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J o u r n a l o f

Materials

Processing

Technology

E L S E V IE R Journal of M ateria ls Processing Techology 52 (1995) 359-367

n e w t e c h n o l o g y o f s h e e t - m e t a l f le x ib l e- d ie f o r m i n g u s i n g

a v i s c o p l a s t i c p r e s s u r e - c a r r y i n g m e d i u m

M i n g - W a n g F u a'* , S i- Q u a n g L u a, M a o - H e n g H u a n g b

Nanchang Institute of Aeronautical Technology, Nanchan9 330034, People s Republic of China

b Governor Office of Jiangxi Province, Nanchang 330046, People s Republic of China

Received 13 January 1994

Industrial Summary

T h e c o n v e n t i o n a l p r e s s u r e - c a r r y i n g m e d i a o f s h e e t- m e t a l f o r m i n g a r e s o l id m a t e r i a ls ( a

r u b b e r o r p o l y u r e t h a n e p a d ) , l i q u i d (o i l a n d w a t e r ) a n d g a s ( p re s s u r e d a i r a n d e x p a n d i n g a i r) .

T h e v a r i o u s f l e x ib l e -d i e f o r m i n g m e t h o d s u s i n g th e a b o v e p r e s s u r e - c a r r y in g m e d i a h a v e a l o t o f

d i ff e re n t c h a r a c t e ri s t ic s a n d h a v e p r o m o t e d t h e d e v e l o p m e n t o f s h ee t m e t a l f o r m i n g t e c h n o -

l o g y . T h e r e a r e , h o w e v e r , a l o t o f d i s a d v a n t a g e s i n u s i n g th e s e p r e s s u r e - c a r r y i n g m e d i a . I n o r d e r

t o e x p l o r e a ne w p r e s s u r e - c a r r y i n g m e d i u m , n u m e r o u s e x p e r i m e n t s h av e b e e n u n d e r t a k e n , a s

a r e s u l t o f w h i c h a n e w t y p e o f p r e s s u r e - c a r r y i n g m e d i u m c a l l e d a v i s c o p l a s t i c p r e s s u r e - c a r r y i n g

m e d i u m ( V P C M ) h a s b e e n s y n t h e s i z e d . I n t h i s p a p e r , a n ew k i n d o f f l e x ib l e - d i e f o r m i n g

t e c h n o l o g y us i n g V P C M h a s b e e n p u t f o r w a r d a n d u s e d to m a n u f a c t u r e m a n y d i f fe r en t

w o r k p i e c e s . T h e e x p e r i m e n t a l r e s u l ts h a v e s h o w n t h a t t h i s k i n d o f t e c h n o l o g y h a s a l o t o f

a d v a n t a g e s , s u c h a s a s m a l l d r a w i n g c o e f f ic i e n t, g o o d s u r f a c e f in e n es s , h i g h d i m e n s i o n a l -

a c c u r a c y , a n d a s i m p l e a n d a g e n e r a l - s e r v i c e d i e s t r u c t u r e . M o r e o v e r , T h i s t e c h n o l o g y c a n a l s o

b e u s e d t o m a n u f a c t u r e c o m p l i c a t e d w o r k p i e c e s w i t h a l a r g e d e g re e o f d e f o r m a t i o n o r s u b s t a n -

t i a l lo c a l d e f o r m a t i o n . A c c o r d i n g t o t h e p r a c t i c a l u s e s o f th i s t e c h n o l o g y , t h r e e s e ts o f d i e a r e

d e s c r i b e d a l s o i n t h i s p a p e r .

1 . I n t r o d u c t i o n

S h e e t m e t a l w o r k i n g i s t h e b a c k b o n e o f m a n y i n d u s t r i a l f ie ld s s u c h a s e le c t ro n i c s ,

a u t o m o b i l e s , a g r i c u l t u r e m a c h i n e s a n d t h e a e r o n a u t i c a l a s t r o n a u t i c a l in d u s t r y . S i n ce

t h e r e q u i r e m e n t s f o r d i m e n s i o n a l a c c u r a c y , s u r f a c e f in e n es s a n d s h a p e c o m p l i c a t i o n o f

s h e e t m e t a l p r e s s - w o r k i n g w o r k p i e c e s a r e b e c o m i n g i n c r e a s i n g l y h i g h e r , m o r e l o w -

p l a s t i c i t y a n d b a d - f o r m a b i l i t y s h e e t m e t a l s n e e d t o b e f o r m e d . C o n c e r n i n g t h e t h i r d

r e q u i r e m e n t , t h e m a n u f a c t u r i n g f ie ld h a s c o m e b a c k t o t h e s t a t e o f m o r e t y p e s a n d l es s

*Correspond ing au thor .

