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Current Applications of FE Simulation for Blanking and Stamping of Sheet Materials

Current Applications of FE Simulation for Blanking and Stamping of Sheet Materials. Taylan Altan, Professor & Director Center for Precision Forming – CPF ( www.cpforming.org ) Engineering Research Center for Net Shape Manufacturing ERC/NSM – ( www.ercnsm.org ) TTP 2013

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Current Applications of FE Simulation for Blanking and Stamping of Sheet Materials

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  1. Current Applications of FE Simulation for Blanking and Stamping of Sheet Materials Taylan Altan, Professor & Director Center for Precision Forming – CPF (www.cpforming.org) Engineering Research Center for Net Shape Manufacturing ERC/NSM – (www.ercnsm.org) TTP 2013 September 19-20, Graz, Austria

  2. OUTLINE • Introduction • Material Properties and Friction-Bulge, Dome, and Cup Draw Tests • Forming AHSS and Al in Servo Press • Hot Stamping (Press Hardening) of Boron Steels • Blanking/Piercing • Necking and Fracture Prediction • Conclusions / Future Work

  3. Center for Precision Forming(www.cpforming.org) Member Companies Aida Interlaken Altair (HyperMesh) IMRA - Japan Boeing Metalsa – Mexico Chrysler POSCO - Korea ESI North America (PAMSTAMP) Quaker Chemical EWI SFTC (DEFORM) Honda of America Shiloh Industries Hyundai – Korea Tyco Electronics

  4. Introduction / Major Trends To reduce weight and increase crash performance, in automotive production, AHSS, UHSS, Mn-Boron Steels (Hot Stamping) and Al Alloys are commonly used More complex materials require advanced material characterization and formability evaluation techniques (in addition to tensile tests) With increasing complexity of materials, for the same sheet material, variations in different heat lots, suppliers, plant locations and coils become a major issue Advanced lubricants and lubrication methods are critical Thus, methods for advanced precision design (simulation, die design and materials/coatings) and process control (servo presses, CNC multi-point hydraulic cushion, advanced lubricants) are needed

  5. Properties of Various Stamping Materials

  6. Material Properties / Flow Stress Tensile Test (uniaxial) 0.15 Ref: Nasser et al 2010

  7. Material Properties / Flow Stress Using real time measurements of pressure and dome height and FE Analysis Viscous Pressure Bulge Test (biaxial) Ref: Nasser et al 2010 7

  8. Material Properties/Flow Stress Bulge Test (biaxial) 0.49 • Tensile test gives a very limited information, • Bulge test gives more reliable strain-stress data. Ref: Nasser et al 2010 8

  9. Comparison of flow stress determined byTensile test and bulge test

  10. Materials Tested with VPB Test at CPF

  11. Formability / Fracture in Bulge Test SS304sheet material from eight different batches/coils [10 samples per batch] Highest formability  G , Most consistent  F Lowest formability and inconsistent  H

  12. Dome Test (LDH) / Flow Stress [Grote, 2009] • To obtain flow stress accurately, maximum thinning should occur at the apex of the dome as in Viscous Pressure Bulge test. • Flow stress is determined using Load-stroke curve and inverse FE analysis (also variable n in σ = KƐ n) 12

  13. Friction / Lubrication / Cup Draw Test (CDT) 12 inch Initial blank 6 inch Cushion Pins Deep drawn cup Schematic of CDT Tooling at CPF/EWI

  14. Friction / Lubrication Cup Draw Test Lubrication performance: Shorter Perimeter Higher BHF before fracture 14

  15. Cup draw test results for Al Blank holder force =16 ton Best lubricant Performance evaluation criteria for cup drawing test: (L1 is the best lubricant) The lubricants are evaluated based on (i) the perimeter of the flange and (ii) maximum blank holder force at which the cup can be formed without cracking. 15

  16. Friction / Lubrication / Temperatures Temperatures in deep drawing a round cup from DP 600 Higher contact pressure and higher temperature are detrimental for lubricants Ref: Kim et al 2009 16

  17. Forming in a Servo-Drive Press The flexibility of slide motion in servo drive (or free motion) presses. [Miyoshi, 2004] 17

  18. Servo Tandem Line at Suzuka (Japan) Plant (Honda)

  19. Servo-Hydraulic Cushion (Courtesy-Aida) During Down Stroke, Cushion Pressure Generates Power

  20. Potential Improvements in Forming with Servo Drive Presently, many stamping companies use servo drive presses to improve productivity (strokes/min) and reduce set-up time Ram deceleration (slow impact on blank, reduced forming speed (reducing temperatures, improving friction conditions) may improve formability and springback, especially with AHSS Slow ram speed improve edge quality in blanking Can the servo press help to improve the stamping conditions for AHSS (competition with Press Hardening)?

