D1 (Phaeton) 3.30 (7.28) 4.30 (9.48) 4.09 (9.02) 2.00 (4.41) 2.80 (6.17) 2.80 (6.17) 2.80 (6.17) 2.80 (6.17) 3.60 (7.94) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 1.80 (3.97) 0.50 (1.10) 3.13 (11.62) 3.00 (6.61) 2.20 (4.85) 2.20 (4.85) 2.20 (4.85) 3.20 (7.05) 6.60 (14.55) Total 5.10 (11.24) 4.80 (10.58) 7.22 (15.92) 5.00 (11.03) 5.00 (11.03) 5.00 (11.03) 5.00 (11.03) 6.00 (13.23) 4.97 (10.96) (22.49) HR HR HR HR HR HR HR HR HR STEEL PRODUCT TABLE 5.6 (continued) HOT FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] 85 (3.3) Zinc coated 40 (1.6) 60 (2.4) 60 (2.4) yes 60 (2.4) yes 60 (2.4) 75 (3.0) raw/cb-zinc yes 85 (3.3) 5-28

145 STEEL THICKNESS GRADE 1 [mm (inches)] 10B (0.059) 1.50 (0.059) 1.50 (0.059) 1.50 (0.059) 1.25 (0.049) 1.20 (0.047) 1.20 (0.047) 1.20 (0.047) 1.20 (0/047) MAKE MODEL FRONT OR REAR BUMPER Beam Performance VW Ford BMW W456 Brasil former (SUV) Mondeo 5 Series 2.10 (4.63) 2.85 (6.28) WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets 7.20 (15.88) Chrysler A-Class VW Polo A05 Toyota Toyota Ford Auris Verso Mustang 1.82 (4.01) 1.8 (3.96) 2.0 (4.4) 2.0 (4.4) Ford Mustang VW BMW D1 (Phaeton) 3 Series 4.15 (9.15) 3.00 (6.61) BMW MINI BMW MINI BMW BMW MINI Countryman X5 Total (22.16) (22.77) 3.6 (7.92) 5.47 (11.90) 3.12 (6.88) 3.82 (8.41) 3.80 (8.36) 4.3 (9.46) 4.2 (9.24) 7.15 (15.76) 4.95 (10.91) 5.5 (12.13) 6.1 (13.42) 8.9 (19.58) 8.1 (17.82) HR HR HR HR STEEL PRODUCT TABLE 5.6 (continued) HOT FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] Zinc coated yes 27 (1.1) 80 (3.1) 80 (3.1) 70 (2.8) 5-29

146 STEEL THICKNESS GRADE 1 [mm (inches)] 10B21 1.8mm 2.0mm MAKE MODEL FRONT OR REAR BUMPER Beam Performance BMW X5 WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets Chrysler E-class Ford Fiesta Ford Fiesta Ford Focus C-Max Ford Focus C-Max Ford S-Max/Galaxy Ford S-Max/Galaxy Ford Mondero PSA Peugeot 3-7 Saab 9-3 Saab 9-3 Convert Saab 9-5 SEAT Ibiza SEAT Leon SEAT Leon Total 5.5 (12.1) 8.93 (19.69) 8.6 (18.92) 3.3 (7.26) 10.0 (22.0) 4.53 (10.0) 10.0 (22.05) 5.00 (11.03) 5.00 (11.03) 10.4 (22.88) 5.00 (11.03) 6.00 (13.23) 4.97 (10.96) (22.49) (22.49) 7.,27 (16.03) STEEL PRODUCT TABLE 5.6 (continued) HOT FORMED BUMPER BEAMS 2009 MODEL YEAR BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] 5-30

147 TABLE 5.6 (continued) HOT FORMED BUMPER BEAMS 2009 MODEL YEAR STEEL THICKNESS GRADE 1 [mm (inches)] 10B21 MAKE MODEL FRONT OR REAR BUMPER Beam Performance SEAT Altea WEIGHT [kg (pounds)] Reinforcements Subtotal Mounting Brackets Total STEEL PRODUCT BUMPER SUPPLIER COATING ASSEMBLY LINE COATING DEPTH OF DRAW [mm (inches)] SEAT Altea AUDI A3 VOLVO VOLVO MERCEDES VW VW Mazda Mazda VW XC60 S60 GL SLW Caddy Touran Mazda 6 Mazda 6 Russland 5.1 (11.22) 6.0 (13.2) 5.68 (12.5) 3.84 (8.4) 7.1 (15.62) 2.6 (5.72) 5.4 (11.88) FIAT FIAT FIAT 500 FIAT (9.9) 3.9 (8.58) NOTES: 1. A blank cell means that data are unavailable for that cell. DEFINITIONS 10B21 Carbon-Boron quality (SAE 10B21 modified). Beams are hot formed. After quenching, the yield strength is about 1140 MPa (165ksi). 5-31

