study of sheet metal stamping processes

8/21/2019 Study of Sheet Metal Stamping Processes

1/93

Two-stage stamping of cold drawn magnesium

alloy cup having small bottom corner.6.

Multi-stage stamping of tailor square blank forincrease in wall thickness at bottom corner ofsquare cup.

5.

Multi-stage stamping of high strength steel wheeldisk having large inner corner thickness.

4.

Two-stage stamping of tailor circular blank forincrease in wall thickness of wheel disk.

3.

Multi-stage stamping of wheel disk having largeinner corner thickness by means of conical punch.

2.

Introduction.1.

ContentsChapter

A study of sheet metal stamping processes

of lightweight partsFebruary 2008 Tan Chin Joo


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Chapter 1 Introduction

FlatSmallthickness: lowstrength

Localthickening

Large thickness:

high strength

Stamping

Tailor rolled blank

Long welding lines &high material loss

Tailor welded blank One-dimensional distribution

Control of thickness distribution of stamped products forreduction in weight

Proposed method for reduction in weight

Small thickness blank

Welding lines

Lightweight


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Forming of lightweight material forreduction in weight of parts

Density : 1/4 of mild steel

Specific strength : 2 times of mild steel

Advantages

Low formability at room temperature

Formed at elevated temperature Heating apparatus is expensive and

complicated

Disadvantages

Magnesium alloy


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alloy cup having small bottom corner.

6.


5.


4.

Two-stage stamping of tailor circular blank for

increase in wall thickness at inner corner at innercorner of wheel disk.

3.


2.Introduction.1.

ContentsChapter


of lightweight parts


5/93

Chapter 2

Multi-stage stamping of wheel disk having largeinner corner thickness by means of conical punch

Steel Wheel

Welding

Roll forming

Bending, weldingMulti-stage stamping

Blanking

Disk forming Rim forming

Forming process of steel wheel


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Relationship between weight of wheel and fuel

consumption

Engine

Wheels

Drive shaft

Reduction in weight of wheel

Less fuel consumption

Wheels directly driven by engine


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Rim

Steel wheel

Local thickening at

Strength Fatigue life

Innercorner

Blank thickness

Disk

Target portion of wheel disk for local thickening

Hat portion

Drive shaft

Cracks in fatigue test

Rotating bending fatigue test

* K. Tanaka, K. Ishihara, H. Komatsu, Fatigue strength of car road wheels, SumitumoMetal, 39(4), p.325-336, 1987 (In Japanese).

T. Yogo, Method for producing automobile wheel disk, Japan Patent JP2004074248,2004 (in Japanese).

Forming of lightweight disk

*


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(a) 1st stage

(d) 4th stage

(b) 2nd stage

(e) 5th stage(c) 3rd stage

Decrease inthickness

Flat punchDie

Flat

punch Die

Drawn cup with flange

Outer punch

Outerdie

Innerpunch

Inner

punch

Outer

punch

Die

Middlepunch

Inner

punch

Innerdie

Outerdie

Outer

punchInnerdie Equal

Conventional multi-stage stampingof wheel disk


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Equivalent to inner corner

(c) 3rd stage(a) 1st stage (b) 2nd stage

Innerpunch

Inner die

Outerdie

Conicalpunch

Blankholder

Die

Conicalpunch

Die

Increase in wall thickness at inner corner

by means of conical punches

58.6 R5 R7

64.6

48.4R5

R7

55.4

50.1R2

R3.862.5

R3

~ 1/3.5 actual size of wheel disk

Increase inthickness

Largecompression

Outerpunch

Parameters for increase in thickness

2. Drawn volume ratio1. Punch angle,


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10 20 30

10

20

30

0Punch angle /

Punch

strokein2ndstage/mm

Drawn volume ratio, Vr0.470.44

0.410.38

Relationship between drawn volume ratio andpunch stroke

Total volume, VT

Drawn volume,V

Vr=V/VT

After 2nd stage

Drawn volume ratio

Conicalpunch

Die


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(a) 1st stage

Deformation behaviors for

=0 andVr=

0.44

(b) 2nd stage

(c) 3rd stage

Equivalent toinner corner


-6.3%

3.7%

14.3%15.0%3.9%

8.5%

2.6%

Innercorner


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Deformation behaviors for =25 and Vr=0.44

