blanking and stamping of sheet materials · – hot stamping (press hardening) of boron steels –...
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Sheet Forming Group © Copyright Engineering Research Center for Net Shape Manufacturing, 2013
CPF
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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
Sheet Forming Group © Copyright Engineering Research Center for Net Shape Manufacturing, 2013
CPF
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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
Sheet Forming Group © Copyright Engineering Research Center for Net Shape Manufacturing, 2013
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.
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CPF Material Properties / Flow Stress
Tensile Test (uniaxial)
Ref: Nasser et al 2010
0.1
5
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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
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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
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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
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CPF
Shorter
Perimeter
Higher BHF before fracture
Cup Draw Test
Lubrication performance:
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Friction / Lubrication
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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
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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)
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CPF
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Servo-Hydraulic Cushion
(Courtesy-Aida)
During Down Stroke, Cushion Pressure Generates Power
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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.
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CPF
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U-CHANNEL DRAWING & U BENDING
DIE
BLANK
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CPF
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STRETCH FLANGING
DIE
BLANK
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CPF
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SHRINK FLANGING
DIE
BLANK
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CPF
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CURVED U CHANNEL FORMING
BLANK
DIE
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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)
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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
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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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Sheet Forming Group © Copyright Engineering Research Center for Net Shape Manufacturing, 2013
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
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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
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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
ph +1-614-292-5063
Please visit www.ercnsm.org
and www.cpforming.org
for detailed information
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