148 5.5 Current steel bumper design - passenger cars A flow chart for designing passenger car bumpers is shown in Figure 5.8. There are two paths. One path is for vehicles sold only in North America and the other path is for vehicles sold in both North America and Europe. Two types of standards influence bumper design: mandatory government standards and voluntary insurance industry standards. In the United States, the federal standard regulating bumper design is referred to as the National Highway Traffic Safety Administration standard (see Section 6.1). The federal standard that regulates bumper design in Canada (see Section 6.2) allows the use of the NHTSA standard. Thus, the NHTSA standard covers vehicles to be sold in both Canada and the United States. In Europe, the Economic Commissions for Europe standard (see Section 6.3), which is similar to the NHTSA standard, regulates bumper design. In addition, bumpers must conform to Pedestrian Protection regulations (see Section 5.8). The Insurance Institute for Highway Safety (IIHS) in an effort to reduce the cost of passenger vehicle bumper repairs, has developed a test standard that simulates a broader range of impacts occurring in actual on-the-road crashes (see Section 6.4). The voluntary IIHS tests are more severe than the NHTSA tests. The IIHS standard provides a weighted damage estimate that is used when determining overall rating for a vehicle to be sold in North America. This target is used when designing the vehicle s bumpers. Similar to IIHS, the European insurance industry publishes two voluntary tests to prevent unnecessary damage in low speed crashes. These tests are referred to as the RCAR Structural Test (see Section 6.6) and the RCAR Bumper Test (see Section 6.7) Typical bumper design - North American passenger cars In Figure 5.8, the designer s first step is to determine the OEM Internal design requirements. For example, are the IIHS tests to be included in the design process? Are there OEM requirements, such as packaging, that are not included in the flow chart? If the answer to the latter question is yes, the designer must modify the flow chart. If there are no IIHS requirements, the designer moves directly to a NHTSA Base Design. Thus, it is suggested the corner impact be used to establish the base design. The designer then moves on to the longitudinal pendulum and barrier impacts. If the NHTSA damage and A+B planes force criteria have been satisfied, a final design has been reached. If the OEM has specified IIHS requirements, it is suggested the designer start by satisfying the OEM IIHS requirements. Usually, these requirements are more demanding than the NHTSA criteria, especially if the IIHS target is a zero or minimal damage estimate. 5-32

149 The designer may be designing a bumper, a bumper or both bumpers. If only a or bumper is being designed, the designer must establish the IIHS damage estimate desired by the OEM for the bumper. If both a and bumper are being designed, the designer must establish the desired IIHS weighted damage estimate. In the flow chart, the only difference between the or and the and paths is the acceptance criterion. The criterion for a single bumper is the damage estimate for that bumper. The criterion if both bumpers are being designed is the weighted damage estimate, which is calculated using the damage estimate for each of the two bumpers. Once an acceptable IIHS design has been achieved, the designer verifies that the NHTSA criteria have been met before reaching a final design Typical bumper design - North American and Europe passenger cars In Figure 5.8, the designer s first step is to determine the OEM internal design requirements. For example, are the IIHS and RCAR tests to be included in the design process? Are there OEM requirements, such as packaging, that are not included in the flow chart? If the answer to the latter question is yes, the designer must modify the flow chart. In general, the NHTSA and ECE requirements are similar as are the IIHS and RCAR Bumper Test Requirements. However, the requirements associated with the RCAR Structural Test are more demanding than the NHTSA, ECE and RCAR Bumper Test requirements. For this reason, plus the fact a European bumper must have pedestrian protection, the flow chart goes through the European path before the North American path. A European bumper must meet Pedestrian Protection requirements. Thus, a design concept that will provide the required Pedestrian Protection must be selected and it is logical to commence the design process here for a bumper. After preparing a Base Design that satisfies Pedestrian Protection requirements, and if there are no RCAR requirements, the designer addresses the ECE requirements. Often, the pendulum corner impact is the most demanding ECE case. Thus, it is suggested the corner impact be used first to verify the Base Design. After the designer has satisfied the ECE requirements, the designer would proceed through the North American bumper path as outlined in Section to reach a Final Design. For a bumper, if RCAR requirements are to be met, it is suggested the RCAR requirements be addressed before the ECE requirements because the RCAR requirements are more demanding. The RCAR Structural Test is more demanding than the RCAR Bumper Test. Thus, if the RCAR Structural Test is a requirement, it should be addressed before the RCAR Bumper Test. Once a design that is acceptable from the RCAR point of view has been achieved, the designer moves through the ECE requirements and then the North American bumper path as outlined in Section to reach a Final Design. 5-33

150 A bumper would essentially follow the same path as a bumper. However, one major difference is that Pedestrian Protection is not a requirement and this step in the design process is bypassed. 5.6 Current steel bumper design - pickups, full size vans and sport utilities There are no federal regulations in the United States or Canada for bumpers on pickups, full size vans or SUVs. These bumpers are designed to meet OEM internal specifications. Thus, a designer should develop a design flow chart using Figure 5.8 as a model. 5-34

