An Innovative Shearing Process for AHSS Edge Stretchability Improvements

8/17/2019 An Innovative Shearing Process for AHSS Edge Stretchability Improvements

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AN INNOVATIVE SHEARING PROCESS FOR AHSS EDGE STRETCHABILITY

IMPROVEMENTS

Mike Shih

United States Steel Corporation


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AHSS Edge Fracture

• AHSS Edge Fracture

• Conventional FLD fail to predict

Cause: – Material Property

– Die Condition

– Poor Sheared Edge Condition


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Introduction Optimized Bevel Shear Hole Piercing

Hole Expansion Test

Evaluation of the Sheared Edge

Developmental Straight Edge Shearing

Adjustable Shearing Device

Sheared Edge Tension Test

Sheared Edge Dome Test

Sheared Edge Limit Strain

Conclusions

Outline


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Shearing Processes

Hole Punching ( Hole piercing die)

Die

Clearance

Punch

Blank Holder

Sheet Metal

Blank Holder

Clearance

Punch

Bevel Shear

θ

Straight Edge Shearing ( Blanking die , Trimming die )

Shear Rake angle Q3

Front ViewUpper Blade

Clearance

Sheet Metal

Blade Rake Angle Q2

Back Cut Angle

(clearance angle)

Blank Holder

Q1Lower Blade

Introduction


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Blank Holder

Clearance

Punch

θ

6 degrees

Specimen holding fixture

Die spring

Die

Punch

Pd

Dd

Punch

Die

Sheet Steel

Holder

Optimized Bevel Shear Hole Piercing


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Punch Load vs. Die Clearance(DP980 1.2 mm, Longitudinal and Transverse)

0

1000

2000

3000

4000

5000

6000

7000

8% 13% 17% 21%

Die Clearance

P e a k

L o a d (

L b f )

03-L

3-T

6-L

6-T

9-L9-T

Over 50 load drop

Shear Load


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DP780 1mm

0%

10%

20%

30%

40%

50%

60%

10% 15% 20%

Die Clearance

H o l e E x p a n s i

o n

R a t i o

flat 3-L 3-T 6-L6-T 9-L 9-T

Hole Expansion Test



Hole Expansion Test - DP980

0%

10%

20%

30%

40%

50%

5% 7% 9% 11% 13% 15% 17% 19%

Die Clearance (%)

H o l e E x p a n s i o n R a t i o

DP980 1.2 mm

DP980 2 mm

Best Shearing Condition

6 degrees Bevel Shear



Optimized Shearing Condition- 6 Degrees, 15% DC, Longitudinal Shearing

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%

1Test Material

H o l e E x p a n s i o n

R a t i o

50XK-F

50XK-6L

Dp600-2mm-F

DP600-2mm-6L

Dp780-1mm-F

DP780-1mm-6L

TRIP780-1.6mm-F

TRIP780-1.6mm-6L

Dp980-2mm-F

Dp980-2mm-6L

F

F

F F F

50XK 1.4mm

DP780 (1mm)

Trip780 (1.6mm)

DP980 2mm

Optimized Shearing Condition

DP600 2mm40%

23%62%

25% 39%



Concept Punch

6 degrees 6 degrees 6 degrees 9 degrees

Optimized : 6L Concept 1 : 6-6 Concept 2 : 6C Concept 2 : 9C

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%

140.0%

50XK-

F

50XK-

6L

50XK-

6C

50XK-

9C

600-

1-F

600-

1-6L

600-

1-6C

600-

1-9C

600-

1-66

600-

1.6-F

600-

1.6-

6L

600-

1.6-

6C

600-

1.6-

9C

600-

2-F

600-

2-6L

600-

2-6C

600-

2-66

Punch Condition

H o l e

E x p a n s i o n R a t i o

50XK

DP600 1mm DP600 1.6 mm DP600 2 mm

6-6

F

F FF

6L

6L6L 6L

6-6



Evaluation of the Sheared Edge

(1) (2)

Burnish

Rollover

Optimized Bevel Shear - 15%

Fracture

(1) (2)

Rollover

Flat Head Punch - 15%

Burnish

Fracture

(1)(2)

Initial Contact

Point

Final Contact

Point

Section cut

Rolling

1/2 Burnish

200

220

240

260

280

300

320

340

360

0 100 200 300 400 500 600 700 800

Distance from SF[microns]

H V

Typical Optimized Conventional

Optimized

1/2 Fracture

200

220

240

260

280

300

320

340

360

380

0 100 200 300 400 500 600 700 800

Distance from SF[microns]

H V

Typical Optimized Conventional

Optimized

Microhardness profile of test DP780 , Chiriac, C. et al. 2011, MS&T 2011

Bevel

Shear

Rollover

(%)

Burnish

(%)

Fracture

(%)