  21. Forming of Al alloy in Servo Press Die Design I (Thinning Distribution) Max thinning :22.1% 21

  22. Forming AHSS in Servo Press Die Design CPF die set ( for 160 ton press/ detailed drawings are available) Tool dimensions 22

  23. STRAIGHT FLANGING BLANK DIE R7 R8 R4 R3 The radii will be modified, based on results of FE simulations with DP 980 and DP 780. R5 R6

  24. U-CHANNEL DRAWING & U BENDING BLANK DIE

  25. STRETCH FLANGING DIE BLANK

  26. SHRINK FLANGING DIE BLANK

  27. CURVED U CHANNEL FORMING DIE BLANK

  28. FE MODEL OF A DEEP DRAWN PART FE predicted thinning distribution in the deep drawn part for die corner radius 7 mm, initial sheet thickness 0.83 mm, and depth of 30 mm.(DP600)

  29. Hot Stamping (Press Hardening) At ~950°C Austenite Easy to Form Quenched >27°C/s (~49°F/s) 3-5 min.s in Furnace Quenched Martensite Mn-B alloyed steel (As delivered) Ferrite-Pearlite Less force and springback Ref: Gutermuth 2011, Hall 2011. 26

  30. Tailored B-Pillar / Simulation Effect of blank holder design

  31. Tailored B-Pillar with soft zone

  32. Blanking and Hole Flanging • Schematic of hole expansion (flanging) • Schematic of blanking 32

  33. Blanking / Flanging • Hole flanging / edge cracking of advanced high strength steels (AHSS) is challenging because of the low formability of the material. • Edge formability / hole flangability can be improved by improving the blanked / pierced edge quality. • Higher flangability requires lower hardness (lower strain) on the blanked / pierced edge. • The optimum blanking parameters to obtain lowest hardness (and strain) on the blanked edge have to be determined for AHSS. • Terminology : Piercing – holes in the formed part • Blanking – cutting the large blank before forming 33

  34. Parameters Affecting Blanked Edge Quality and Hole Flanging • Punch/die clearance • Blankholder pressure • Punch tip geometry • Punch velocity (continuous or intermittent during blanking/possible use of a servo-press) These variables affect: hardness at and surface quality of blanked/pierce edge. Thus, they affect hole and edge flanging (possible cracks, Hole Expansion Ratio). 34

  35. Piercing / Punch Tip Geometry Conical with spherical tip Conical with flat tip Single shear Humped Several punch tip geometries can be compared to study their effect on strain distribution in the blanked edge. Single shear, double shear and conical were evaluated by [Shih, 2012]. Humped punch design was suggested by [Takahashi et al., 2013] 35

  36. Improving Tool Life in Blanking Experiments by [Högman 2004] • Sheet material - Docol800 DP, 1mm thick. • Punch material – Vanadis 4, 60 HRC • Punch wear from experiments correlate with punch stress from FEA. (a) Uniform clearance (b) Larger clearance Chipped after 40,000 strokes No chipping after 200,000 strokes Maximum Punch Stress (Simulations at ERC/NSM) 2010 MPa 2270 MPa [Högman, 2004] Punching tests of ehs- and uhs- steel sheet. Recent Advances in Manufacture & Use of Tools & Dies. October 5-6, 2004, Olofström, Sweden 36

  37. Prediction of Necking / Tensile Test Simulations Thinning progression Preliminary tensile test simulations show that necking can be predicted: by comparing load-elongation curves; by finding the characteristic point (sudden increase in strain) Al 5182-O, t0 = 1.5 mm Flow stress from bulge test 37

  38. Strain vs. stroke in cup drawing Material SS304

  39. Summary / Future Outlook New AHSS – first generation (DP, TRIP), second generation (TWIP) and variation / third generation (CP, MS) Hot Stamped versus second and third generation UHSS as well as Al alloys / cost and investment issues Use of Servo-Drive Presses with traditional steels, AHSS and Al alloys, also for blanking (ex. VW/Fagor) Warm forming of Al alloys and AHSS (?) Use of advanced methods and reliable input data for FE simulation / consideration of temperatures affecting flow stress and formabililty

  40. Questions/Comments Taylan Altan (altan.1@osu.edu) ph +1-614-292-5063 Please visit www.ercnsm.org and www.cpforming.org for detailed information

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