0924-0136/95/$9.50 (~ 1995 Elsevie r Science S.A. All r ights reserve d

SSDI

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360 M .-W, Fu et a l. /Jou rna l (?[Materia ls Proce ss ing Technology 52 (1995) 359 367

o u t p u t , e s p e c ia l ly in t h e a e r o n a u t i c a l a n d a s t r o n a u t i c a l i n d u s tr y . C o n v e n t i o n a l p r e s s-

w o r k i n g t e c h n o l o g y d o e s n o t s a ti sf y th e n e e d s o f i n d u s tr i a l d e v e l o p m e n t .

F l e x i b le d i e fo r m i n g ( F D F ) is a n i m p o r t a n t t e c h n o l o g y o f s h e et m e t a l f o r m i n g . It

u s e s t h e p r e s s u r e - c a r r y i n g m e d i u m ( P C M ) t o r e p l a c e a r i g i d p u n c h o r d i e . T h e

c o n v e n t i o n a l p r e s s u r e - c a r r y i n g m e d i u m is l i q u id ( w a t e r , oi l) , g a s ( p r e s s u r e d o r e x -

p a n d i n g a ir ) a n d a n e l as ti c b o d y ( a r u b b e r o r p o l y u r e t h a n e pa d ). T h u s , F D F u s es

a d if f e r e n t P C M a n d h a s d i f fe r e n t c h a r a c t e r i s ti c s . L i q u i d is u s e d a s t h e P C M f o r

h y d r o - m e c h a n i c a l d r a w i n g [ 1 , 2 ] . A l t h o u g h i t h a s b e e n u s e d w i d e l y , t h e r e a r e s o m e

d i s a d v a n t a g e s s u c h a s l i q u i d s p l a s h w h e n f o r m i n g f a il s a n d d i f fi c u lt y i n c o n t r o l l i n g t h e

l i q u i d p r e s s u r e d u r i n g f o r m i n g . T h i r d l y , i t i s t r o u b l e s o m e t o p e r f o r m t h e p r e s s i n g

o p e r a t i o n d u e t o c o n c e r n a b o u t p o s s i b l e l i q u i d l e a k a g e . R u b b e r i s u s e d a s P C M f o r

t h e G u e r i n p r o c e s s a n d p o l y u r e t h a n e is o f te n u se d a s t h e P C M f o r F D F [ 3 7 ] , b u t

d e e p - d r a w i n g p a r ts a n d c o m p l i c a t e d w o r k p ie c e s , h o w e v e r , c a n n o t b e p r o d u c e d b y

t h is F D F t e c h n o l o g y b e c a u s e o f t h e d e f o r m a t i o n l im i t o f P C M its elf . R u b b e r - p a d

f o r m i n g i s a l s o u s e d w i d e l y i n a e r o p l a n e f a c t o r i e s . I t s e q u i p m e n t , h o w e v e r , i s v e r y

e x p e n s i v e a n d w o r k p i e c e s w i th g r e a t lo c a l d e f o r m a t i o n c a n n o t b e m a n u f a c t u r e d b y

t h is p r o c es s . G a s is u s e d a s th e p r e s s u r e - c a r r y i n g m e d i u m f o r s u p e r p l a s t i c b u l g i n g a n d

e x p l o s i v e f o r m i n g , b u t i t s e f f i c i e n c y is l o w a n d i ts t h i c k n e s s r e d u c t i o n is g r e a t .

K u r o s a k i e t a l . h a v e u s e d a v i s c o p l a s t i c m e d i u m ( V M ) t o r e p l a c e t h e r i g i d p u n c h t o

p i e r c e v e r y s m a l l h o l es in s h e e t m e t a l [ 8 11 ] , w h i c h i s a n o t h e r g o o d u s e o f F D F . O n

t h e b a s is o f t h e a b o v e s t a te m e n t , a n a t t e m p t is m a d e in a n e x p l o r a t o r y w a y t o d i s c o v e r

a n e w p r o c e s s o f s h e e t - m e t a l f l ex i b l e -d i e f o r m i n g u s i n g a n e w k i n d o f v i s c o p l a s ti c

m a t e r i a l s y n t h e s iz e d b y t h e p r e s e n t a u t h o r s a s t h e P C M . T h i s P C M h a s a v is c o p l as t ic

m e c h a n i c s b e h a v i o u r a n d i t i s c a l l e d a v i s c o p l a s t i c p r e s s u r e - c a r r y i n g m e d i u m