(a) 1st stage (b) 2nd stage

(c) 3rd stage



-3.9%

9.2%

15%5.9%13.7%

-2%

2.9%

Innercorner


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Cross sections for =25 and Vr=0.44


(c) 3rd stage (d) 4th stage

(e) 5th stage

~1/3 of 13 inch wheel disk


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Thickness distributions of drawn cup

having Vr= 0.41 for

= 0, 20 and 30

(b) Experiment

Around inner corner

(a) Calculated

Distance from center / mmChange

inwallthic

kness/%

Around innercorner

6%

0

o

20o30o

0 20 40 60-30

-20

-10

0

10

Distance from center / mmChange

inwallthic

kness/% Around inner

corner6%

0o

20

o

30o

0 20 40 60-30

-20

-10

0

10

Change in wall thickness:(t - to)to

x 100%=

tHat portion

Hub hole Hub hole


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Thickness distributions of drawn cup

having Vr= 0.44 for = 0, 20 and 30

(a) Calculated (b) Experiment

6mm

Innercorner

Punch angle / o

After 2nd stage

After 3rd stage

Chang

einwallthickness

atinnercorner/%

25

9.4%Maximumincrease

0 10 20 30

-10

0

10

Changeinwallth

ickness

atinnercorner/%

10

0

10

100 20 30

After 2nd stage

After 3rd stage

Punch angle /o

Maximumincrease9.0%


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Average increase in wall thickness at inner cornerfor = 0, 20, 30 and different Vr

0 10 20 30-10

-5

0

5

10

15

Punch angle/A

verageincreaseinwall

thic

knessatin

nercorner

/%

Vr=0.47

0.44

0.41

0.38

Stretching

Compression


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10 20 30

5

10

15

20

25

0

50

100

150

200

250

0

Punch angle/M

aximumincreasein

wallthick

ness

atin

nercorner

/%

Ma

ximumformingload

in3rdstage/kN

Forming load

Increase in thickness

Vr=0.47

Vr=0.44

Optimum condition

Optimum forming condition for increase in wall

thickness at inner corner of wheel disk


18/93

Chapter 2Multi-stage stamping of wheel disk having large innercorner thickness by means of conical punch

Average 10% increase in wall thickness aroundthe inner corner of the wheel disk was

successfully obtained by means of the conicalpunches.

The optimum forming conditions =25 and

Vr=0.44 were summarized. The blank thickness can be reduced without

decreasing the strength of the wheel for thereduction in weight

Conclusions


19/93


alloy cup having small bottom corner.

6.


5.


4.

Two-stage stamping of tailor circular blank for

increase in wall thickness at inner corner of wheeldisk.

3.


2.Introduction.1.

ContentsChapter




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Chapter 3Stamping of tailor circular blank for increase in wall


High material loss. Difficult to control laser welding process. High cost.

Disadvantages

Thin blank

Thick blank

Welding

Laser welding of tailor circular blank


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(a) 1st stage

(b) 2nd stage

(c) 3rd stage

Outer punch

Outer

dieInner die

Punch Die

Innerpunch


Blankholder

Punch

Die

(b) 2nd stage

(a) 1st stage

2-stage stamping of

tailor circular blank3-stage forming of

drawn cup with flange


Large inner cornerthickness

Wheel disk

Punch Die

Punch Blankholder

Die

Stamping of tailor circular blank for increase in wall



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Conditions for local thickening process

i) Stroke, sii) Clearance between punch

and die, c

Parameters :

18

54

R8 Blankc

Blankholder

PunchR4 R4

Die

Die

Restrictedby friction


c

Material wasdrawn intodie cavity

PunchBlankholder68

s

(a) 1st stage

(b) 2nd stage

Lowcompression

Highcompression

Equivalent portion


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Deforming behavior for local thickening process

(s = 6.5mm, c=2mm)

(a) 1st stage

-3.1%


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Deforming behavior for local thickening process

(s = 6.5mm, c=2mm)

(b) 2nd stage

12%


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Change

inwallthickness/%

Distance from bottom center / mm

3.54.55.56.5

7.5

s / mm

Equivalentportion

0 20 40 60-30

-20

-10

0

10

20

30

Calculated effect of stroke in 1st stage

of local thickening process

Equivalent portion

(c=2mm)


