By

Dr. Eren Billur, Post-doctoral Researcher

and

Dr. 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 Cushions 3

Sponsors & Partners of Hot Stamping Research

4

TSGTooling

Systems

Group

InterlakenTechnology Corporation

IMRA

5

Crashworthiness

Crumple Zone Crumple Zone Passenger Zone

Images from: media.Daimler.com

6

Crashworthiness

Passenger Zone Crumple Zone

Absorbing Energy

High Strength + Elongation Intrusion Resistance

Ultra High Strength

Ref: Hilfrich 2008.

A-pillars

B-pillars

Roof rail

Door beams

Summary of Hot Stamping

7 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.

SS

TRIP

TWIPIF

Mild

BH

CMn

MART

L-IPMild Steels

Conventional High

Strength Steels

Advanced High

Strength Steels

2nd Generation

AHSS

Aluminum Alloys

Al

Al(hs)

Higher Press Forces

Bett

er

Fo

rma

bili

ty

Summary of Hot Stamping

8 0 25 50 75 100 125 150 175 200 225 250

0

10

20

30

40

50

60

70

Specific Strength (MPa/(kg/m3))

Tota

l E

longation

(%) Aust.

SSTWIP

IF

Mild

BH

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 E

longation

(%) Aust.

SS

TRIP

TWIPIF

Mild

BH

CMn

MART

1

2

Mn-B Alloyed steel

(as delivered)

Ferrite & Pearlite

Heated >950 C

Austenite

Quenched

Martensite

3-5 min.s

in 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

Volvo

XC90

7%

Volvo

XC90

44%

VW

Passat

19%

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 - Trends

Parts 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)

22MnB5

1500 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

em

pera

ture

(C

)

Time to cool (s)

Cooling Rate ( C/s)

Hardness (HV)

8

100

475

27

30

474

40

20

417

80

10

278

133

6

232

1143

0.7

163

4000

0.2

150

266

3

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 Mechanics

Heat transfer to the

coolant medium.

- Thermal material

properties,

- Latent heat due to

phase

transformation.

Microstructure

depends on

temperature.

- Mechanical material

properties,

- Volume change due

to phase

transformation.

Phase

transformation

depends 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%.

20 Heated 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 = 0.00

Max = 1.00

0.14

0.00

1.00

0.85

0.71

0.57

0.42

0.28

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)

Maxim

um

Auste

nite (

%)

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 HV

1500 – 1590 MPa

(~220 – 230 ksi) Soft zone:

310 – 330 HV

920 – 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

)

Max

219 C

Min

20 C

1 2 3 4 5 6 7 8 9 101580

1585

1590

1595

1600

1605

Part # (Cycle)

Maxim

um

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?

29

Ref: Lanzerath 2011, Vietoris 2011, Ferkel 2012, Lee 2012.

0 5 10 15 200

500

1000

1500

2000

Engin

eering S

tress (

MP

a)

Engineering Strain (%)

0 5 10 15 200

500

1000

1500

2000

Engin

eering S

tress (

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 (billur.1@osu.edu), Ph 614-292-1785

Dr. Taylan Altan (altan.1@osu.edu), 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