151 NO DETERMINE OEM INTERNAL DESIGN REQUIREMENTS N. AMERICA OR N. AMERICA & EUROPE YES IIHS REQUIREMENTS? N.A. NO FRONT OR REAR OR FRONT & REAR FRONT OR REAR FRONT & REAR ESTABLISH DESIRED IIHS DAMAGE ESTIMATE ESTABLISH DESIRED IIHS WEIGHTED DAMAGE ESTIMATE FRONT OR REAR BASE DESIGN IIHS 10km/h OVERLAP IIHS 5km/h CORNER FRONT BASE DESIGN IIHS 10km/h OVERLAP IIHS 5km/h CORNER ACCEPTABLE DAMAGE ESTIMATE? REAR BASE DESIGN IIHS 10km/h OVERLAP IIHS 5km/h CORNER YES N.A. & EUROPE FRONT OR REAR REAR YES YES ACCEPTABLE WEIGHTED DAMAGE ESTIMATE? NO PEDESTRIAN PROTECTION BASE DESIGN NHTSA BASE DESIGN PENDULUM 2.5 mph LONG 1.5 mph CORNER BARRIER 2.5 mph NON-BUMPER VISUAL OR SAFETY 8 FUNCTIONAL ITEM DAMAGE? NO 2000 lbs. < A + B PLANES FORCE? NO NO ACCEPTABLE YES RCAR REQUIREMENTS? NO YES ESTABLISH DESIRED DAMAGEABILITY & REPAIRABILITY REQUIREMENTS BASE DESIGN STRUCTURAL TEST 15 km/h FRONT 15 km/h REAR BUMPER TEST 10 km/h FRONT 10km/h REAR ACCEPTABLE NO DAMAGEABILITY YES & REPAIRABILITY REQUIREMENTS? FINAL DESIGN FIGURE TYPICAL BUMPER DESIGN FOR PASSENGER CARS AND MINIVANS ECE BASE DESIGN 2.5 mph LONG 1.5 mph CORNER YES NON-BUMPER SAFETY & FUNCTIONAL DAMAGE? NO

152 5.7 Auto/Steel Partnership high speed bumper design - North American passenger cars The Auto/Steel Partnership (A/SP) commissioned Quantech Global Services to conduct a study on the -end of a four-door, mid-size sedan. The objective was to reduce the cost and mass of the end structure through the use of advanced high-strength steels. The study included the development of a high speed bumper system. Current North American passenger cars have low speed bumper systems. Thus, Quantech s first task for the high speed bumper system was to establish design criteria and a design process. Sections and outline the results of Quantech s research into these two areas Quantech design criteria for high speed steel bumper system Quantech, in consultation with A/SP, established the design criteria for a high speed bumper system as: 1. No bumper damage or yielding after a 5mph (8km/h) al impact into a flat, rigid barrier. Note: This criterion does not apply to low speed bumpers, where controlled yielding and deformation are beneficial. 2. No intrusion by the bumper system ward of the engine compartment rails for all impact speeds less than 9mph (15km/h). 3. Minimize the lateral loads during impacts in order to reduce the possibility of lateral buckling of the rails. 4. Full collapse of the system during Danner (RCAR), NCAP, and IIHS high speed crash without inducing buckling of the rails. 5. Absorb 1% of the total energy every millisecond. 6. Absorb 15% of the total energy in the NCAP crash, including engine hit. 7. Use the -end crush space efficiently. 8. Meet the air bag sensor requirements in low, medium and high speed impacts. 9. No detrimental affect on baseline body-in-white static or dynamic stiffness. Bumpers should protect car bodies from damage in low speed collisions - the kind that frequently occurs in congested urban traffic. The IIHS Low Speed Crash Test Protocol (see Section 6.4) addresses this issue. For marketing reasons, many current bumper systems are designed to ensure no or minimal cost of repair after the IIHS 5mph (8km/h) barrier impact. A/SP believes all future vehicles should meet this requirement. Thus, Criterion 1 was set to achieve zero damage and no or minimal cost of repair after the IIHS 5mph (8km/h) barrier impact. Criterion 4 addresses three high speed load cases: 1. 40%-9mph Danner (RCAR Test - see Section 6.6 and Reference 6.10). This load is a 9mph (15km/h) impact at a 40% offset into a rigid barrier. The A/SP objective is to have no damage to the radiator and other costly equipment in the -end and to have no damage to the rail beyond 300mm (12inches). 5-36

153 5.7.2 Flow Chart for high speed system mph NCAP (NHTSA New Car Assessment Program, Reference 5.2). This load is a 35mph (56km/h) impact into a rigid barrier. The A/SP objective is to maximize the energy absorbed in the bumper system %-40mph IIHS (Reference 5.3). This load case is a 40mph (64km/h) impact at a 40% offset into a deformable barrier. The A/SP objective is to ensure the bumper system does not break and is capable of transferring the load to the right rail, thereby minimizing the damage. A major objective of A/SP is to reduce vehicle weight using steel as the material of choice. Criterion 6 addresses this objective. Traditional bumper systems absorb about 8-11% of the energy in the 35mph (56km/h) NCAP crash. If bumper systems were to dissipate higher levels, there would be an opportunity for mass savings in the end structure. To capitalize on this opportunity, A/SP set 15% energy absorption as a stretch goal for future bumper systems. For the reason of low cost with lightweight, steel is the material of choice for future, as well as current, bumper beams. The flow chart in Figure 5.8 outlines the design process developed by Quantech for a high speed bumper system having a steel beam. The process is a logical route to satisfying the design criteria outlined in Section First, a base design is prepared. It is checked against the IIHS low speed [5mph (8km/h)] flat al barrier load case. If there is damage or yielding, the base design is modified. If not, the three high speed load cases are analyzed in the following sequence: 1. 40% offset - 9mph (15km/h) Danner mph (56km/h) NCAP % offset - 40mph (64km/h) IIHS. The results from the analyses of the three high speed load cases are compared to the design criteria in Section If all of the criteria are met, the designer assesses the amount of energy absorption. Energy absorption should be maximized because the higher the amount, the greater the opportunity to reduce mass in the end structure. If the designer believes energy absorption has been maximized, a viable design has been captured. If not, the learning from the three high speed load cases is used to improve the base design and reach a viable design. Usually, three or four viable design alternatives are developed using the above process. The designer then selects one of the alternatives as the Preferred Design. The Preferred Design should be lightweight and easy to manufacture. Also, it should be easy to assemble and integrate with the rails. Cost is also a consideration when selecting the Preferred Design. 5-37