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Distance from bottom center / mmChang

einwallthickness/%

s / mm

Equivalentportion

12

Flat

3.54.55.56.57.5

0 20 40 60-30-20

-10

0

10

20

30

Effect of stroke in 2nd stage

of local thickening process

(a) Calculated (b) Experimental

Equivalent portion

Distance from bottom center / mmChang

einwallthickness%

3.54.55.56.57.5

s / mm

12

Equivalentportion

Flat

0 20 40 60-30-20

-10

0

10

20

30

(c=2mm)


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Effect of clearance in local thickening process

6.5Punch stroke in 1st stage s / mmMa

x.

increase

inwallth

ickness

intargetportion/% c / mm2

34

3 4 5 6 7 80

2

4

6

8

10

12

14

Tailor circular blank was formed with the conditionss = 6.5mm, c=2mm


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Stroke in 1st stage s / mm

Max

imumform

ingload

in

2ndstage

/kN

Maxim

umincrea

seinwall

thicknes

sintarget

portion/%

Load

Thickness

6.5

12

4 5 6 70

50

100

150

200

-30

-20

-10

010

20

30

Forming load in 2nd stage andincrease in wall thickness at target portion

for different punch strokes in 1st stage(c=2mm)


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15

mm

58.6

13.5

mm

64.6

120

(a) 1st stage (b) 2nd stage (c) 3rd stage

36.82R3.8

R2.0 R19.4

50.1

R8.0

Punch DieInnerPunch

Outer

punch

Outerdie

Inner die

Blank-holder

48.4

55.4

Conditions for 3-stage forming of drawn cup with

flange from tailor circular blank

1.6mm

Tailor circular blank

1

3.5

of actual disk

Punch Die


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Deforming behavior for 3-stage forming of drawn

cup with flange from tailor circular blank

1st stage

7.8%

(s=6.5mm, c=2mm)


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5.9%



2nd stage

(s=6.5mm, c=2mm)


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14%



3rd stage

(s=6.5mm, c=2mm)


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11

3

Around innercorner

Distance from bottom center / mmChangeinwallthickness

%

tailorflat

0 20 40 60-30

-20

-10

0

10

2030

Wall thickness distribution of drawn cup with flange

formed from tailor circular blank

Around inner corner

Hub hole


34/93

Chapter 3Two-stage stamping of tailor circular blank forincrease in wall thickness of wheel disk.

Extra 8% increase in wall thickness at the innercorner of wheel disk was successfully obtainedby the tailor circular blank.

Extra 2 stages of the local thickening processwere added to the conventional multi-stagestamping of wheel disk for the increase.

The cross sectional shape of the drawn cupformed from the locally thick blank is almost thesame with the one formed from the flat blank.

Conclusions


35/93

Two-stage stamping of cold drawn magnesiumalloy cup having small bottom corner.

6.


5.


4.

Two-stage stamping of tailor circular blank forincrease in wall thickness at inner corner of wheeldisk.

3.


2.

Introduction.1.

ContentsChapter




36/93

(c) 3rd stage(a) 1st stage (b) 2nd stage

Innerpunch

Outerpunch

Inner die

Outerdie

Conicalpunch

Die

Conicalpunch

Die

58.6

R5 R7

64.6

48.4R5

R

7

55.4

50.1R

2R3.862.5

R3

~ 1/3.5 actual size of wheel disk

2525


Equivalent to inner corner

Largecompression

25.

2

25.

2

( =25 and Vr=0.44)

Chapter 4

Multi-stage stamping of high strength steelwheel disk having large inner corner thickness


Forming conditions

Blankholder


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1.41.6Blank thickness / mm

=943.7 0.18 =629 0.15Flow stress / MPa590 Mpa408 MPaTensile strength / MPa

High strength

steel

Mild steelMaterial properties

Material properties


38/93

Thickness distributions of mild steel and

high strength steel drawn cups

12.57.2

Mild

High strength

Aroundinner corner

Distance from center / mmChangeinwallthickness/%

1.61.4

Thickness / mm

0 20 40 60-40

-20

0

20

Inner corner

Less increase in thicknessat inner corner!!!

