Transcript Worthington Progress I - Ohio State University

Current Applications of FE Simulation for
Blanking and Stamping of Sheet Materials
CPF
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
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OUTLINE
CPF
– 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
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Center for Precision Forming
(www.cpforming.org)
CPF
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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Introduction / Major Trends
CPF
• 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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Properties of Various Stamping Materials
70
Better Formability
Mild Steels
Total Elongation (%)
60
50
40
30
20
10
0
CPF
L-IP
Aust
.
IF
Mil
d BH
Al CM
Al
(hs)
n
Conventional High Strength
Steels
TWIP
Advanced High Strength Steels
SS Lightweight Potential*
TRIP
2nd Generation AHSS
Higher forces & springback*
Aluminum alloys
*
MART
0
200
400
600
800
1000 1200 1400
Ultimate Tensile Strength (MPa)
1600
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1800
2000
Steel
Al has
lightweight
modulus
compared
strength.
to steel comparison.
lower density (more
potential) and lower E(more
springback)
to steel with similar
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Material Properties / Flow Stress
Tensile Test (uniaxial)
CPF
0.1
5
Ref: Nasser et al 2010
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Material Properties / Flow Stress
CPF
Using real time measurements of pressure and dome height
and FE Analysis
Viscous Pressure Bulge Test (biaxial)
Ref: Nasser et al 2010
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CPF
Material Properties/Flow Stress
Bulge Test (biaxial)
0.4
9
1)
2)
Tensile test gives a very limited information,
Bulge test gives more reliable strain-stress data.
Ref: Nasser et al 2010
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Comparison of flow stress determined by
Tensile test and bulge test
True Stress (MPa)
1000
Uniform Strain
from Tensile
Test = 0.16
800
True Stress (ksi)
145
Tensile data with Power Law
(σ=Kεn)
116
600
Useful strain 87
from Bulge
Test = 0.49
400
58
200
Material, DP600, t0 =1 mm
0
0
0.1
CPF
0.2
0.3
True Strain
VP Bulge Test
29
Tensile Test
0.4
0.5
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Materials Tested with VPB Test at CPF
Steels and Stainless Steels
St 14
DP 780-CR
St 1403
DP 780-HY
AISI
Bare DP 980 Y-type X
1018
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
DQS-270F GA-Phosphate
BH 210
coated
DQS-270D GA-Phosphate
HSS
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
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CPF
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Formability / Fracture in Bulge Test
CPF
SS304 sheet material from eight different batches/coils
[10 samples per batch]
Highest formability  G , Most consistent  F
Lowest formability and inconsistent  H
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Dome Test (LDH) / Flow Stress
CPF
[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)
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Friction / Lubrication / Cup Draw Test
(CDT)
12 inch
CPF
Initial blank
6
inch
Cushion Pins
Deep drawn
cup
Schematic of CDT Tooling at CPF/EWI
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Friction / Lubrication
CPF
Cup Draw Test
Lubrication performance:
Shorter
Perimeter
Higher BHF before fracture
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CPF
Cup draw test results for Al
755
Blank holder force =16 ton
Flange Perimeter (mm)
750
745
Best lubricant
740
735
730
725
720
715
L1
L2
L3
L4
L5
L6
L7
Lubricant code
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.
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Friction / Lubrication / Temperatures
CPF
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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Ref: Kim et al 2009
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Forming in a Servo-Drive Press
CPF
The flexibility of slide motion in servo drive (or free motion) presses. [Miyoshi, 2004]
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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
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Potential Improvements in Forming with
Servo Drive
CPF
• 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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Forming of Al alloy in Servo Press
Die Design I (Thinning Distribution)
CPF
Max thinning :22.1%
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Forming AHSS in Servo Press
Die Design
CPF
CPF die set ( for 160 ton press/ detailed drawings are available)
Tool dimensions
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CPF
STRAIGHT FLANGING
BLANK
DIE
R7
451.6 mm
R4
598.4 mm
R5
56.6 mm
R6
41.6 mm
R7
46.6 mm
R8
51.6 mm
R8
R4
R3
R6
R3
R5
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The radii will be
modified, based on
results of FE simulations
with DP 980 and DP 780.
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U-CHANNEL DRAWING & U BENDING CPF
BLANK
DIE
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CPF
STRETCH FLANGING
DIE
BLANK
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CPF
SHRINK FLANGING
DIE
BLANK
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CPF
CURVED U CHANNEL FORMING
DIE
BLANK
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FE MODEL OF A DEEP DRAWN PART
CPF
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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Easy to Form
Hot Stamping (Press Hardening)
CPF
At ~950°C
Austenite
3-5 min.s
in
Furnace
Less force and
springback
Quenched
>27°C/s (~49°F/s)
Mn-B alloyed steel
(As delivered)
Ferrite-Pearlite
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Quenched
Martensite
Ref: Gutermuth 2011,
26
Tailored B-Pillar / Simulation
CPF
Effect of blank holder design
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Tailored B-Pillar with soft zone
CPF
UTS = 920-1020 MPa
Estimated UTS (MPa)
1600
1500
1400
1300
1200
1100
1000
900
Min =
Max =
UTS = 1500-1590 MPa
924
1591
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Blanking and Hole Flanging
Schematic of blanking
CPF
Schematic of hole
expansion (flanging)
dd
DIE
rd
dh
θ
dp
Blank Holder
fb
Punch
db
vp
fb=blankholder force
vp=punch velocity
dd=diameter of the die
θ=punch angle (conical)
db=diameter of blankholder rd=die radius
dh=diameter of pierced hole in the blank
dp=punch diameter (hemispherical)
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Blanking / Flanging
CPF
• 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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Parameters Affecting Blanked Edge Quality CPF
and Hole Flanging
• Punch/die clearance
• Blankholder pressure
• Punch tip geometry
• Punch velocity (continuous or intermittent
blanking/possible use of a servo-press)
during
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
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]
Single shear
Conical with flat tip
Conical
with
spherical tip
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Humped
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Improving Tool Life in Blanking
CPF
Experiments by [Högman 2004]
•
•
•
(a) Uniform clearance
Chipped after 40,000 strokes
(b) Larger clearance
Sheet material - Docol800 DP,
1mm thick.
Punch material – Vanadis 4, 60
HRC
Punch wear from experiments
correlate with punch stress
from FEA.
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
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CPF
Prediction of Necking / Tensile Test Simulations
Thinning progression
2
12
10
Thickness Strain ()
1.5
Load (kN)
8
6
4
Al 5182-O, t0 = 1.5 mm
Flow stress from bulge
test
2
0
1
0.5
Simulation
Experiment
0
0
2
4
6
8
Elongation (mm)
10
12
14
0
10
20
30
Time(sec)
40
50
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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Strain vs. stroke in cup drawing
CPF
ate
r
Material SS304
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Summary / Future Outlook
CPF
• 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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Questions/Comments
CPF
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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