154 FIGURE 5.9 AUTO/STEEL PARTNERSHIP BUMPER DESIGN FOR HIGH SPEED SYSTEM NORTH AMERICAN PASSENGER CARS AIR BAG SENSOR REQUIREMENTS BASE DESIGN AIR BAG G LOW SPEED 5 mph DANNER 40% OFFSET 15 km/h (9 mph) HIGH SPEED 35 mph (NCAP) 40%-40 mph (IIHS) NO ACCEPTABLE? NO/MINIMUM DAMAGEABILITY OF RAIL ENERGY ABSORPTION MAXIMIZED? YES CAPTURE A VIABLE DESIGN YES NO USE LEARNING FOR AN IMPROVED DESIGN PREFERRED DESIGN Source: Auto/Steel Partnership and Quantech Global Services 5-38

155 5.8 Bumper design for pedestrian impact Pedestrian safety is a globally recognized safety concern. Efforts towards modifying vehicle designs to offer some protection for pedestrians began in earnest in the 1970s. At the same time, test procedures to evaluate the performance of new designs developed. Pedestrian safety has improved significantly since then. The Steel Market Development Institute wished to learn how pedestrian safety might affect steel bumper systems. Thus, it retained Dr. Peter Schuster, California Polytechnic State University, to study this topic. The following information is based on his work (Reference 5.4) Impact tests The European Union has been subjecting select vehicles to a battery of tests (al, side and pedestrian) as part of its new car assessment program (EuroNCAP, Reference 5.5). The EuroNCAP pedestrian tests (Figure 5.9) consist of: leg to bumper impacts with a leg-form impactor, upper leg to hood edge impacts with an upper leg-form impactor, head to hood top impacts with two different head-form impactors. The European Union typically subjects a vehicle to three leg to bumper impacts, three upper leg to hood edge impacts and up to 18 head to hood top impacts. The results are reported with a four-star rating system, similar to that used in the United States NCAP program. Japan s NCAP program includes tests that simulate pedestrian head to hood top impacts. However, leg to bumper and upper leg to hood edge impacts are not included. Currently, North American NCAP programs do not include pedestrian requirements. However, the high number of pedestrian accidents in North America and the trend to global vehicle design, likely mean that pedestrian impact requirements will come to North America in the longer term EuroNCAP leg to bumper impacts with a leg-form impactor This test significantly influences bumper design. Thus, a brief discussion of the requirements is in order. First, it should be stated that the purpose of this test is to reduce severe lower limb injuries in pedestrian accidents. The most common lower limb injuries are intra-articular bone fractures, ligament ruptures and comminuted fractures. In this test, a leg-form impactor is propelled toward a stationary vehicle at a velocity of 40 km/h (25 mph) parallel to the vehicle s longitudinal axis. The test can be performed at any location across the face of the vehicle, between the 30 bumper corners. 5-39

156 5.8.3 Government regulations The leg-form impactor is shown in Figure It consists of two semi-rigid 70mm (27.6 inches) diameter core cylinders (the tibia and femur ) connected by a deformable knee joint. This core structure is wrapped in 25mm (1 inch) of foam flesh covered by 6mm (0.24 inches) of neoprene skin. The performance criteria proposed for 2010 are shown in Figure The maximum acceleration of the tibia is intended to prevent fracture of the tibia due to bumper contact. The maximum knee bend angle and shear deformation are intended to prevent severe knee joint injuries such as ligament ruptures and intra-articular bone fractures. As of June 2005, there were no government regulations for pedestrian impact. However, the European Union and major vehicle associations have negotiated an agreement (Reference 5.6). The agreement states that new vehicles will achieve a limited level of pedestrian impact performance starting in 2005, with an increased performance in The limits shown in Figures 5.9 and 5.11 are the targets for For 2005, the leg to bumper targets are: knee bending < 20 knee shear < 6mm (0.24 inches) acceleration < 200g Design approaches There are two general approaches to designing a bumper system for pedestrian safety: Provide end vehicle components to cushion the impact and support the lower limb Provide sensors and external airbags to cushion the impact and support the lower limb Cushioning the impact Cushioning reduces the severity of bone fractures. It is directly related to the acceleration impact criterion shown in Figure Limiting the lower limb acceleration to 150g requires a bumper stiffness lower than that usually provided to satisfy the damageability criteria associated with low-speed [8 km/h (5 mph)] vehicle impact. Thus, a pedestrian friendly bumper system must be capable of limiting leg-form acceleration without sacrificing vehicle damageability in a low-speed impact Supporting the lower limb Supporting the lower limb reduces the risk of knee joint injuries such as ligament ruptures and intra-articular fractures. It is directly related to the knee bend angle criterion in Figure Enough support must be provided below the main bumper to limit the bending angle to 15. Any support provided must not conflict with styling requirements or result in unacceptable low-speed [8 km/h (5 mph)] impact damage. 5-40