Hub hole


39/93

Thickness distributions of drawn cups fordifferent blank thicknesses

Blank thickness / mmMax.

increasein

wallthickn

ess

atin

nercorner/%

Blank material=mild steel1.2 1.4 1.6 1.8 20

5

10

15

20

Inner corner

Decrease in blank thickness lead to small increase in thickness

at inner corner


40/93

Conditions for 2-stage stamping of tailor

circular blank for high strength steel wheel disk

18

54

R8 Blank3

Blankholder

Punch

R4 R4

Die

Die

Restrictedby friction


Material wasdrawn intodie cavity

PunchBlankholder68

s

(a) 1st stage

(b) 2nd stage

LowcompressionHighcompression

Equivalent portion

3

Punch stroke s is a parameter

1.4mm


41/93

-2%

Deformation behaviors of 2-stage stamping of

tailor blank for s=8.5

(a) 1st stage

Plasticequivalent strain

0.800

0.7330.6670.6000.5330.4670.4000.3330.2670.200

0.1330.0670.000

D f ti b h i f 2 t t i f


42/93

13%

Deformation behaviors of 2-stage stamping oftailor blank for s=8.5

1.570

1.0000.9090.8180.7270.6360.5450.4550.3640.273

0.1820.9090.000


(b) 2nd stage

Influence of punch stroke in 1st stage on


43/93

Punch stroke in 1st stage s / mm8.5

8.2

Averageincreasesinthick

ness

atequivalentportion

/%

Maximum

7 8 90

2

4

6

8

1012

14

Influence of punch stroke in 1st stage onamount of local thickening

Equivalent portion

Forming of tailor blank using s=8.5mm


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10%

Deformation behaviors of 3-stage stamping of

tailor blank for s=8.5Plasticequivalent strain

1.900

1.7401.5801.4201.270

1.1100.9500.7920.6330.4750.3170.1580.000(a) 1st stage

Deformation behaviors of 2 stages stamping of


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Deformation behaviors of 2-stages stamping oftailor blank for s=8.5

1.0901.0000.9090.8180.727

0.6360.5450.4550.364

0.2730.1820.0910.000

5%


(b) 2nd stage

Deformation behaviors of 2 stages stamping of


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Deformation behaviors of 2-stages stamping oftailor blank for s=8.5

2.260

2.0001.8201.6401.4501.2701.0900.9090.7270.545

0.3640.1820.000

18%


(c) 3rd stage


47/93

7.214.5

Distance from center / mmChangeinwallth

ickness/%

Aroundinner corner

Tailor

Flat

0 20 40 60-40

-20

0

20

Thickness distributions of drawn cups

formed from tailor and flat blanksInner corner

Amount of thickeningbecomes double !!!

Hub hole

C i f i i h l di k


48/93

Tailor blank

(a) Disk formed from

flat blank

94.1 21.9mm

21.0mm

94.1

(b) Disk formed from

tailor blank

Wrinkle

Cross sections of miniature wheel disk

formed from tailor and flat blanks

8mm

8m

m


49/93

Chapter 4Multi-stage stamping of high strength steel wheel diskhaving large inner corner thickness

The increase in wall thickness at the inner cornerof the high strength steel wheel disk becomessmall due to the decrease in blank thickness.

The high strength steel wheel disk formed fromthe tailor circular blank has 2 times of degree ofincrease in thickness at the inner corner ifcompared to the one formed from the flat blank.

The cross section of high strength steel wheeldisk formed from tailor blank is almost the same

with the one formed from flat blank.

Conclusions



50/93


6.

Multi-stage stamping of tailor square blank for

increase in wall thickness at bottom corner ofsquare cup.

5.


4.

Two-stage stamping of tailor circular blank forincrease in wall thickness at inner corner of wheeldisk.

3.


2.

Introduction.1.

