19 the effects of ahss shear edge condition edge fracture
-
Upload
nakul-surana -
Category
Documents
-
view
204 -
download
4
Transcript of 19 the effects of ahss shear edge condition edge fracture
THE EFFECTS OF AHSS SHEAR EDGE CONDITION ON EDGE THE EFFECTS OF AHSS SHEAR EDGE CONDITION ON EDGE THE EFFECTS OF AHSS SHEAR EDGE CONDITION ON EDGE THE EFFECTS OF AHSS SHEAR EDGE CONDITION ON EDGE
FRACTUREFRACTUREFRACTUREFRACTURE
w w w . a u t o s t e e l . o r g
FRACTUREFRACTUREFRACTUREFRACTURE
Mike ShihMike ShihMike ShihMike Shih
Constantin Chiriac, Ming F. Shi
United States Steel Corporation
Automotive Center
Edge Fracture
Poor Shearing Edge Condition ?
w w w . a u t o s t e e l . o r g
• Edge Fracture in Stamping
• Conventional FLD fails to predict
Outline
• Background
• Laboratory Shearing Test
– Computer Control Hole Punch/Shear Process
• Evaluation of Punch/Shear Force
• Validation Edge Fracture Test
w w w . a u t o s t e e l . o r g
• Validation Edge Fracture Test
– Hole Expansion Test
• Evaluation of Shear Edge Condition
• Conclusions
Shear Rake angle Θ3
Front View
Straight Edge Shearing ( Blanking die , Trimming die )
Background
Shear Blade
Clearance
Sheet Metal
Blade Rake angle Θ1
Back Cut angle Θ2
(clearance angle)
Die Θ2
Blank Holder
w w w . a u t o s t e e l . o r g
Hole Punching ( Hole piercing die)
Die
Clearance
Punch
Blank Holder
Sheet Metal
Θ1 = Θ3
Blank Holder
Clearance
Punch
Bevel Shear
θ
Clearance
Specimen holding fixture
Die
Laboratory Shearing TestComputer control hole punch/shear process
• Computer control
• Bevel angle
• Die clearance
• Shear speed
• Shear load
w w w . a u t o s t e e l . o r g
Die Spring
Punch Pd
Dd
Punch
Die
Sheet steel
Holder
Tθ Y
X
Pd
tanθYX =
H
H=Pd X tan Θ
(1)
TY
X
cosθFFN ×=
θ
sinθFFf ×=
F
(2)
Schematic of Bevel Shear
w w w . a u t o s t e e l . o r g
Shearing Test Conditions:
• Bevel Shear Angle: 0, 3, 6, 9, 12, 18, 24 degrees
• Die Clearance: 5, 10, 15, 20, 25, 30 % of test steel thickness
• Low speed
H: height for each bevel angle
Punch force F ~ X ~ 1/ tan ΘΘΘΘ
tanθYX
F: Punch ForceSlug
Y: Punch Tip Penetration
When Y-T=H : penetration near completed
MaterialThickness Yield Tensile Total n
(mm) Strength (MPa) Strength (MPa) Elong. (%) Value
DP780 1 511 876 16.9 0.118
MECHANICAL PROPERTIES OF TESTED STEELS
w w w . a u t o s t e e l . o r g
DP780 1 511 876 16.9 0.118
DP980 1.2 573 1003 15.1 0.106
GradeThickness
[mm]
Punch diameter
[mm]
Die diameter
[mm]Clearance [%]
DP780 1.0 10.0 10.1 5
DP780 1.0 10.0 10.2 10
DP780 1.0 10.0 10.3 15
DP780 1.0 10.0 10.4 20
DP780 1.0 10.0 10.5 25
Hole Punch/Shear Conditions
w w w . a u t o s t e e l . o r g
DP780 1.0 10.0 10.5 25
DP780 1.0 10.0 10.6 30
DP980 1.2 10.0 10.2 8
DP980 1.2 10.0 10.3 13
DP980 1.2 10.0 10.4 17
DP980 1.2 10.0 10.5 21
punchdie DtClD +×= 100/2
Transverse Shearing Longitudinal Shearing
