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By Dr. Eren Billur, Post-doctoral Researcher
andDr. Taylan Altan, Director and Professor
Presented at ESI Hot Forming Die Engineering Seminar
October 15th, 2013
Center for Precision Forming (CPF)
www.cpforming.org / www.ercnsm.org © Copyright Center for Precision Forming (CPF). All Rights Reserved.
Introduction to Hot Stamping and Trends
Center for Precision Forming - CPF
InterlakenTechnology Corporation
IMRA
2
CPF is supported by NSF and 16 member
companies, interested in metal forming.
CPF – Current Projects
• Material Characterization
• Friction / Lubrication
• Process Simulation / Forming Al & AHSS
• Die Wear in Forming AHSS
• Edge Quality in Blanking / Shearing
• Hot Stamping of UHSS
• Servo Drive Presses and Hydraulic Cushions3
Sponsors & Partners of Hot Stamping Research
4
TSGTooling Systems
Group
InterlakenTechnology Corporation
IMRA
5
Crashworthiness
Crumple Zone Crumple ZonePassenger Zone
Images from: media.Daimler.com
6
Crashworthiness
Passenger Zone Crumple Zone
Absorbing EnergyHigh Strength + Elongation
Intrusion ResistanceUltra High Strength
Ref: Hilfrich 2008.
A-pillars
B-pillars
Roof rail
Door beams
Summary of Hot Stamping
70 200 400 600 800 1000 1200 1400 1600 1800 20000
10
20
30
40
50
60
70
Ultimate Tensile Strength (MPa)
Tot
al E
long
atio
n (%
) Aust.SS
TRIP
TWIPIF
MildBH
CMn
MART
L-IPMild Steels
Conventional High Strength Steels
Advanced High Strength Steels
2nd Generation AHSS
Aluminum Alloys
AlAl
(hs)
Higher Press Forces
Bet
ter
For
mab
ility
Summary of Hot Stamping
80 25 50 75 100 125 150 175 200 225 250
0
10
20
30
40
50
60
70
Specific Strength (MPa/(kg/m3))
Tot
al E
long
atio
n (%
) Aust.SS
TWIPIF
MildBH
CMn
MART
L-IPMild Steels
Conventional High Strength Steels
Advanced High Strength Steels
2nd Generation AHSS
Aluminum Alloys
AlAl
(hs)
Lightweight Potential for Intrusion Resistance
Higher Springback
Summary of Hot Stamping
0 200 400 600 800 1000 1200 1400 1600 1800 20000
10
20
30
40
50
60
70
Ultimate Tensile Strength (MPa)
Tota
l Elo
ngat
ion
(%) Aust.
SS
TRIP
TWIPIF
MildBH
CMn
MART
1
2
Mn-B Alloyed steel (as delivered)
Ferrite & Pearlite
Heated >950 � CAustenite
QuenchedMartensite
3-5 min.sin Furnace
Quenched in the die >27 � C/s
Indirect Process:
Direct Process:
9
10
Hot Stamping - Trends
Mass % of hot stamped steel in BIW
Volvo V40
20%
2003 2006 2012 2014
VolvoXC90
7%
Volvo XC90 44%
VW Passat19%
Audi A3
26%VW Golf VII
28%
≈
1984
SAAB 9000
Ref: Lund 2009, Holzkamp 2011, Lindh 2011, Bielz 2012, Mattsson 2012, VW Media Services.
550
500
450
400
350
300
250
200
150
100
500
1987 1997 2007 ’08 ’09 ’10 ’11 ’12 ’13Year 11
Hot Stamping - TrendsParts per year (in millions)
3 million per year (1987)
8 million per year (1997)
95 million per year (2007)
450 million per year (2013)
210+ lines around the world
+55 planned
4 Parts/ Vehicle
6 Parts/ Vehicle
8-10 Parts/
Vehicle
>20 Parts/
Vehicle
Ref: Oldenburg 2010, Hund 2011.
Hot Stamping - Trends
12
Passenger Zone
Deformation Zone
(b) Side view after crash
(a) Front view before crash
Ref: Macek 2006, Image from: IIHS.
Hot Stamping - Trends
13
Tailor Rolled Blanks Tailored Hot Stamping
Tailor Welded Blanks
HSLA 340(50 ksi)
22MnB51500 MPa(215 ksi)
Ref: Rehse 2006, Hilfrich 2008, Lee 2012, Images from: IIHS, VW Media Services.
Hot Stamping - Trends
14
550 � C 20 � C
Tailored Heating (Austenitizing)
Tailored Quenching Post Tempering
Ref: Breidenbach 2009, Hedegärd 2011, Süß 2011, Steinhoff 2013. Image from: IIHS.
Hot Stamping - Trends
15
100
200
300
400
500
600
700
800
900T
empe
ratu
re ( C
)
Time to cool (s)Cooling Rate ( � C/s) Hardness (HV)
8100475
2730474
4020417
8010278
1336
232
11430.7163
40000.2150
2663
182
Ms
Mf
A+M
A+F
A+P
A+B
16
Finite Element Simulation of Hot Stamping
Our simulations aim to predict the final properties of hot stamped components:
1) Presence of defects: cracks, wrinkles or local necking,
2) Hardness distribution (both in uniform and in tailored parts),
3) Cooling channel analysis,
4) Distortion of the final part.
17
Microstructure Evolution
Mechanical Field Thermal Field
Fluid MechanicsHeat transfer to the coolant medium.