ContentsChapter



Chapter 5


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Local thickening method

Chapter 5Multi-stage stamping of tailor square blank forincrease in wall thickness at bottom corner ofsquare cup

Rotate 90 for2nd thickeningoperation

(a) After 1st stage (b) After 2nd stage1st thickened portion

Constraint

Compression

1st thickening operation

C diti f thi k i ti


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(c) Dimension of ditch in detail

Inner die

Punch

46.0

34.032.0

48.0

0.1

5

0.1

5

Outer die

PunchHolder

Punch

Die

R5.0R

6.6

34.0

46.0

45.333.3

R5.0 R6.6

90.0

80.0

(b) 2nd stage

1stthickened

portion 49.6

76.4

0.2Ditch

Stopper

1.6

(a) 1st stage

Inner die

4.6

Squareblank

Conditions for thickening operation

=40, 45, 50, 55, 60

Parameter

symmetry along vertical axis

Deformation behavior for multi-stage stamping


53/93

Deformation behavior for multi stage stamping

of tailor square blank for= 55

(a) 1st stage

1

4model



54/93

(b) 2nd stage

20%increase inthickness



model



55/93

(c) 3rd stage



Ditch

1

4model



56/93

Ditch

Ditch

Ditch

1st thickened portion33% increasein thickness



(d) 4th stage

1

4model

D f d t il bl k bt i d f


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X

Y

Z

Max. 33% increasein thickness

~1mm

~1mm

Bulging

75m

m

75mm

Deformed tailor square blank obtained from

simulation for= 551

4model

Cross sections of tailor square blank after 1st


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(a)= 50

(b)= 55

(c)= 60

Buckling71.8

74.0

76.8

Cross sections of tailor square blank after 1st

thickening operation for different

Thickness distributions of tailor square blank


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Thickness distributions of tailor square blank

after 1st thickening operation for different

D istance from center / m mChangeinwallthickness/%

18

/

Target

portion

0 10 20 30 40

0

10

20

30

455055

Thickness distribution along 1st thickened


60/93

Thickness distribution along 1st thickened

portion of tailor square blank after 2ndthickening operation

Distance along X=18 from Y=0

33

0 10 20 30 40

10

20

30

40 Cross between 1stand 2nd thickened

portions

Less increase inthickness due to

bulging

Portion equivalent

to inner cornerChangeinwall

thickness/%

Deformation behavior for deep drawing of


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10% Increase inthickness

p g

square cup from tailor square blank

X

Y

Z

R6

R636mm

Punch

Die

R6

75mm

36mm

R6

54mm54m

m

75mm

R

6

R6

(a) Conditions (b) Deformation behavior

C i f f d f


62/93

(a) Formed from tailor blank (b) Formed from flat blank

+10% -17%

Die

of cup

Punch

Blank holder

Bottomcorner

Cross sections of square cup formed fromtailor blank and flat blank

Highstrength Lowstrength

Thickness distribution of square cup formed


63/93

Thickness distribution of square cup formed

from tailor square blank

Distance of bottom edge along X=18 / mm

Changeinwallthickness/%

Cup formed fromflat blank

Cup formed fromtailor blank

Tailor blank

-17Bottom corner

10

0 10 20 30 40

-20

0

20

40

Conclusions


64/93

Chapter 5Multi-stage stamping of tailor square blank forincrease in wall thickness at bottom corner of squarecup

The tailor square blank was successfully formedby stamping process.

The tailor square blank having maximum 33%increase in wall thickness at the portionequivalent to the bottom corners of the squarecup was formed.

The square cup formed from the tailor blankhave 10 % increase in wall thickness at bottomcorners if compare to the one formed from flat

blank having 17% decrease in wall thickness.

Conclusions



65/93


6.

Multi-stage stamping of tailor square blank for

increase in wall thickness at bottom corner ofsquare cup.

5.


4.

Two-stage stamping of tailor circular blank forincrease in wall thickness at inner corner of wheel

disk.

3.


2.

Introduction.1.

ContentsChapterof lightweight parts

Chapter 6


66/93

Chapter 6

Two-stage stamping of cold drawn magnesiumalloy cup having small bottom corner

PunchBlankholder

Die

Coolant

Heater

Casing of laptop formedby hot stamping process

Heating apparatus is expensive and complicated

Disadvantage

Conditions for two-stage stamping of cold drawnmagnesium alloy cup having small bottom corner


67/93

magnesium alloy cup having small bottom corner

(a) 1st stage

Die

Blankholder

Drawn cup

Outer punch

Container

Inner punch

Coil spring

bRp=5mm

Crack

aRp=1mm

Rp=5mm

Punch

Drawn ratio =1.72 (b) 2nd stage

18.620.0 R4

19.818.810.0

s

Smallbottomcorner

Deformation behavior for round magnesium


68/93

cup having small bottom corner


Cross sections of round magnesium cup having


69/93

Cross sections of round magnesium cup having

small bottom corner

R1.1

7.