HER

(%)

Side 1 12 21 68 53

Side 2 13 13 74

Flat

Head

Rollover

(%)

Burnish

(%)

Fracture

(%)

HER

(%)

Side 1 16 21 63 32

Side 2 16 21 63



Shear Rake AngleQ3

Front View

Developmental Straight Edge Shearing

Upper Blade

Die Clearance

Sheet Metal

Upper Blade Rake AngleQ2

Back Cut Angle(clearance angle)

Holding Pad

Lower Blade

Lower Blade Rake Angle Q1



Upper Blade

Lower Blade

Shear Rake Angle Q3

Adjustable Straight Edge Shearing Device



Q3 = 1 degree

Q3 = 2 degrees

Q3 = 3 degrees

Q3 = 4 degrees

Q3 = 5 degrees

Effect of the Shear Rake Angle

Curve

Q3



0

5

10

15

20

4 6 8 10 12 14 16 18

001

002003004

S h e a r L o

a d ( K N )

Displacement (mm)

4 degrees

1 degree

2 degrees

67% load drop

22% energy drop

3 degrees

78% load drop

19% energy drop

Shear Load Between Different Shear Rake AnglesQ3

Q3


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Transverse Shearing

Sheet Metal

Longitudinal Shearing

Sheet Metal

Specimen Shearing Direction


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600

700

800

900

1000

1100

1200

1300

1400

0 1 2 3 4 5 6

363-10%363-15%363-20%

S h e a r L o a d ( L b s )

Time (Sec)

1000

1050

1100

1150

1200

1250

1300

1350

1400

4 5 6 7 8 9

363-L363-T

S h e a r L o a d ( L b s )

Time (Sec)

Different Shearing DirectionDifferent Die Clearance

5.2% energy drop

15.8% energy drop

26.5% energy drop

Comparison of the Shear Load

321

θ,θ,θ : Shear Rake Angle 3θ: Lower Blade Rake Angle 1θ : Upper Blade Rake Angle 2θ


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Milled Edge

Sheared Edge

Sheared Edge Tension (SET) Test


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22

23

24

25

26

27

28

29

CV JIS 333 363 393 633 663 693 933 963 993

Shearing Condition

T

E ( % )

Conventional

ShearingJSTM

Milled

8% improvement

Total Elongation (TE) Between Different

Shearing Conditions


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Tensile failureLocalized

Necking

Fracture

initiation

Edge crack +

Tensile failure

Tensile failure +

Localized Necking

Type (4)

Fracture

As-sheared

edge

Fracture Fracture

Type (3) Type (2) Type (1)

As-sheared

edge

As-sheared

edge As-sheared

edge

Different Failure Modes in the SET test


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19

21

23

25

27

29

333 363 393 633 663 693 933 963 993

Shearing Conditions

T E

( % )

10%

15%

20%

12

Effects of Die Clearance

3

DP600, 1mm


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Edge Fracture3D Stretching

Half Specimen Dome

Burr Up Condition

Sheared Edge Dome Test


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25

30

35

40

45

50

333 363 393 633 663 693 933 963 993

Shearing Condition

D o m e H e i g h t ( m m )

10%

15%

20%

Comparison of the Dome Height

123 3


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0%

5%

10%

15%

20%

25%

30%

35%

40%

333 363 393 633 663 693 933 963 993

Shearing Condition

F r a c t u r e

S t r a i n

10%

15%

20%

Comparison of the Strain at Failure

12 23 3


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Sheared Edge Limit Strain (SELS)

o

f o

A

A Aq

1001

q

qSELS

Criterion

• The first through-thickness crack at the edge

• The onset of local necking

10

12

14

16

18

20

22

24

10 15 20

Die Clearance (%)

S h e a r e d E

d g e L i m i t S t r a i n ( % ) 333

363

DP980 1.2 mm

Best Shearing Conditions: 363, (333 or 663) with 15% die clearance

(Methodology: Wang, J. et al. 2008, International Conference on New Developments in Advanced High -Strength Sheet Steels)


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Conclusions

The experiments confirmed that the use of the optimal hole shearing condition can result in

significantly better edge stretchability for all AHSS.

A computer controlled adjustable straight edge shearing device was successfully developed

based on the findings from the beveled shear hole piercing process.

The maximum shearing force and applied energy can be significantly reduced when proper shear

variables are used during shearing.

The shearing force also depends upon the die clearance, and the larger die clearance tends to

the decrease the shear force.

The sheared edge tension test and dome test confirmed that the optimal setup of the rake

angles in the straight edge shearing process would result in a significant improvement of edge

stretchability for test AHSS.

The optimal shearing condition for AHSS is using the rake angle setup (3,6,3) with 15% die

clearance.


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An Innovative Shearing Process for AHSS Edge Stretchability Improvements

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