Hole Shearing Orientations
w w w . a u t o s t e e l . o r g
Material Rolling Direction
RR
Punch Load vs. Shear Angle
(DP780 1mm, transverse, die clearance 5%)
500
10001500
20002500
30003500
40004500
5000P
ea
k L
oa
d (
lbf)
5
10
15
20
25
30
35
40
45
Ra
tio
Peak 1Peak 2RatioRatio = 1/ tan Θ
Evaluation of Punch / Shear Force
Group 1 Group 2
Over 55% load reduction
Conventional Empirical
formula :
LTUTS0.7F ×××=
w w w . a u t o s t e e l . o r g
0500
0 3 6 9 12 18 24
Shear Angle (degree)
0
5
0
500
1000
1500
2000
13 13.5 14 14.5 15 15.5 16 16.5 17
Lo
ad
Time
Peak 1 Peak 2
0
500
1000
1500
2000
13 13.5 14 14.5 15 15.5 16
Load
Time
Peak 1
Die Spring Force
0
500
1000
1500
2000
13 13.5 14 14.5 15 15.5 16 16.5 17
Loa
d
Time
9P-C5
500
1000
1500
200024P-C5
Lo
ad (
lbf)
Increase Shear Angle
From 9 to 24 degree
Reduce Peak 1
increaseT∆
Peak 1
Peak 2
20009P-C30
Increase Die
Clearance
w w w . a u t o s t e e l . o r g
013 14 15 16 17 18 19 20
Time
0
500
1000
1500
13 13.5 14 14.5 15 15.5 16 16.5 17
Load (
lbf)
Time
Clearance
Reduce Peak 2
Inc. Peak 1
Comparison of Punch Penetration at
Load Peak 1 and Peak 2
4
5
6
Pe
ne
tra
tio
n (
mm
) Y1Y2H
Group 2
Punch Penetration
w w w . a u t o s t e e l . o r g
0
1
2
3
0 3 6 9 12 18 24
Shear Angle (Degree)
Pe
ne
tra
tio
n (
mm
)
Group 1Group 2
Top View
Bottom View
Curvature
Slug
Photograph of Punch/Shear Samples
3 degrees
Peak 1
6 degrees
Peak 118 degrees
Peak 2
w w w . a u t o s t e e l . o r g
Bottom View
3 degrees
Peak 16 degrees
Peak 118 degrees
Peak 2
Large
Rollover
Faster shearing
Slower shearing
Group 1 Group 2
Punch Load vs. Die Clearance
( DP780 1 mm, Transverse Shearing Direction )
4000
5000
6000
Pe
ak
Lo
ad
(L
bf)
0
3
6
9
12
18
24
Punch Force – DP780 1mm
Over 50 % load reduction
w w w . a u t o s t e e l . o r g
0
1000
2000
3000
5 10 15 20 25 30
Die Clearance (%)
Pe
ak
Lo
ad
(L
bf)
Over 50 % load reduction
Effects of Hole Shearing Orientations
1500
2000
2500
3000
Peak L
oad
(L
bf)
3-Trans
3-Long
6-Trans
6-Long
9-Trans
9-Long
Punch Force – DP780 1mm
Difference is larger at 3 degrees
w w w . a u t o s t e e l . o r g
0
500
1000
1500
10 15 20
Die Clearance (%)
Peak L
oad
(L
bf)
9-Long
Punch Load vs. Die Clearance
(DP980 1.2 mm, Longitudinal and Transverse)
4000
5000
6000
7000
Pe
ak
Lo
ad
(L
bf)
0
3-L
3-T
6-L
6-T
9-L
9-T
Punch Force – DP980 1.2 mm
w w w . a u t o s t e e l . o r g
0
1000
2000
3000
4000
8% 13% 17% 21%
Die Clearance
Pe
ak
Lo
ad
(L
bf)
9-T
Validation Edge Fracture Test Hole Expansion Test
w w w . a u t o s t e e l . o r g
• Hole expansion test
• Specimen orientation : Burr Up
• Conical punch
• 1 inch/minTinus-Olsen formability machine
DP780 , 1mm, Transverse
40%
50%
60%
Ho
le E
xp
an
sio
n R
ati
o
flat3 degree6 degree9 degree12 degree18 degree24 degree
Effects of Bevel Shear Angle and Die clearance
Over 51 % improvement
3 or 9 degrees ?