2

18.918.9R5.0

9.

4

s=2.6m m (a) 1st stage (b) 2nd stage

Height and bottom corner radius of round cup


70/93

Height and bottom corner radius of round cup

for different punch strokes in 2nd stage

0.5 1 1.5 2 2.5 3

2

4

6

8

10

0

1

2

3

4

5

6

0Punch stroke in 2nd stage / mm

Heightofcup/mm

Bottomcorner

radius/m

m

Bottomcorner radius

Height of cup

Crack at bottom corner

s=2.8mm

Limit forcrack

Experimental

Calculated

2.8

Introducing conical punch and ironing die in 1st stageof cold stamping of round magnesium alloy cup


71/93

a= 140

(b)= 150

R=5

R420.0

18.6

Blank Holder

Ironingdie

Conicalpunch

Blank

Crack

19.69

Drawingdie

of cold stamping of round magnesium alloy cup

Maximum

to= 0.5

b

Ironing ratio, a= (to-b)/ to

Cross sections of round magnesium cup


72/93

R1.1

7.

2

18.9

7.3

0.6

18.9

(a) By flat punch

for s=2.6mm

(b) By conical punch

for s=2.9mm

(c) By conical punch

for s=3.4mm anda=20%

Straight

7.8

0.5

18.7

Cross sections of round magnesium cup

obtained from experiment

Conditions for two-stage stamping of magnesium


73/93

square cup having small bottom corner radius

R3.4

R4

R4R4

18

.8

18.8

20.0

20

.0

(a) 1st stage

(b) 2nd stage

Squarecup

Outer punch

1018.8

19.8

Container

Innerpunch

27

R8.1

Square blankSmall

bottom

corner

Magnesium square cups obtained from experiment


74/93

R3.7

5.

2 R0.6

3.

8


Conclusions


75/93

Chapter 6Two-stage stamping of cold drawn magnesium alloycup having small bottom corner

The round and the square magnesium alloy cupshaving small bottom corners were successfullyformed at room temperature.

An extra stage is added for reducing the bottomcorner radius.

The employment of the conical punch and theironing die improved the dimensions of the cup

List of publications


76/93

Reviewed journals:1. Chin Joo Tan, Yohei Abe, Ken-ichiro Mori, Takayuki Nonaka and Osamu Ebihara,Increase of wall thickness around corner of multi-stage drawn cup with flange usingconical punches, Key Engineering Materials, vol. 340-341, p. 761-766, 2007.

2., Chin Joo Tan,,,,,,., Journal of Japan Society for

Technology of Plasticity, vol. 48, no. 561, p. 55-59, 2007.3. C. J. Tan, K. Mori and Y.Abe, Multi-stage stamping of high strength steel wheel disk,

Journal of advanced manufacturing technology (Spec. ed.), vol. 1, no. 1, p.31-47,2007. (ISSN:1985-3157).

4. C. J. Tan, K. Mori and Y.Abe, Forming of tailor blanks having local thickening forcontrol of wall thickness of stamped products, Journal of Material ProcessingTechnology, in press. 2007.

Reviewed Conference papers:5. C. J. Tan, K. Mori and Y.Abe, Increase in wall thickness at inner corner of multi-stage

stamping of wheel disk by locally thick blank, Proc. 2nd International Conference on

New Forming Technology (ed. F. Vollertsen et al.), p.371-380, 2007.6. C. J. Tan, K. Mori and Y.Abe, Forming of high strength steel wheel disk having largeinner corner thickness. Proc. International Conference on Engineering & ICT, vol. 1,p.41-48, 2007. (Best paper award).

