DEVELOPMENT OF ANTI-ROLL BAR BY HYDRO-FORMING TECHNIQUE

Transcription

1 DEVELOPMENT OF ANTI-ROLL BAR BY HYDRO-FORMING TECHNIQUE Ajay Katiyar, Sudhanshu Mishra, Amit Saxena 1 Department of Mechanical Engineering, Maharana Pratap Engineering College, Kanpur (U.P.), India 2 Department of Mechanical Engineering, Dyalbagh Educational Institute, Agra, India 1 Phone No , 1 ajay_cim@rediffmail.com, Abstract When carried to the extreme, today's emphasis on automobile mass reduction has significant implications for vehicle ride and suspension design. Value Engineering is a systematic method to improve the "Value" of goods and services by using an examination of function. Value, as defined, is the ratio of Function to Cost. Value can therefore be increased by either improving the Function or reducing the cost. In this project attempt is made to develop the anti roll bar with hollow cross-section (replacing the solid cross section) by tube hydro forming technique thereby reducing the cost without any change in the performance of anti roll bar.stabilizer bars, also known as anti-roll or anti-sway bars, play a significant role in the modern day suspension systems by providing additional roll stiffness during sharp cornering and other rolled-over conditions 1.0 Tube Hydro-Forming Manufacturing Technique For Anti Roll Bar Tube hydro forming is a manufacturing process that uses water or hydraulic fluid to change a metal tube into the desired final shape. In hydro forming, a metal tube is bent to a rough shape before hydro forming; the tube is then put into the hydro forming die. The die is closed and hydraulic pressure is applied. The tube expands into the die and takes its final shape. Tube hydro-forming is relatively inexpensive, although an expensive press is required because often the number of manufacturing steps for a component, material used for the part as well as the amount of scrap metal can be reduced. Also, due to the lower number of manufacturing steps required, the labor-requirements are decreased as well. Although much research still needs to be done to increase the confidence of engineers in this shaping process, it is already being implemented in new designs and is being increasingly used for critical components. Tubehydro-forming is generally considered one of the most important manufacturing techniques in decreasing weight and therefore fuel-consumption of cars in the future. Tube hydroforming was invented approximately 40 years ago but has only recently Gained popularity and is moving from being a pure research activity to an applied manufacturing process. Tube hydroforming is especially popular in the automotive industry. Hydroforming can be used for both tubes and sheets. Also, hydroforming can be classified as low-pressure and high-pressure hydroforming. One major area where tube hydroforming is applied is in automotive structures and not only can stiffness of a car be achieved through design using tube hydroforming, but the part count can also be reduced and the assembly can be simplified especially form the tooling requirements. Automotive applications include radiator enclosures, space frames, dash assemblies, frame rails, engine cradles and other sub-assemblies. Production numbers of tube-hydro formed applications have increased dramatically over the years; they are currently being used on sports cars that are produced at low production rates as well as pick- up trucks and sport utility vehicles that are produced at much higher production rates. Automobile manufacturer General Motors claims that the GM Siverado frames is the most intelligently engineered frame GM has ever produced. The front frame is made of tube hydro formed rails. In the Silverado frame, over 20 kg (44 lb) of material were saved and the amount of scrap was reduced. 2.0 Tube Hydroforming Process Tube hydroforming is a process that pressurizes water or hydraulic fluids inside a tube to produce a tubular component with added features that were not possible or very complicated to manufacture with other more traditional techniques. A prebent and pre-cut section of seam-welded, cold-rolled steel tubing is placed in a closed die set where the pressurized fluid is introduced into the ends of the tube (see Figure 1). The tube is therefore reshaped to the contours of the cavity. Components range from approximately 1 to 3 meters (3 to 10 ft) in length and 25 to 150 mm (1 to 6 in) in diameter. Generally the aim is to produce components that are lighter, stronger, and require fewer pieces than traditional stamp-and-weld components. To date, one of the largest 1