157 5.8.5 Design solutions As bumper systems meeting the requirements of pedestrian leg impact are only beginning to hit the marketplace in Europe, Australia and Japan, it is too early to identify the most popular designs. However, a thorough review of articles and patents does indicate the most popular design solutions for passenger cars. There is limited production of vehicles with exposed bumper beams (facebars) in these areas. Hence, there has been little activity devoted to adapting facebars to meet pedestrian impact requirements. For passenger cars with reinforcing beams, the most commonly proposed design solutions are: 1. Front End Vehicle Component Solutions a) Lower stiffener. A new component called a stiffener or spoiler may be located below the bumper system to prevent the lower part of the leg form from moving further toward the vehicle than the knee. The stiffener may be a fixed component or a component that deploys based on impulse or speed. b) Energy absorbers. To cushion impact, an energy absorber may be placed between the bumper beam and the pedestrian. Alternately, an energy absorber may be placed behind the bumper beam. The most commonly proposed energy absorbers are plastic foams (single or multi-density) and molded plastic egg crates. However, several proposed design solutions incorporate spring steel, composite steel/foam and crush can absorbers. c) Beam design. A tall -view bumper height may be used to provide leg support. d) Bull-bars. Structures may be added to the of an existing bumper system to provide energy absorption and to support the lower limb. 2. Sensor and Airbag Solution Any current bumper system may be covered with an airbag. In this way, the energy absorption capability of the bumper becomes irrelevant. The key disadvantages to this design approach are cost and sensor capability. All of the Front End Vehicle Component Solutions listed above may be used in conjunction with steel reinforcing beam bumper systems. The Sensor and Airbag Solution would appear to have the greatest potential for use with steel facebar bumper systems such as those used on pickup trucks. 5-41

158 FIGURE 5.10 EuroNCAP PEDESTRIAN TESTS (2010 ITERIA) Leg to Bumper Upper Leg to Hood Edge Head to Hood Top Knee bending < 15 Knee shear < 6 mm Tibia acceleration < 150 g Total load Bending moment < 5 kn < 300 Nm HIC < 1000 F u : Ped estrian I p c m co du 5-42

159 5-43 FIGURE 5.11 EuroNCAP LEG FORM IMPACTOR

160 FIGURE 5.12 EuroNCAP LEG FORM IMPACT ITERIA (2010) 5-44

161 6. Relevant safety standards in North America and Europe The bumpers on passenger cars sold in the United States must conform to United States National Highway Traffic Safety Administration (NHTSA) 49 C.F.R. Part 581 Bumper Standard (see Section 6.1). The bumpers on passenger cars sold in Canada must conform to Canadian Motor Vehicle Safety Regulations Section 615 of Schedule IV (see Section 6.2). This regulation states a bumper must meet the United States NHTSA Bumper Standard or ECE Regulation 42 as explained in Section 6.2 of this publication. Typically, although not mandatory, the bumpers on minivans sold in the United States and Canada meet the NHTSA requirements for passenger car bumpers. There are no federal regulations in the United States or Canada for bumpers on pickups, full size vans or SUVs. These bumpers are designed to meet OEM internal specifications. The Insurance Institute for Highway Safety (IIHS), in an effort to reduce the cost of passenger vehicle bumper repairs, has developed a test protocol that stimulates a broader range of impacts occurring in actual on-th-road crashes (see Section 6.4). The IIHS tests, conducted on passenger cars and minivans, are more severe that the NHTSA tests. The IIHS protocol is not a pass or fail protocol. Rather, it provides a weighted damage estimate that is used to determine the overall rating for a passenger vehicle. Many OEMs select a target overall rating for a vehicle to be sold in the United States and Canada. This target is used when designing the vehicle s bumpers. IIHS is currently conducting research and testing in order to develop a test protocol for SUVs and pickups. Most passenger vehicles sold in Europe have bumpers that conform to United Nations Economic Commission for Europe ECE Regulation 42 (see Section 6.3). Euro NCAP provides an independent assessment of the safety performance of cars sold in Europe. Pedestrian protection is an integral part of NCAP s overall rating scheme. Of particular significance in bumper design is the leg to bumper impact requirements in the Euro NCAP Pedestrian Protection Test (see Section 5.8.2). In addition, many European bumpers are voluntarily designed to perform well in Research Council for Automotive Repairs (RCAR) tests. RCAR s Low-Speed Offset Insurance Crash Test (see Section 6.6) was developed to prevent unnecessary damage to the structure of passenger cars in low- speed crashes. This test is now referred to as the RCAR Structural Test. Even if a vehicle performs well in the RCAR Structural Test, it may not exhibit good crash behaviour in real world accidents (often due to override or underride). To overcome this possibility, RCAR developed a test to assess how well a vehicle s bumper system protects the vehicle from damage in lowspeed impacts. This test is the RCAR Bumper Test (see Section 6.7). 6-1

162 6.1 United States National Highway Traffic Safety Administration (49 C.F.R.), Part Bumper Standard Requirements This standard (Reference 6.8) is summarized in Sections through The reader is cautioned that these sections are only a summary. The reader must refer to the actual regulatory document in order to obtain a complete understanding of the standard. The Bumper Standard only applies to passenger cars. A passenger vehicle is subjected to three impact procedures: 1. The pendulum corner impacts - and. 2. The pendulum longitudinal impacts - and. 3. The impacts into a fixed collision barrier - and. Following the three impact procedures, the vehicle shall meet the following damage criteria: 1. Each lamp or reflective device except license plate lamps shall be free of cracks and shall comply with applicable visibility requirements. The aim of each headlamp shall be adjustable to within the beam aim inspection limits. 2. The vehicle s hood, trunk and doors shall operate in the normal manner. 3. The vehicle s fuel and cooling systems shall have no leaks or constricted fluid passages and all sealing devices and caps shall operate in the normal manner. 4. The vehicle s exhaust system shall have no leaks or constrictions. 5. The vehicle s propulsion, suspension, steering and braking systems shall remain in adjustment and shall operate in the normal manner. 6. A pressure vessel used to absorb impact energy in an exterior protection system by the accumulation of gas or hydraulic pressure shall not suffer loss of gas or fluid accompanied by separation of fragments from the vessel. 7. The vehicle shall not touch the test device, except on the impact ridge shown in Figures 6.1 and 6.2, with a force that exceeds 2000 pounds (907kg) on the combined surfaces of Planes A and B (see Figure 6.3) of the test device. 8. The exterior surfaces shall have no separations of surface materials, paint, polymeric coatings, or other covering materials from the surface to which they are bonded, and no permanent deviations from their original contours 30 minutes after completion of each pendulum and barrier impact, except where such damage occurs to the bumper face bar and the components and associated fasteners that directly attach the bumper face bar to the chassis frame. 9. Except as provided in Criterion 8 (above), there shall be no breakage or release of fasteners or joints. 6-2

