Blanking and Stamping of Sheet Materials · – Hot Stamping (Press Hardening) of Boron Steels –...

Sheet Forming Group © Copyright Engineering Research Center for Net Shape Manufacturing, 2013

CPF

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

http://www.cpforming.org/

http://www.ercnsm.org/


CPF

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


CPF 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

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CPF 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

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CPF Properties of Various Stamping Materials

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0 200 400 600 800 1000 1200 1400 1600 1800 20000

10

20

30

40

50

60

70

Ultimate Tensile Strength (MPa)

Tota

l E

longation

(%)

Aust

.

SSTRIP

TWIPIF

Mil

d BH

CM

n

MART

L-IPMild Steels

Conventional High Strength

Steels

Advanced High Strength Steels

2nd Generation AHSS

Aluminum alloys

AlAl

(hs)

Lightweight Potential*

Higher forces & springback*

Bett

er

Form

abili

ty

* Steel to steel comparison.

Al has lower density (more

lightweight potential) and lower E-

modulus (more springback)

compared to steel with similar

strength.


CPF Material Properties / Flow Stress

Tensile Test (uniaxial)

Ref: Nasser et al 2010

0.1

5

6


CPF

Ref: Nasser et al 2010

Material Properties / Flow Stress

Using real time measurements of pressure and dome height

and FE Analysis

Viscous Pressure Bulge Test (biaxial)

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CPF

1) Tensile test gives a very limited information,

2) Bulge test gives more reliable strain-stress data. Ref: Nasser et al 2010

Material Properties/Flow Stress

Bulge Test (biaxial)

0.4

9

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CPF Comparison of flow stress determined by

Tensile test and bulge test

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0 0.1 0.2 0.3 0.4 0.50

200

400

600

800

1000

True Strain

True Stress (MPa) True Stress (ksi)

29

58

87

116

145

VP Bulge Test

Tensile Test

Uniform Strain

from Tensile

Test = 0.16

Tensile data with Power Law

(σ=Kεn)

Useful strain

from Bulge

Test = 0.49

Material, DP600, t0 =1 mm


CPF

Materials Tested with VPB Test at CPF

Aluminum and Magnesium Alloys

AA 6111

AA 5754-O

AA 5182-O

X626 -T4P

AZ31B

AZ31B-O

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

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Materials Tested at EWI-FC

AA-X620

270E

DP 980

TRIP 980

TWIP 980

TRIP 1180


CPF

Highest formability G , Most consistent F

Lowest formability and inconsistent H

SS304 sheet material from eight different batches/coils

[10 samples per batch]

Formability / Fracture in Bulge Test

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CPF Dome Test (LDH) / Flow Stress

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)

[Grote, 2009]

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CPF

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Schematic of CDT Tooling at CPF/EWI

Initial blank

Deep drawn

cup

12 inch

6

inch

Friction / Lubrication / Cup Draw Test

(CDT)

Cushion Pins


CPF

Shorter

Perimeter

Higher BHF before fracture

Cup Draw Test

Lubrication performance:

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Friction / Lubrication


CPF

L1 L2 L3 L4 L5 L6 L7

715

720

725

730

735

740

745

750

755

Lubricant code

Fla

ng

e P

eri

me

ter

(mm

)

Cup draw test results for Al

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.

Blank holder force =16 ton

Best lubricant

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CPF

Ref: Kim et al 2009

Temperatures in deep drawing a round cup from DP 600

Contact area with die

Higher contact pressure and higher temperature are detrimental for

lubricants

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Friction / Lubrication / Temperatures


CPF Forming in a Servo-Drive Press

The flexibility of slide motion in servo drive (or free motion) presses. [Miyoshi, 2004]

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CPF

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Servo Tandem Line at Suzuka (Japan) Plant

(Honda)


CPF

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Servo-Hydraulic Cushion

(Courtesy-Aida)

During Down Stroke, Cushion Pressure Generates Power


CPF 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)?

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CPF Forming of Al alloy in Servo Press

Die Design I (Thinning Distribution)

Max thinning :22.1%

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CPF

Tool dimensions

CPF die set ( for 160 ton press/ detailed drawings are available)

Forming AHSS in Servo Press

Die Design

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CPF STRAIGHT FLANGING

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DIE

BLANK

R7

R3

R6

R4

R5

R8

R 3 451.6 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

The radii will be

modified, based on

results of FE simulations

with DP 980 and DP 780.


CPF

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U-CHANNEL DRAWING & U BENDING

DIE

BLANK


CPF

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STRETCH FLANGING

DIE

BLANK


CPF

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SHRINK FLANGING

DIE

BLANK


CPF

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CURVED U CHANNEL FORMING

BLANK

DIE


CPF

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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)


CPF Hot Stamping (Press Hardening)

Ref: Gutermuth 2011,

Hall 2011.

Mn-B alloyed steel

(As delivered)

Ferrite-Pearlite

At ~950°C

Austenite E

asy t

o F

orm

Less force and

springback

Quenched

Martensite

3-5 min.s

in

Furnace

Quenched

>27°C/s (~49°F/s)

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CPF Tailored B-Pillar / Simulation

Effect of blank holder design

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CPF Tailored B-Pillar with soft zone

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Estimated UTS (MPa)

Min = 924

Max = 1591

1000

900

1600

1500

1400

1300

1200

1100

UTS = 920-1020 MPa

UTS = 1500-1590 MPa


CPF

Schematic of hole

expansion (flanging) Schematic of blanking

Blanking and Hole Flanging

vp=punch velocity fb=blankholder forceθ=punch angle (conical) dd=diameter of the diedb=diameter of blankholder rd=die radiusdh=diameter of pierced hole in the blankdp=punch diameter (hemispherical)

Punch

θ

dp

dd

rd

db

vp

fbBlank Holder

DIE dh

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CPF 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

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CPF 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).

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CPF

• 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]

Single shear Conical with flat tip Humped

Piercing / Punch Tip Geometry

Conical with

spherical tip

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CPF Improving Tool Life in Blanking

Experiments by [Högman 2004]

[Högman, 2004] Punching tests of ehs- and uhs- steel

sheet. Recent Advances in Manufacture & Use of Tools

& Dies. October 5-6, 2004, Olofström, Sweden

• 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

Chipped after 40,000 strokes No chipping after 200,000 strokes

Maximum Punch Stress (Simulations at ERC/NSM)

2010 MPa 2270 MPa

(b) Larger clearance

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CPF Prediction of Necking / Tensile Test Simulations

Preliminary tensile test simulations show that necking can be

predicted:

(a) by comparing load-elongation curves;

(b) by finding the characteristic point (sudden increase in strain)

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0 10 20 30 40 500

0.5

1

1.5

2

Thic

kness S

train

()

Time(sec)

0 2 4 6 8 10 12 140

2

4

6

8

10

12

Load (

kN

)

Elongation (mm)

Simulation

Experiment

Al 5182-O, t0 = 1.5 mm

Flow stress from bulge

test

Thinning progression


CPF Strain vs. stroke in cup drawing

Material SS304

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Insulation plate

Die ring

Heaters

Blank holder

Water inlet

Cushion pins

Punch

Sheet


CPF 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

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CPF Questions/Comments

Taylan Altan

([email protected])

ph +1-614-292-5063

Please visit www.ercnsm.org

and www.cpforming.org

for detailed information

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mailto:[email protected]

http://www.ercnsm.org/

http://www.cpforming.org/

Blanking and Stamping of Sheet Materials · – Hot Stamping (Press Hardening) of Boron Steels –...

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