GDIS2018

A New Hybrid Bead with Post-stretching

Method to Effectively Control Spring-back for

Advanced High-Strength Steel

Yu-Wei Wang, AK Steel Corporation

Auto/Steel Partnership

#GDIS | #SteelMatters 3

Name Company

K. Schmid GM

D. J. Zhou FCA US LLC

F. Ren Ford Motor Company

C. Pu AK Steel

Y.Wang AK Steel

M. Huang ArcelorMittal USA

Name Company

E. Liasi Ford Motor Company

C. Chiriac Ford Motor Company

Y. Shen Ford Motor Company

C. Roman GM

W. Sun Nucor Corporation

J. Catterall A/SP

Project Members and Lead: V. Jia, C. Pu, W. Wu, J. Makrygiannis, Y. Wang, AK Steel

A/SP Team Leads: Changqing Du, FCA; Gene Hsiung, GM

A/SP Team Manager: Eric McCarty JPC Mentor - Rick Johnson, FCA

AHSS Stamping Team Members

#GDIS | #SteelMatters 4

Problem: Spring-back in Manufacturing

• How to Control it? Stretch it!

• How to Stretch it? Clamp it!

− Hybrid beads

#GDIS | #SteelMatters 5

Solution: Post-stretching

• Phase 1 Lab-scaled Hybrid Bead Development

− U-channel Lab-scaled Hybrid Bead Die Concepts

− Hybrid Bead Design Based on Finite Element Simulations

− Test Die, Results and Analysis

− Advantages and Conclusions

• Phase 2 (Hat Section Rail Die): Production-Scale Application Study

• Phase 3 High Volume Production Robustness Study

#GDIS | #SteelMatters 6

• A U-channel die was designed and manufactured to implement the Clamp-Stretch concept.

• A clamp hybrid bead was developed and applied to clamp the blank.

• Multiple conceptual inserts were designed.

Inserts

Stop Block

Wear Plate

U-channel Lab Scaled Die Design

#GDIS | #SteelMatters 7

Solution: Post-stretching

• Phase 1 Lab-scaled Hybrid Bead Development

− U-channel Lab Scaled Hybrid Bead Die concepts

− Hybrid Bead Design Based on Finite Element Simulations

− Test Die, Results and Analysis

− Advantages and Conclusions

• Phase 2 (Hat Section Rail Die): Production-Scale Application Study

• Phase 3 High volume production robustness study

#GDIS | #SteelMatters 8

Hybrid Bead Design with FE Simulation

Ideal Fully-locked

Hybrid Beads with 3 Cavities

Hybrid Beads with 5 Cavities

Waved Hybrid Bead with Cavities

Conventional Stinger Beads without Cavity

15 mm

A

B

C

D

E

#GDIS | #SteelMatters 9

Hybrid Bead Design for Effective Stretch

tretch)Simulation X-axis: Forming Depth (mm) with Bead Engaged

Y-axis: Major Stress (MPa, Abs)

A

B

C

D

E

Ideal Fully-lock

3 Stingers Bead with Cavity

5 Stingers Bead with Cavity

Waved Bead with Cavity

Conventional Stinger Bead without Cavity

16mm

Stress Difference

Evolution Contour

Forming with

Bead Engagement Bead Area

Major Stress Histories, Wall

Inner and Outer Surfaces

#GDIS | #SteelMatters 10

Hybrid Bead Design with FE Simulation

• Spring-back behavior was simulated

and winner is … Design B:

Hybrid Beads with 3 Cavities!

with least Springback

Before Spring-back Ideal Fully-locked

Hybrid Beads with 5 Cavities

Waved Bead with Cavities

Conventional Stinger Bead without Cavity

Hybrid Beads with 3 Cavities! A

B

C

D

E

#GDIS | #SteelMatters 11

Preferred Hybrid Bead Design

• Synergistic effect of both wave-shaped bead forming and teeth penetration.

• Material Saving: 78%, with reduced risk of fracture in bead forming vs. traditional draw bead.

• Lower risk of fracture at bead

Blank Needed to Form

Conventional Bead Major Stress (Abs)

Totally Bead Length: >35 mm

Blank Needed to Form

Hybrid Bead

Hybrid Beads with 3 Cavities

7.5 mm

#GDIS | #SteelMatters 12

Solution: Post-stretching

• Phase 1 Lab-scaled Hybrid Bead Development

− U-channel Lab Scaled Hybrid Bead Die concepts

− Hybrid Bead Design Based on Finite Element Simulations

− Test Die, Results and Analysis

− Advantages and Conclusions

• Phase 2 (Hat Section Rail Die): Production-Scale Application Study

• Phase 3 High volume production robustness study

#GDIS | #SteelMatters 13

Punch

Upper Binder / Die

Inner Binder

(b)

(c)

U-channel Die

• The die was installed in a Servo Press to stamp U-channel parts.

• The parts were successfully stamped as the FEA predicted.

Nitrogen Spring Cylinders

Upper Binder / Die

Outer Binder

Punch

Upper Binder / Die

Inner Binder

(a) (b)

(c)

(d)

Punch

Blank: During Drawing

Formed Part

Punch

Inner Binder

Inner BinderNitrogen Spring Cylinders

Upper Binder / Die

Outer Binder

(a)

#GDIS | #SteelMatters 14

Test Results: Great Springback Control

Top view Front view

Part Geometry without

Post-stretching (top) Part Geometry with

Post-stretching (bottom) vs.

