Die Steel Improvements for AHSS Applications

Transcription

1 Die Steel Improvements for AHSS Applications Thomas Bell HITACHI METALS LTD Arlington Hts, IL GDIS2018

2 AGENDA 2 HITACHI Intro Steel Production Methods for Die & Tooling Steels Typical Failure modes of Die Steels for AHSS Solutions to improve Tooling Performances Steel Types, Coatings Hot Stamping Die Steels Pre Hardened Die Steels Grain Oriented Die Steel Study

3 HMA NA Group Location Office / Sales S-Company G-Company F-Company C-Company Waupaca Foundry P-4 Waupaca Foundry P-1/2/3 Waupaca Foundry P-E Waupaca Foundry P-5 HMA-CG Waupaca Foundry P-L/W HMA-NY HMA-DT HCA-New Hampshire HTP-Meds Ward AAP HMA-SJ Waupaca Foundry P-6 HCA-Indiana Diehl Tool Steel Metglas Hitachi Metals North Carolina HCA-Florida US consolidated employees :8,012people (Including Japanese expats 40 people) Number of Offices :4 Sales offices, 19 Factories HC Queretaro 3 3

4 Hitachi Tool Steel Manufacturing Process Ask Your Tool Steel supplier Test Certifications (actuals from Mill Source ) Method of Manufacturing Forged, Rolled, etc. Recommended Heat Treat 4 4

5 Elongation (%) Sheet Metal (Part Material) Trends ~ ~ ~2015 IF 2015 & Beyond Tensile Strength MPa Cast Iron Or Steel Castings S7 / A2 / D2 Castings to Wrought Advanced Tool Steels Advanced grade die materials are needed for forming AHSS. Die Standards have not kept up with increased strength trend 3D?

6 3 Common Failure Modes 1) Chipping: Toughness is required for trims, flanges, pierce & punches Die Forming Direction Mechanism 1Burr occurs Work Shear 2Increase Friction 3Tensile Stress 5Chipping 4Cracking Lateral Shear 2) Galling: Galling resistance Forming Die Mechanism Friction Work Galling tends to occur at heavy loaded area 1Heated up by friction Die 2Alloying (Adhesion) 3Fall Away 6

7 7 Failure Mode 3) Wear: Surface Coating advancements have greatly improved steel performances Lateral Edge Hard Particle (Oxide, hardened steel, etc..) Punch Friction

8 Part material Aluminum or Steel: What type & thickness? Press Size (Servo or Mechanical) & Strokes per minute cycle Current Die Construction Progressive or Transfer? Castings? Inserts? Tooling steels used? What coating? Die Clearance Heat Treating Recipe Welding (In House? Outsource? Consumable used?) Failure Observations: What Happened? What's been tried so far? 8 Questions about Stamping Die Application Solution & Engineering Center Matsue, Japan

9 Standard Grades for Tooling Chemical composition (%) Grade C Si Mn Cr W Mo V Ni A AISI JIS DIN D S7 D SKD DIN M2 A SKD Din H13 S N/A N/A MATRIX : YXR H13 SKD61 DIN SLD Magic ** ** * 8% Cr M SKH DIN

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11 Microstructure D2 SLD-i Coarse & directional carbide Large & anisotropic deformation after heat treatment Medium galling & wear resistance Characteristics will be affected by grain direction μm Small, dense & homogeneous carbide Small & isotropic deformation after heat treatment Same HT & Chem as D2 Good galling & wear resistance Achieve higher hardness than D2/1.2379

12 Bending test Conditions Dies Polished by #8000 paper (2-4μm) Hardness:60HRC 12 Bead Load Initiation point and direction of galling Punch Die Work piece: HSS 980MPa 1.4mm Thick Schematic diagram of test condition Work piece after test

13 Abrasive Wear Test Conditions Pin-on-disc method(astm G99-05) Pin Disc Test piece Item Disc Grade Hardness Surface pressure Friction Speed Condition D2, SLD-i, and 8Cr 60,62HRC Alumina 7.8 MPa 0.42 m/s Specific wear rate( 10 14,m 2 /N) Results 60HRC 60HRC 60HRC 62HRC 60HRC SKD11 AISI D2 開発鋼 8%Cr 鋼 Friction length 377 m SLD-i 13

14 SLD-i SLD-MAGIC 14

15 Test results of SLD-MAGIC by customers Product : Liquid crystal panel parts Forming : Blanking Present: 8%Cr steel Work material : SS 3 mm thick Grade Hardness Heat treatment Distortion Machinability Life Damage Present 8%Cr steel 60~62HRC Temper % Normal 30,000 hits Burr(wear out) Less wear Die life 30%UP S-MAGIC 60~62HRC Temper ~0.02% Good >40,000 hits Small wear(carry on) 15

16 Test results of SLD-MAGIC by customers Product : Automobile parts Forming : Blanking Present: D2 Work material : 780MPa AHSS : 1.8 mm (SLD-MAGIC)Small crack Possible to repair by welding Die life is longer Present SLD-MAGIC Grade Hardness Heat treatment D2 58~60HRC Temper ~60HRC Temper 170 Life 6,000~15,000shots >40,000shots repaired by welding large crack at 25, 000 hits 16

17 Heat Treatment Deformation Minimization 17 17

18 Distortion on SLDi vs D2 D2 18

19 Example Part material 2.5 mm thick Aluminum Before test: D2 had to be 80,000 strikes due to galling Re-Polish, re-coated Start SLDi (HITACHI D2) Test SLD-i material (Hitachi Metal) Full Harden 62HRC only Maintain steel polish 1/ month (Ave. 65,000 hit) Maintenance time reduced to 83% from original condition SLDi steel is better result than D2+Coating 19