w w w . a u t o s t e e l . o r g
0%
10%
20%
30%
5% 10% 15% 20% 25% 30%
Die Clearance
Ho
le E
xp
an
sio
n R
ati
o
Dp780, 1mm
40%
50%
60%
Ho
le E
xp
an
sio
n R
ati
o
flat 3 degree-L
3 degree-T 6 degree-L
6 degree-T 9 degree-L
9 degree-T
Effects of Material Shearing Orientations
3 or 6 degrees
15% < CL < 20%
w w w . a u t o s t e e l . o r g
0%
10%
20%
30%
10% 15% 20%
Die Clearance
Ho
le E
xp
an
sio
n R
ati
o
DP980, 1.2 mm
25%
30%
35%
40%
45%
50%
Ho
le E
xp
an
sio
n R
ati
o
flat
980-3-L
980-3-T
980-6-L
980-6-T
9 degree-L
9 degree-T
Effects of Material Shearing Orientations
Over 60 % improvement3, 6 and 9
w w w . a u t o s t e e l . o r g
0%
5%
10%
15%
20%
25%
8% 13% 17% 21%
Die Clearance
Ho
le E
xp
an
sio
n R
ati
o
Evaluation of Shear Edge Condition
Rollover depth
Burnish surface
Fracture angle
Penetration depth
w w w . a u t o s t e e l . o r g
Burr height
Rough fracture surface
Fracture depth
Rough fracture surface Flat Punch
Smooth fracture surfaceAngle Punch
w w w . a u t o s t e e l . o r g
No Visible Burr With Visible Burr
50 X 50 X
w w w . a u t o s t e e l . o r g
Die Clearance < = 20 % Die Clearance >=25 %
~ 0.138 mm~ 0.006 mm
Material Rolling Direction
Transverse Shearing
R
Longitudinal Shearing
R
HET Fracture Locations / Surface
w w w . a u t o s t e e l . o r g
R
HET fracture locations
along rolling direction
R
1
2
3
R1
2
3
Longitudinal Shearing (9 degrees, 10% CL)
No Fracture
Shear direction
Shear direction
Fracture
w w w . a u t o s t e e l . o r g
R 1
3
HET fracture locations
2
Location 1 3D FormationLocation 2
No Fracture
Shear direction
Location 3
Large Plastic
Deformation
Transverse Shearing
(12 degrees, 15% CL)
Location 1
3D Formation
Fracture location
at 1 or 3
Fracture
w w w . a u t o s t e e l . o r g
R
1
2
3
Location 3
Large Rollover
On trailing edge of the bevel shear punch
(Bevel Shear Angle > 9 degrees)
Tensile mixed type failure
Fracture
12 degree, 15 % clearance- Loc. 3
Large rollover
Location 3
Cause for relative larger load
peak 2 - tensile /shear mixed
type failure
w w w . a u t o s t e e l . o r g
18 degree, 15 % clearance- Loc. 1
Back Cut
Negative rollover
0
Burnish Depth
Burnish Depth vs. Die clearance
(Dp780, Location 1, Transverse)
25
30
35
Bu
rnis
h D
ep
th
(% o
f m
ate
rial th
ickn
ess)
F-B
3T-B
6T-B
9T-B
12T-B
18T-B
w w w . a u t o s t e e l . o r g
0
5
10
15
20
10 15 20
Die Clearance (%)
Bu
rnis
h D
ep
th
(% o
f m
ate
rial th
ickn
ess)
24T-B
Rollover Depth
Rollover Depth vs. Die Clearance
(DP780, Location 1, Transverse)
15
20
25
Ro
llo
ve
r D
ep
th
(% o
f T
hic
kn
es
s)
F-Roll
3T-R
6T-R
9T-R
12T-R
18T-R
w w w . a u t o s t e e l . o r g
-5
0
5
10
10 15 20
Die Clearance (%)
Ro
llo
ve
r D
ep
th
(% o
f T
hic
kn
es
s)
18T-R
24T-R
� Beveling shearing/piercing process has been developed at a lab base
hydraulic press and has been successfully used for piercing holes for
AHSS.
� The maximum shearing force can be significantly reduced more than
50% when a beveling angle is used during shearing. The shearing
force depends also upon the die clearance during shearing.
Conclusions
w w w . a u t o s t e e l . o r g
� The optimal shearing condition results in more than 60% improvement
in the hole expansion ratio when compared to conventional flat head
punching process.
� The optimized shearing condition for piercing and shearing AHSS is
the combination of a beveling angle between 3 and 6 degrees and a
17% die clearance and the shearing direction parallel to the material
rolling direction.
w w w . a u t o s t e e l . o r g