2 hydroforming presses is located at Schuler SMG GmbH & Co. KG in Wilmsdorf, Germany. The press has a nominal press force of KN and can form tubes up to 6 meters in length. In conventional hydro forming, the part needs to be annealed and extensively lubricated. In the Vary-Form process, the part does not need to be annealed nor does it need to be lubricated. The prepared part is then placed inside the die. In some processes, a low hydraulic pressure is applied as the die is being closed (see Figure 2). This low pressure reduces die friction; assuring uniform wall thickness and better calibration of the process for the high-pressure stage (see Figure 3). When the die is closed, the high pressure is applied. The tube expands to completely fill the sides of the tubes. During the high pressure stage of the Vary- Form process, punches located in the die. This reduces stretching and other unwanted deformations. Also, slides can be inserted into the die at this point to provide indented surfaces in the tube walls (see Figure 4). There are two established pressure regimes, known as low-pressure and high-pressure hydroforming. According to the Tube and Pipe Fabricators Association, up to and including 83 MPa (12000 psi) hydroforming is known as low-pressure and above this point it is known as high-pressure hydroforming. The pressure required is determined by the complexity of the part. Generally, the more complex the shape, the higher the required pressure will be. If less than 5% constant pressure expansion is required to shape the part, low-pressure tubehydroforming will accomplish the shape change desired. If 5% to 25% constant pressure expansion is required, or wrinkles must be removed, high-pressure tube hydroforming becomes necessary. Equipment for the process is expensive and needs to be calibrated. Also, many presses are very large. This has hindered hydroforming from being used on a larger scale than it currently is. According to Automotive Design and production, The CHF (short for Compact Hydro Forming) from AP&T Tangent is much like a standard hydroforming press, except that it's much smaller about 60% smaller than conventional machines, says 2

3 AT&T s CHF developers. Although this is a small die, users are not limited to small parts. If the dies are reengineered and a forming sequence is decided, large parts can be formed. Another problem that stopped hydroforming form being more popular is the thinning and wrinkling that can occur when hydroforming complex parts. The process is slowly being refined to deal with this problem. One company (Vary-Form in Warren, MI), uses a two-stage sequential pressure process. Both water and die pressure are varied to slowly reshape the metal to its final form. According to Vary-Form, by employing this varying pressure method, pressures overall are lower, causing less stress to the metal. Also, with this method, outside corner radii of two times the metal thickness can be achieved. To better control the reaction of the part to the hydraulic pressure, the work piece can also be compressed. Besides this experimental use, Vary-Form produces various components for current automotive applications (see Figure 5). In the future many cars may employ a space frame design. A space frame is a series of structural members that are assembled and support all interior and exterior components of a vehicle. There are several problems associated with this structure, which have prevented it from being more widely used: it has proven difficult to mass-produce cost-effectively. The major problems can be summed up into three components: dimensional instability, design inflexibility and manufacturing cost. As previously discussed, tube-hydroforming is a manufacturing technique that can help on all three problems. One current production mass-model (70000 cars/year) that uses the space frame design is used on the Audi A2. Eleven tube-hydro formed components are built into this structure. 3.0 Problems Preventing Wide-Spread Use One of the major problems that prevent wide spread use of hydroforming are plain and simple resistance to change. Engineers are more comfortable to keep using methods (in this case stamping and welding) that they are familiar with. Also, the tooling already is installed at the factories to manufacture using the old techniques. Another major problem that must be overcome is the lack of a knowledge base for manufacturers to use. Tremendous strides have been made in recent years to increase knowledge. To overcome these hurdles two methods are suggested: more biaxial stress testing and modeling using numerical methods. Until today, many researchers use unaxial tensile tests to determine the properties of tube material for hydroforming. Since tubes are pre-bent (thereby introducing axial stresses) and then hydro formed (mostly circumferential stresses) there is a large variation in strain path from the uniaxial tensile tests. The Engineering Research Center for Net Shape Manufacturing (ERC/NSM) at the Ohio State University has developed a biaxial bulge test. The original test can be used with many metals but requires expensive tooling. More recently, the ERC/NSM has come up with a more inexpensive test. This test may be used in the future to collect more information for hydroforming purposes. It is even inexpensive enough, that it could be used to control the quality of incoming parts from a subcontractor. Numerical simulation can be used to gain knowledge in simulating hydroforming and hydro formed material properties. To gain confidence in the system, designers must compare the numerical and experimental results. When enough testing and fine-tuning has been done, the manufacturability and performance could be predicted using a numerical approach. This would cut down costs and increase performance and manufacturability of tube-hydro formed components. 3

