1. Current Applications of FE Simulation for Blanking and Stamping of Sheet Materials
Taylan Altan, Professor & Director
Center for Precision Forming – CPF (
Engineering Research Center for Net Shape Manufacturing
ERC/NSM – (
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. 0.15 Material Properties / Flow Stress Tensile Test (uniaxial)
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. 0.49 Material Properties/Flow Stress Bulge Test (biaxial)
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 by Tensile test and bulge test

10. Materials Tested with VPB Test at CPF
Steels and Stainless Steels
St 14
DP 780-CR
St 1403
DP 780-HY
AISI 1018
Bare DP 980 Y-type X
AKDQ
Bare DP 780 T-Si type
1050
GA DP 780 T- AI Type
DR 120
GA DP 780 Y-type U
DDS
GA DP 780 Y-type V
BH 210
 DQS-270F GA-Phosphate coated
HSS
 DQS-270D GA-Phosphate coated
DP500
SS 201
DP 590
SS 301
DP 600
SS 304
DP 780
SS 409
TRIP 780
AMS 5504
DP 980
Aluminum and Magnesium Alloys
AA 6111
AA 5754-O
AA 5182-O
X626 -T4P
AZ31B
AZ31B-O
Materials Tested at EWI-FC
AA-X620
270E
DP 980
TRIP 980
TWIP 980
TRIP 1180

11. Formability / Fracture in Bulge Test
SS304 sheet 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. Schematic of CDT Tooling at CPF/EWI
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. Higher BHF before fracture
Friction / Lubrication
Cup Draw Test
Lubrication performance:
Shorter Perimeter
Higher BHF before fracture 14

15. Blank holder force =16 ton
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. During Down Stroke, Cushion Pressure Generates Power
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. CPF die set ( for 160 ton press/ detailed drawings are available)
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
451.6 mm
R 4
598.4 mm
R 5
56.6 mm
R 6
41.6 mm
R 7
46.6 mm
R 8
51.6 mm 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
DIE
BLANK

25. STRETCH FLANGING
DIE
BLANK

26. SHRINK FLANGING
DIE
BLANK

27. CURVED U CHANNEL FORMING
BLANK
DIE

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. Quenched >27°C/s (~49°F/s) Less force and springback
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
Less force and springback
Mn-B alloyed steel
(As delivered)
Ferrite-Pearlite
Ref: Gutermuth 2011, Hall 2011. 26

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

31. Tailored B-Pillar with soft zone

32. Schematic of hole expansion (flanging)
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
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]
Conical with spherical tip
Single shear
Conical with flat tip
Humped 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
Al 5182-O, t0 = 1.5 mm
Flow stress from bulge
test
Preliminary tensile test simulations show that necking can be predicted:
by comparing load-elongation curves;
by finding the characteristic point (sudden increase in strain) 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 ph Please visit and for detailed information