20 Concept of Pre- Hardened Die Steels D2 Machining Heat Treat Finishing Coating TD/CVD Annealed Hardened 60HRC ~ 510 Adjust Rework Mass- Production Customer's Process SLD-F NEW STEEL Machining Finishing Trial use Coating PVD Customer's process Hardened Rework ~510 Mass- Production

21 Machining of Pre-Hard Tool 60 HRC 1) Machine Tool Rigid Construction: High Spindle Speed:20,000+ 2) Cutting Tool Solid Carbide with ductile properties for interrupted cut 3) Consistent substrate of Die Steel

22 Effect on Machinability Table. Chemical composition (mass%) C Si Mn S Cr Mo V Al Nb SLD F Lower than D2 Higher than D2 Higher than D2 Trace Lower than D2 Higher than D2 Trace Trace - D Cr(A) Cr(B) Trace Trace Decreasing carbides Belag formation -SLD- F has good machinability 60HRC due to less primary/ secondary carbide. -In order to prevent the wear and improve the life of die, 100μm PVD coating on the surface of the dies is recommended. A sample microstructure of SLD- F

23 Mechanism of better machinability Chip Die steel Carbide Cutting tool Cause of tool wear and chipping -Adhesion of die steel -Cutting resistance by carbides Less Carbide Belag Formation Carbide Die steel Belag formation becomes the protective coat for cutting tool Cutting Tool Being less the carbide contribute to being less cutting resistance. Oxide layer formation called Belag on the surface of the cutting tool during cutting plays prevent the cutting tool from chipping. Chip Cutting tool

24 Simulation : Process cost and lead time of Pre-Hard PROCESS Time Time Cost Cost D2 Annealed SLD F New Steel D2 Annealed SLD F New Steel + HT Pre-hard 60 HRC + HT Pre-hard 60 HRC Raw Steel $600 $1,105 Drilling.5 Hr. 3.5 Hrs. $240 $1,440 Milling 10 Hrs. 16 Hrs. $4,160 $6,260 HT Prep 2 Hrs. 0 $290 0 HT 72 Hrs. 0 $245 0 Fin Mach. 12 Hrs. 12 Hrs. $2, Hrs. 31 Hrs. $7,535 $8,805 Condition of simulation Material weight : 160 lbs. 200T 200W 160 M16 hole x 5 locations M16x25H tapped hole x 2 locations

25 Lead Time comparison : DieMaker (Automotive) in Japan Total process time for die-making Improvement (Decrease in lead time) Die size; mm (50kg) Drilling Rough machining Surface grinding Polishing for shape correction Finish machining Wire cutting

26 HOT STAMPING 1200 MPA + Demands on Die Materials Wear Conductivity Watch for industry developments on 3D Additive Mfg. inserts w/ conformal cooling lines Use of higher alloyed Die Steel 26

27 Hot Work Die Steels: NADCA Rated 27

28 HOT STAMPING DIE MATERIALS Upgrade to a NADCA Class C Hot Work Steel in place of AISI H13 1. Conductivity Class B H13 is 600C Class C is 600C 2. Toughness: 3. Wear: 4. Coatablity Better for heat conductivity than H13 means better cycle times. Why? Higher Impact Values (charpy) prevent cracking on the surface of Hot Stamping Dies close to the cooling channel. Why? NADCA Class C ( HITACHI DAC-MAGIC ) is higher strength under high temperature. Die surfaces can reach ~ 400C & higher alloyed steels are needed to extend wear. Coatable and Wear resistance at room temperature, almost same as H13. 28

29 Yield, Tensile Strength and Impact Strength Room temperature Grade C Yield strength Tensile strength Yield strength Tensile strength 12 Grade C DAC-Magic NADCA Class C Charpy Impact (ft.-lbs.) 8 4 Grade B Grade B 4% Better 2.5% Better 5% Better 12% Better NADCA Class B (H13) DAC- H13 DAC-Magic Magic Average value DAC- H13 DAC-Magic Magic Minimum value 2V-notch Charpy impact test results (ft.-lbs.) 29 Hitachi Metals, Ltd. All rights reserved.

30 CrWN 30

31 DOES GRAIN DIRECTION ON DIE INSERTS MATTER? What is anticipated highest Impact Area? Is Grain direction detectable? Can this detail be marked? 31

32 EXAMPLES of GRAIN Rolling or Forging Direction 32

33 Orientation Diagram Arrows indicate the direction of the impact force 13.7 ft.-lbs. D2 3.0 ft.-lbs. Transverse 4.0 ft.-lbs. Short transverse (into the page)

34 Impact Toughness Tests: Short-Transverse NADCA Class C Mod HW DAC Magic NADCA Class B Prem H13 DAC P 8% Cr SLD Magic D2 M2 SLDi Ft Lbs HRC Tested

35 Conclusions Review Die Standards & allow for areas requiring better tooling steels in trouble-spots Compare results with other steels in side by side likeenvironments Insist on controlled HT path & Welding steps Ask for grain orientation on larger cross sections If you can t use a better tool steel, use your tool steel better 35

36 THANK YOU Thomas Bell HITACHI METALS LTD Sources for More Info Exova Element Lab For More Information Mitsubishi Hitachi Tool Ceratizit Carbide & HB Carbide BayCast AutoSteel Partnership: Great Designs in Steel TCI Coatings in Olivet, MI Schuler 36