- Thermal material properties,- Latent heat due tophase transformation.
Microstructuredepends on
temperature.
- Mechanical materialproperties,- Volume change due to phase transformation.
Phase transformationdepends on stress and strain.
Heat generation due to plastic deformation.
Thermal expansion.
Ref: Åkerström 2006, Porzner 2012.
Finite Element Simulation of Hot Stamping
18
Gravity
Mechanical
Holding
Thermal + Mechanical
Forming
Thermal + Mechanical
Die Quenching
Thermal + Metallurgical
Air Quenching
Thermal + Metallurgical
Springback
Mechanical
Only needed in tailored parts
Finite Element Simulation of Hot Stamping
Part stamped at the participating company
19
Predicting Defects
Crack prediction in a Side Member Reinforcement
Colors other than gray:Thinning >20%.
20Heated Dies (Ti = 450 � C) Cooled Dies (Ti = 20 � C)
Blank (Ti = 850 � C)
Die Segment 1 Die Segment 2 Die Segment 3
Predicting Defects
21
Predicting Defects
Crack
Non-symmetric draw-in
Wrinkles in the soft area
With one-piece blankholder With two-piece blankholder
No wrinkles or cracks
15 kN 5 kN20 kN
Crack / wrinkle prediction in a tailored part
22
Hardness Distribution
Martensite phase fraction
Min = 0.00Max = 1.00
0.140.00
1.000.850.710.570.420.28
4 seconds die quenching 10 seconds die quenching
Die Quenching Optimization
0 10 20 30 40 50 60 70 800
20
40
60
80
100
Time (s)
Max
imum
Aus
teni
te (
%)
Hardness Distribution
Air Quenching Stage
0 200 400 600 800 10000
20
40
60
80
100
120
140
Temperature (C)
Heat Transfer Coefficient (W/m2C)
Convection
Radiation
Ref: Shapiro 2009.23
24
Hardness Distribution
Results
Hardened zone:485 – 515 HV1500 – 1590 MPa(~220 – 230 ksi)
Soft zone:310 – 330 HV920 – 1020 MPa(~135 – 150 ksi)
Literature:[George 2011] , 400°C dies = 790-840 MPa [Feuser 2011], 450°C dies = ~850 MPa
25
Cooling Channel Analysis
1.3 mm 22MnB5 “roof rail” Mass produced for a European car.
Cooling channel performance
26
Cooling Channel Analysis
Cooling channel performance – tailored part
1.2 mm 22MnB5 “B-pillar”
0 20 40 60 80 100 120 140 1600
50
100
150
200
250
300
Time (s)
Tem
pera
ture
( C
)
Max219 � C
Min20 � C
1 2 3 4 5 6 7 8 9 101580
1585
1590
1595
1600
1605
Part # (Cycle)
Max
imum
UT
S (
MP
a)
900
905
910
915
920
925
Min
imum
UT
S (
MP
a)
921.4 MPa
903.8 MPa
1589.4 MPa
1590.3 MPa
austenitisation
200 400 600 800 1000 1200 temperature
martensitic transformation
strain
0
-0.005
0.01
0.005
0.015
+Interstitial dissolved carbon
+ carbon, tetragonal distorted grid
+Initial,
undistorted grid
27
Distortion Analysis
Ref: Porzner 2012.
Material 1 Material 2
Ongoing work: Distortion in Tailored Parts
28
Summary and Conclusions
Several case studies were used to develop, calibrate and validate material models, conversion factors and methods to predict:
1) Defects (cracks, wrinkles, local necks),2) Vickers hardness, yield and ultimate tensile strengths,3) Cooling channel / heating cartridge performance,4) Distortion in a non-uniform part.
What is next?
29Ref: Lanzerath 2011, Vietoris 2011, Ferkel 2012, Lee 2012.
0 5 10 15 200
500
1000
1500
2000
Eng
inee
ring
Str
ess
(MP
a)
Engineering Strain (%)0 5 10 15 20
0
500
1000
1500
2000
Eng
inee
ring
Str
ess
(MP
a)
Engineering Strain (%)
High Strength (USIBOR 2000, MBW1900, HPF 2000)
22MnB5 (USIBOR 1500, MBW1500, HPF1470)
High Elongation (DUCTIBOR 500, MBW500)
1) New materials with even higher strength: More lightweight potential and increased productivity.
2) New coatings: better corrosion properties and friction conditions.
3) New heating, forming and quenching methods to improve productivity.
Competition: DP, TRIP, TWIP, and 3gAHS Steels with high YS and UTS.
Deliverables / Hot Stamping
As of September 2013:
- 15 CPF Reports (Literature review and FE simulations), (5 in the last 6 months) [confidential to members],
- 6 Stamping Journal R&D Updates (+1 more in progress),
- 6 Conference Proceedings (+1 more submitted),
- 1 Book Chapter in “Sheet Metal Forming: Vol 2: Processes and Applications”, (see next slide),
- And a new “Hot Stamping” book in progress! 30
Questions / Comments?
For more information , please contact:
Dr. Eren Billur ([email protected]), Ph 614-292-1785
Dr. Taylan Altan ([email protected]), Ph-614-292-5063
Center for Precision Forming –CPF (www.cpforming.org)
339 Baker Systems,1971 Neil Ave,
Columbus, OH-43210
Non-proprietary information can be found at web sites:
www.cpforming.org
www.ercnsm.org
References can be sent upon request.31