163 6.1.2 Vehicle Pendulum corner impacts Pendulum longitudinal impacts 1. The vehicle is at unloaded vehicle weight. 2. Trailer hitches, license plate brackets, and headlamp washers are removed. Running lights, fog lamps and equipped mounted on the bumper face bar are removed if they are optional equipment. 1. See Figure Impact speed of 1.5mph (2.4km/h). 3. Impact one corner at a height of 20 inches (500mm) using Figure 6.1 pendulum. 4. Impact other corner at a height from 16 to 20 inches (400 to 500mm) using Figure 6.2 pendulum. 5. Impact one corner at a height of 20 inches (500mm) using Figure 6.1 pendulum. 6. Impact other corner at a height from 16 to 20 inches (400 to 500mm) using Figure 6.2 pendulum. 7. The plane containing the pendulum swing shall have a 60 degree angle with the longitudinal plane of the vehicle. 8. Impacts must be performed at intervals not less than 30 minutes. 9. Effective impacting mass of pendulum equals mass of vehicle. 1. See Figure Impact speed of 2.5mph (4km/h). 3. Two impacts on surface, inboard of corner. 4. Two impacts on surface, inboard of corner. 5. Impact line may be any height from 16 to 20 inches (400 to 500mm). If height is 20 inches (500mm), use Figure 6.1 pendulum. If height is between 20 and 16 inches (500 and 400mm), use Figure 6.2 pendulum. 6. Pendulum Plane A (see Figures 6.1 and 6.2) is perpendicular to the longitudinal plane of the vehicle. 7. For each impact, the impact line must be at least 2 inches (50mm) in the vertical direction from its position in any prior impact, unless the midpoint of the impact line is more than 12 inches (300mm) apart laterally from any prior impact. 8. Impacts must be performed at intervals not less than 30 minutes apart. 9. Effective impacting mass of pendulum equals mass of vehicle. 6-3

164 FIGURE 6.1 IMPACT PENDULUM (20 Impact Height) (Source: Reference 6.8) FIGURE 6.2 PENDULUM (20-16 Impact Height) (Source: Reference 6.8) 6-4

165 FIGURE 6.3 SAMPLE IMPACT APPARATUS Source: Transport Canada, Safety and Security Sample impact apparatus with supports Sample impact apparatus without supports Plane B Impact Surface Plane A Weight equals unloaded vehicle weight +0, -10kg NOTES: 1. Drawing not to scale. 2. The arc described by any point on impact line shall be constant with a minimum radius of 3.3m and lie in a plane perpendicular to Plane A. 6-5

166 6.1.5 Impacts into a fixed collision barrier 1. Impact speed of 2.5mph (4km/h). 2. Impact into a fixed collision barrier perpendicular to line of travel while travelling longitudinally forward. 3. Impact into a fixed collision barrier perpendicular to line of travel while travelling longitudinally ward. 6.2 Canadian Motor Vehicle Safety Regulations Section 615 of Schedule IV This regulation (Reference 6.9) is summarized in Section The reader is cautioned that this section is only a summary. The reader must refer to the actual regulatory document in order to obtain a complete understanding of the regulation Requirements A passenger car shall be equipped with bumpers that conform to either: a) the requirements set out in title 49, part 581 of the United States Regulations or b) the requirements set out in paragraph 6, and the low-speedimpact test procedure set out in Annex 3, except for paragraph 4 of that Annex, of ECE Regulation No United National Economic Commissions for Europe ECE Regulation Requirements This regulation (Reference 6.10) is summarized in Sections through The reader is cautioned that these sections are only a summary. The reader must refer to the actual regulatory document in order to obtain a complete understanding of the regulation. The requirements apply to a vehicle with at least four wheels for the carriage of passengers comprising not more than eight seats in addition to the driver s seat. A passenger vehicle is subjected to two impact procedures: 1. The longitudinal test procedure with an impact device - two impacts at 4 km/h on the surface and two impacts at 4 km/h on the surface. 2. The corner test procedure with an impact device - one impact at 2.5 km/h on a corner and one impact at 2.5 km/h on a corner. After each impact test, the vehicle shall meet the following requirements: 1. The lighting and signalling devices shall continue to operate correctly and to remain visible. Bulbs may be replaced in the event of filament failure. 2. The hood, trunk lid, and doors shall be operable in the normal manner. The side doors shall not open during the impact. 3. The vehicle s fuel and cooling systems shall have neither leaks nor constricted fluid passages, which prevent normal functioning. Sealing devices and caps shall be operable in the normal manner. 4. The vehicle s exhaust system shall not suffer any damage or displacement, which would prevent its normal function. 5. The vehicle s propulsion, suspension (including tires), steering and braking systems shall remain in adjustment and shall operate in a normal manner. 6-6