#GDIS | #SteelMatters 15

U-channel Die: Test Results

#GDIS | #SteelMatters 16

U-channel Die Test Results

• Excellent spring-back control was achieved with successful clamping

• DP980, CP1180, 3rd Gen. 1000 MPa, 1200MPa

0 mm

5 mm

6 mm

7-10 mm

Bottom

Surface Top

Surface

Hybrid Bead: No Material Sliding

Top Surface

Bottom Surface

5 mm 5 mm

1.2 mm

Effect of Post-stretching Amount

#GDIS | #SteelMatters 17

Post Stretch / Clamping Force vs. Springback • Achieved excellent spring-back control

• Minimal tonnage requirement - significantly reduced the clamping force to

0.1T/mm for DP980 (50%), 0.175T/mm for CP1180 (12.5%)

• Post-stretching amount to 7 mm.

0.2

Po

st-

str

etc

hin

g A

mo

un

t (m

m)

0.09 0.1 0.15

7

6

5

10 Necking

No Sliding Marginal

Sliding

8 10

4

7

8.5

5.5

Sidewall Curl Angle (°)

Good Spring-back Control

Moderate Spring-back Control

with Visible Sidewall Curl

No Sliding No Sliding

Clamping Force (T/mm)

0.15 0.175 0.2

7

6

8.3 Necking 8

10

6

7

9

Sidewall Curl Angle (°)

Good Spring-back Control

Moderate Spring-back Control

with Visible Sidewall Curl

8

CP1180 1.2 mm DP980 1.2 mm

No Sliding Marginal Sliding No Sliding

#GDIS | #SteelMatters 18

• Significantly reduced the clamping force to 0.13T/mm (3rd Gen. 1000 MPa), 0.24T/mm (3rd

Gen. 1200 MPa)

• Stretching amount 7 mm (3rd Gen. 1000 MPa), 8 mm (3rd Gen. 1200MPa).

8

9 8.5

6.5

7.5

4.5

5.5

3.5

8.5

6.5

7.5

4.5

5.5

3.5

0.15 0.12 0.13

7

6

5

10 Edge Crack

No Sliding Marginal Sliding

8

Sidewall Curl Angle (°)

Good Spring-back Control

Moderate Spring-back Control

with Visible Sidewall Curl

No Sliding

Clamping Force (T/mm)

0.23 0.24 0.25

10 Necking Sidewall Curl Angle (°)

Good Spring-back Control

Moderate Spring-back Control

with Visible Sidewall Curl

3rd Gen. 1000

7

6

No Sliding Marginal Sliding No Sliding

Post Stretch / Clamping Force vs. Springback

3rd Gen. 1200

Po

st-

str

etc

hin

g A

mo

un

t (m

m)

#GDIS | #SteelMatters 19

Hybrid Bead: Capable and Strong

Strong, Robust Hybrid Bead performance, Excellent performance of resistance to failure

.

#GDIS | #SteelMatters 20

Solution: Post-stretching

• Phase 1 Lab-scaled Hybrid Bead Development

− U-channel Lab Scaled Hybrid Bead Die concepts

− Hybrid Bead Design Based on Finite Element Simulations

− Test Die, Results and Analysis

− Advantages and Conclusions

• Phase 2 (Hat Section Rail Die): Production-Scale Application Study

• Phase 3 High volume production robustness study

#GDIS | #SteelMatters 21

Advantages and Conclusions

• Comprehensive Spring-back Control

− Excellent Synergistic Clamping Effect in Lab Trials.

• Material savings: 78% flange reduction

− For Shotgun Panel, 15% less of part blank.

• Lower risk of fracture at bead

− No bending over tight bead radius and related potential fracture.

#GDIS | #SteelMatters 22

Solution: Post-stretching

• Phase 1 Lab-scaled Hybrid Bead Development

− U-channel Lab Scaled Hybrid Bead Die concepts

− Hybrid Bead Design Based on Finite Element Simulations

− Test Die, Results and Analysis

− Advantages and Conclusions

• Phase 2 (Hat Section Rail Die): Production-Scale Application Study

• Phase 3 High volume production robustness study

#GDIS | #SteelMatters 23

• Hybrid Beads are being implemented on a production scale die at AutoDie LLC

Phase II: Production Scale Application

Lower master

die assembly

Upper master

die assembly

#GDIS | #SteelMatters 24

Solution: Post-stretching

• Phase 1 Lab-scaled Hybrid Bead Development

− U-channel Lab Scaled Hybrid Bead Die concepts

− Hybrid Bead Design Based on Finite Element Simulations

− Test Die, Results and Analysis

− Advantages and Conclusions

• Phase 2 (Hat Section Rail Die): Production-Scale Application Study

• Phase 3 High volume production robustness study

#GDIS | #SteelMatters 25

Phase 3 High Volume Production Robustness

study

s • Bead Profile Optimization

− Rounded corners and small ramps were added to reduce the stress

concentration

− New Profile Design: FEA is underway to assess bead designs

• Surface Treatment

− Laser Cladding of hard carbide powder to improve teeth durability

Synergy Additive Manufacturing LLC (SAM)

#GDIS | #SteelMatters 26

Improvement of Bead Robustness

• Rounded corners and small ramps were added to reduce the stress

concentration of the bead.

• Outstanding performance of clamping.

Hybrid Bead Original Design Hybrid Bead Improved Design

Blank Blank

Rounded Corners

#GDIS | #SteelMatters 27

For More Information

Yu-Wei Wang

AK Steel Corporation

313-317-1301

yu-wei.wang@aksteel.com