Drawn cup for =25 and Vr=0.44


77/93

(b) 1st stage(a) Blank

(c) 2nd stage (d) 3rd stage

12mm

Effect of angle of bulging ring in local


78/93

Max.in

creasein

wallthic

kness

in

targetpo

rtion/%

Angle of bulging ring / o43

c / mm

234

0 10 20 30 40 50 60

2

46

8

10

12

14

thickening process

Reason for decrease in thickness for s = 7.5mm

(c=2mm)


79/93

(i) s= 7.5mm (ii) s = 6.5mm

53 43

DieOuterpunch

DieOuterpunchInner punch

Equivalentportion


Inner punch

Highcompression

LowcompressionHighcompression

Lowcompression


( )

Photographs of deformed discs


80/93


10mm

2-stages local thickening process (s=6.5mm, c=2mm)

10mm


(ii) Formed fromflat blank

(i) Formed fromlocally thick blank

Thickness distributions of drawn cups fordifferent materials


81/93

Aroundinner corner

Mild

Highstrength

Distance from center / mmCha

ngeinwal

lthickness

/%

Blank thickness = 1.4mm

0 20 40 60-40

-20

0

20

Inner corner

High strength steel has no influence on the increase in thickness

Forming of high strength steel drawn cupfrom tailor circular blank


82/93

Outer punch

Outerdie

Inner die

Inner

punch


Blankholder

Punch

Die

(b) 2nd stage

(a) 1st stage

2-stage stamping oftailor circular blank 3-stage forming of

drawn cup with flange


Large inner cornerthickness

High strength steel

wheel disk

Punch Blankholder

Die

(a) 1st stage

Conicalpunch Die

Holder

Die

(b) 2nd stage

(c) 3rd stage


Forming load in 2nd stage for s = 8.5mm


83/93

Die

PunchBlankholder

2 4 6 8 10

50

100

150

200

0

Punch stroke s / mm

Form

ingload/k

N2nd

1st

Miniature wheel disks formed fromtailor and flat blanks


84/93

(a) Formed from flat blank

10mm

10mm

(b) Formed from tailor blank

Deformation behaviors of thickening operation


85/93

for=55

(b) 2nd stage(a) 1st stage

18%

Targetportion

Chapter 5Multi-stage stamping of tailor square blank for


86/93

increase in wall thickness at bottom corner ofsquare cup

80

40

6 6

40

(a) 1st thickening operation (b) 2nd thickening operation

90rotation

6 6

1st thickenedportion

2nd thickenedportion

Equivalent to bottom corners of square cup

Double thickening

80

4

0

Equivalent tobottom edgesof square cup

Distribution of thickness and hardness of round

i i


87/93

cup in two-stage stamping process

Thickness/mm

2 4 6 8 10 12 14 16

0.2

0.4

0.6

0.8

1

0

20

40

60

80

100

0Distance from bottom center / mm

Hardness/Hv

Hardness

Thickness

1st stage2nd stage

Initial thickness

Aroundbottom corner

Deformation behaviors of cup for= 150


88/93

(a) 1st stage

0.5490.5060.4630.4200.377

0.3340.2910.2480.205

0.1620.1190.0760.033


Deformation behaviors of round magnesium cupfor= 150

Pl ti


89/93

(b) 2nd stage

0.9500.879

0.8080.7370.6660.596

0.5250.4540.3830.3120.241

0.1710.010


Relationship between height of cup and bottomcorner radius for different punch strokes in 2nd

t f 20% & 150


90/93

stage for a=20% &= 150

1 2 3 4

2

4

6

8

0

0.5

1

1.5

2

0Punch stroke in 2nd stage s / mm

Heightof

cup

/mm

Bottomcornerradius/mmHeight

RadiusLimit for

crack

Crack

Distribution of thickness strain and hardness of cup

ft 1 t d 2 d t f 20% &

150


91/93

after 1st and 2nd stage for a=20% & = 150

0 2 4 6 8 10 12 14 16 18-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0

20

40

60

80

100


Thicknessstrain

Hardness/HV

Hardness

Strain

1st2nd

Bottom cornerafter 2nd stage

Distribution of thickness strain and of

h d l ti f


92/93

hardness along cross section of square cup

0 2 4 6 8 10 12 14-0.3

-0.2

-0.1

0

0.10.2

0.3

0

20

40

60

80

100


Thickn

essstrain

Hardness/Hv

Thickness strain

Hardness

1st2nd

Aroundbottom corner

Relationship between forming load in 3rd

stage and conical punch angle


93/93

10 20 30

50

100

150

200

250

0Punch angle/

Formingloadin3rdstage/kN

Vr

=0.47

0.44

0.41

0.38

stage and conical punch angle

study of sheet metal stamping processes

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