167 6.3.2 Test vehicle Impact device 1. The protective devices and the mountings attaching them to the vehicle structure may be repaired or replaced between tests. 2. A vehicle of the same type may be used for each test. 3. Unladen weight means the weight of the vehicle in running order, unoccupied and unladen but complete with fuel, coolant, lubricant, tools and a spare wheel (if provided as standard equipment by the vehicle manufacturer. 1. The impact device is shown in Figure The impact device may be either secured to a carriage (moving barrier) or form part of a pendulum. 3. The effective mass shall be equal to the mass corresponding to the unladen weight of the vehicle. 4. With Plane A of the impact device vertical, the reference line shall be horizontal. 5. The reference line height is 445mm Longitudinal test procedure Corner test procedure Number of Number of Seating Positions Passengers Distribution 2 and in the seats 4 and in the seats 1 in the back seat 6 and in the seats 2 in the most seats 8 and in the seats 3 in the most seats When the row of seats has only two seating positions, one person shall be on the second row from the. 1. This procedure consists of four impacts at 4 km/h. 2. Two impacts are on the surface and two impacts are on the surface. 3. On each surface, one impact is made with the vehicle under unladen weight and the other is made with the vehicle under laden weight. 4. The choice of impact location for the first impact on each surface is free. The second should be at least 300mm from the first, provided the impact device does not overhang the corner of the vehicle. 5. Plane A of the impact device shall be vertical and the reference line horizontal at a height of 445mm. 1. This procedure consists of our impacts at 2.5 km/h. 2. Two impacts are on the surface and two impacts are on the surface. 3. On each surface, one impact is at one corner with the vehicle under unladen weight and the second impact is at the other corner with the vehicle under laden weight. 4. The choice of impact location for the first impact on each surface is free. The second should be at least 300mm from the first, provided the impact device does not overhang the corner of the vehicle. 5. Plane A of the impact device shall be vertical and the reference line horizontal at a height of 445mm./ 6-7

168 6-8 FIGURE 6.4 IMPACT DEVICE (Source: Reference 6.10)

169 6.4 Insurance Institute for Highway Safety: Bumper Test Protocol (Version VII) Requirements Test vehicles This protocol (Reference 6.11) is summarized in Sections through The reader is cautioned that these sections are only a summary. The reader must refer to the actual protocol document in order to obtain a complete understanding of the protocol. Four tests (a and a full-overlap test at 10 km/h and a and a corner test at 5 km/h) are conducted. After each test, a damage estimate is prepared as it would be done in a repair shop. A weighted damage estimate is calculated by adding the full-overlap damage estimate to the full-overlap damage estimate and multiplying the total by two; adding to this amount the corner damage estimate and the corner damage estimate; then dividing the grand total by six to get a weighted average damage estimate. The weighted average damage estimate is used to determine the overall rating for a vehicle. The good/acceptable boundary is $500, the acceptable/marginal boundary is $1,000 and the marginal/poor boundary is $1,500. However, no vehicle can earn a rating of good or acceptable if the vehicle is deemed undrivable or unsafe because of severe headlamp or tail lamp damage, hood buckling, coolant loss or the like. 1. Two vehicles are purchased to conduct the four tests. 2. The and license plate brackets (if provided) and all associated fasteners are removed. Bolt-on trailer hitch reinforcement members that are supplied as optional equipment are removed, but their fasteners are reattached to the vehicle where possible Impact barrier Full-overlap impact 1. The Impact Barrier is shown in Figure The bumper barrier is constructed of 12.5mm steel plate (Figure 6.6) and mounted to a block of reinforced concrete weighing 145,150 kg. 3. A steel backstop is constructed of 12.5mm steel plate (Figure 6.7). It is mounted to the upper surface of the bumper barrier ward from the impact face of the bumper barrier. 4. A plastic energy absorber is affixed by nylon push-pin rivets to the impact face of the bumper barrier. 5. An overlying plastic cover is mounted over the plastic energy absorber on the bumper barrier. 6. An overlying plastic cover is mounted over the steel backstop. 1. Two tests - into barrier and into barrier. 2. Impact speed of 10 km/h. 3. The forwarding portion of the bottom edge of the bumper barrier is 457mm from the floor. 4. At impact, the vehicle centerline is aligned with the bumper barrier centerline. 6-9

170 6-10 FIGURE 6.5 IIHS IMPACT BARRIER (Source: Reference 6.4)

171 FIGURE 6.6 STEEL BUMPER BARRIER (Source: Reference 6.4) FIGURE 6.7 STEEL BACKSTOP (Source: Reference 6.4) 6-11

172 6-12 FIGURE 6.8 OVERLAP FOR FRONT CORNER TEST (Source: Reference 6.4)