4 4.0 Special Attention during Manufacture Because of torsion member s being heavily dependent on the outside diameter, constant geometric shape is required. This can be harder to achieve in tube materials than in solid materials. Usually requiring the use of a filler material so not to crush the tube while in the bending process. Reliable hand manufacture of these types of Anti- Roll bar is next to impossible; the use of mandrels to bend the tube becomes essential. The tubehydroforming process is capable of forming parts that are not easily made using traditional forming techniques. In the tube-hydroforming process, pre-bent parts are placed into dies. The dies are closed and water or hydraulic fluid is introduced into the tube under pressure. The pressure bulges the tube outwards against the die. Holes can be punched in this stage as well. By using hydroforming, the number of parts for many assemblies can be reduced, and therefore also the stiffness of the assembly. Also, hydroforming has reduced tooling costs compared to traditional manufacturing methods, better part integration, eliminates pinch weld flanges, reduced die wear, less scrap because dimensional repeatability is increased and less mass because by using less parts the same stiffness can be achieved with less material. Traditional tube-hydroforming can be done with a limited number of steels and aluminum alloys. More recently techniques have even been developed to make better use of less-expensive materials, including low carbon hot rolled steel, cold rolled steel, high strength low alloy steels, galvaneal and aluminum alloys for hydroforming purposes. As a result of the reductions in tooling and material requirements, the tube-hydroforming process has the potential to reduce production costs and increase performance of components at the same time. This combination of possibilities is leading to an increased number of components in automobile structures being produced out of tube-hydroforming. According to one estimate, by % of all vehicles produced will contain some hydro formed parts. Before tube-hydroforming can gain universal and wide-spread use, it must be researched to increase knowledge and confidence in the process. 5.0 Comparision with Different Diameters (By Bending Equation) Strength Comparison By Bending Equation Non-Dimentional Consta nt Hollow 45 Hollow 45.1 Hollow 45.2 Hollow45.3 Hollow 46.3 Hollow 47.3 solid Hollow 48.3 hollow 49 Hollow 50 Hollow 55 Hollow 60 Hollow 65 solid 55 solid solid 50 solid 65 hallow 70 hallow90 hallow 80 hallow 100 hallow110 hallow120 hallow 130 solid 60 hallow85 hallow 75 hallow95 hallow105 hallow115 hallow Diameter 4

5 Strength Comparision By Torsional Equation Hollow 45 Hollow 45.1 Hollow 45.2 Hollow45.3 Non-Dimensional Constant Hollow 46.3 Hollow 47.3 solid Hollow 48.3 hollow 49 Hollow 50 Hollow 55 Hollow 60 Hollow 65 solid 55 solid solid 50 solid 65 hallow 70 hallow90 hallow 80 hallow 100 hallow110 hallow120 hallow 130 solid 60 hallow85 hallow 75 hallow95 hallow105 hallow115 hallow125 hallow Diameter 6.0 Conclusion It can be stated that weight reduction of anti roll bar can be done without change in strength by using hydroforming technique. Thus a 55 mm dia antiroll bar can be replaced by corresponding hollow tube with outer dia 70mm and thickness 5 mm thereby reducing weight by 60 %.Case study for hydro forming technique is done for 5 mm tube and maximum pressure required to achieve the bending is found to be 15 Mpa. References 1. Sampson, D., Active Roll control of articulated heavy vehicles, University of Cambridge. UK, Quirke, Jennifer. Hydroforming What s all the Commotion? Modern Metals. August Pages Call number: PM TS 200 M Knowing about Forming. Automotive Design and Production. Internet: World Wide 5. Web April Vary-Form, the Leader in Hydroforming Technologies. Vary-Form. Internet: World 7. Wide Web April Hydroforming. Schuler AG. Internet: World Wide Web orming/haupt_frame.htm. 02 April L.N.B. Gummadi, H. Cai, S. Lin, X. Fan and K. Cao, "Bushing Characteristics of Stabilizer Bars", Paper No , SAE International Congress and Exposition, ABAQUS User's manual, Version 6.3, HKS Inc,