173 6.4.5 Corner impact 1. Two tests - corner into barrier and corner into barrier. 2. Impact speed of 5 km/h. 3. The forwardmost portion of the bottom edge of the bumper barrier is 406mm from the floor. 4. At impact, the vehicle overlaps the lateral edge of the barrier by 15% of the vehicle s width at the wheel wells (including moldings and sheet metal protrusions) at the corresponding axle - axle for corner test (Figure 6.8) and axle for corner test. 6.5 Consumers Union bumper basher tests This test (Reference 6.12), which is no longer used, consisted of impacting the and bumpers of a vehicle three times each. An impact bar, similar to that shown in Figure 6.4, was hydraulically propelled into the center, off-center and corner of the and bumpers. Following the six impacts, the total cost for parts and labor to repair the damage to the body and bumper for both the and of the vehicle were published in Consumer Reports magazine. The Consumers Union now relies on the IIHS Bumper Test Protocol (see Section 6.4). 6.6 Research Council for Automotive Repairs (RCAR) Low-Speed Offset Crash Test (Low-Speed Structural Test) This test (Reference 6.13) is summarized in Sections through The reader is cautioned that these sections are only a summary. The reader must refer to the actual test document in order to obtain a complete understanding of the test. RCAR states its purpose of this test is to determine a vehicle s damageability and repairability features Requirements Test vehicle Two impacts are conducted. The first is a 15 km/h (9mph) impact by the of the test vehicle into a fixed barrier with a 40% offset. The second is a 15km/h (9mph) impact by a mobile barrier, with a 40% offset, into the of the test vehicle. After each impact, the replacement parts required to reinstate the vehicle to its pre-accident condition are recorded. Also, the number of hours required to replace the damaged parts and to repair those items capable of repair, such that the vehicle is reinstated to the pre-accident condition are recorded. The cost of the replacement parts and the number of hours are estimated. Thus, the results of the crash test indicate the repairability and damageability status of the test vehicle. The test procedure applies to people driven passenber vehicles of up to 2.5 times mass. The test vehicle shall be previously undamaged and representative of the series production. The test vehicle for the impact may be the same vehicle used for the impact, provided the damage sustained during the impact has no effect on the results of the impact. 6-13

174 6.6.3 Front impact 1. One impact into a non-deformable barrier/former (see Figure 6.5). The former can be adjusted laterally to accommodate various vehicle widths. The former may be secured to a fixed barrier or placed on the ground with arresting devices to restrict its movement. The face of the former is perpendicular to the direction of travel of the test vehicle. The mass of the barrier/former exceeds twice that of the test vehicle. The steering column side of the vehicle contacts the former. The test vehicle overlaps the former by 40%. 2. The test vehicle impact speed is 15km/h (9mph) Rear impact 1. One impact by a mobile barrier into the test vehicle (Figure 6.6). The mobile barrier has a mass of 1000kg (2205 pounds). 2. The mobile barrier contacts the side of the vehicle opposite to the steering column side. The barrier overlaps the test vehicle by 40%. The barrier impact speed is 15 km/h (9mph). 6-14

175 6-15 FIGURE 6.9 RCAR FRONT ASH PROCEDURE (Source: Reference 6.13)

176 6-16 FIGURE 6.10 RCAR REAR ASH PROCEDURE (Source: Reference 6.13)

177 6.7 Research Council for Automotive Repairs (RCAR) Bumper Test This test is summarized in Sections through The reader is cautioned that these sections are only a summary. The reader must refer to the actual test documents (References 6.14 and 6.15) in order to obtain a complete understanding of the test. The RCAR Bumper Test encourages vehicle manufacturers to produce effective bumper systems that feature tall energy absorbing beams and crash boxes, that are fitted at common heights and can effectively protect the vehicle in low speed crashes. To this end, RCAR also publishes a Design Guide (Reference 6.16) to ensure good design practice for repairability and limitation of damage. The RCAR test applies to passenger cars, pickups and SUVs Requirements Bumper beams that have insufficient height will be presumed to fail the test. Also, bumper beams that use the barrier system backstop for energy management will be regarded as unacceptable. Bumper beams are likely to have insufficient height if the relevant bumper engagement is less than 75mm as shown in Figure For a bumper, the distance from the floor to the underside of the bumper barrier is 455mm. For a bumper, the distance from the floor to the underside of the bumper barrier is 405mm. Bumper beams with a relevant engagement less than 75mm will be tested if the qualifying bumper beam height is 100mm or more. Bumper beam height is measured in the center of the vehicle, in of the left siderail and in of the right siderail. The center of the vehicle bumper height is weighted 50%. The left and right siderail bumper heights are each weighted 25%. The sum of the three weighted heights is the qualifying bumper beam height. The test involves either the or of a moving car striking a fixed bumper barrier at 10 km/h. The centerline of the car is aligned with the center of the bumper. RCAR does not assign vehicle ratings. It states that results from the RCAR Bumper Test may be used by RCAR members (or the associated test organizations) for rating or consumer information purposes to suit local market conditions Bumper Barrier 1. The bumper barrier is shown in Figures The rigid bumper barrier is made from steel. It is 100mm deep and 1500mm wide. The flat face has a radius of 3400mm. The bumper barrier can be mounted at various heights to the unyielding and immovable crash wall. 3. A rigid steel backstop is fixed on top of the barrier. It has the same radius and width as the bumper barrier. 4. An energy absorber is firmly affixed to the face of the bumper barrier. 5. A cover over the energy absorber is wrapped around the bumper barrier and fastened to the top and bottom plane of the barrier. 6-17

178 6-18 FIGURE 6.11 RELEVANT BUMPER ENGAGEMENT (Source: Reference 6.14)

179 FIGURE 6.12 BUMPER BARRIER (Source: Reference 6.14) FIGURE 6.13 BUMPER BARRIER WITH BACKSTOP AND ENERGY ABSORBER (Source: Reference 6.15) 6-19