( V P C M ) . A g r e a t d e a l o f e f f o r t h a s b e e n p u t i n t o b o t h e x p l o r i n g t h e p r i n c ip l e s a n d

e x p e r i m e n t a l s t u d y . A lo t o f w o r k p i e c e s w i th a l o w d r a w i n g c o e f f i c i e n t a n d a c o m p l i c -

a t e d s h a p e h a v e b e e n f o r m e d b y t h is t e c h n o l o g y . T h e w o r k p i e c e s s h o w n i n F i g . 4 h a v e

b e e n m a n u f a c t u r e d b y f le x ib l e d i e f o r m i n g u s i n g t h e V C P M . T h e s e w o r k p i e c e s a r e

m a n u f a c t u r e d i n t he s a m e d i e, b y m e a n s o f c h a n g i n g t h e p u n c h , t h e b l a n k - h o l d e r a n d

the f l ange .

2 . Th e ch aracteri st ic s an d adv an tages o f th i s n ew tech n o logy by com par i son wi th

con v en t ion al FDF

F D F u s i ng th e V P C M h a s a l o t o f a d v a n t a g e s :

(1 ) T h e m a i n c h a r a c t e r i s t i c s o f th e d i e a r e a s i m p l e s t r u c t u r e , l o w c o s t , a s h o r t

m a n u f a c t u r i n g p e r i o d a n d u n i v e r s a l u s a g e , s o t h a t d i f f e r e n t w o r k p i e c e s c a n b e

m a n u f a c t u r e d in t h e s a m e d ie s et b y c h a n g i n g t h e p u n c h , t h e fl a ng e a n d t h e b l a n k -

h o l d e r .

(2 ) G r e a t f o r m a b i l i t y . B e c a u s e t h e V P C M c h a n g e s t h e fl o w p a t t e r n a n d s t re s s s ta t e s

o f t h e s h e e t m e t al , t h e f o r m a b i l it y c a n b e i m p r o v e d g r e a tl y . F o r e x a m p l e , th e d r a w i n g

c o e f f ic i e n t o f 0 8 A I is 0 .5 7 - 0 . 5 8 f o r c o n v e n t i o n a l d r a w i n g , 0 .4 1 f o r h y d r o - m e c h a n i c a l

d r a w i n g , b u t is 0.3 8 fo r th i s k in d o f F D F . F o r t h e h e m i - s p h e r ic a l w o r k p i e c e o f

s t a i n l e s s s t e e l s h e e t m e t a l w i t h a b a r r e l - s h a p e d b o t t o m i n F i g . 4 ( a ) , t h e d r a w i n g

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M.-VK Fu et al./Journal of Materials Processing Technology 52 (1995) 359 367 361

co e f f i c i en t o f t h e b a r r e l is 0 .2 1. Th i s i l l u s t r a t e s t h a t s h e e t m e ta l f o r m ab i l i t y u s in g t h i s

n e w t e c h n o l o g y is m u c h b e t t er t h a n t h a t o f c o n v e n t i o n a l d r a w i n g a n d h y d r o - m e c h a n -

i c a l d r a w i n g .

(3) I n c r e a s in g o f t h e d i m e n s i o n a l a c c u r a c y o f p r o d u c t s a n d d e c r e a s in g o f th e

s p r in g - b a c k . T h e V P C M o f t h is t e c h n o l o g y im p r o v e s t h e s tr es s s t a te a n d t h e s tr es s

d i s t r ib u t i o n , so t h a t i t in c r ea s e s th e d i m e n s i o n a l a c c u r a cy . F o r F D F , t h e d i m e n s i o n a l

a c c u r a c y c a n r e a c h I T 9 - 1 0 , b u t i t s v a l u e i s o n l y I T l l - 1 2 f o r c o n v e n t i o n a l d r a w i n g

t e c h n o l o g y .

(4 ) G o o d s u r f a c e f in e n e ss . I n c o n v e n t i o n a l d r a w i n g , t h e s h e e t m e t a l is d e f o r m e d b y

t h e w a y o f f l o w i n g a l o n g t h e c o r n e r o f t h e r i g i d d i e, s o t h a t t h e s u r f a c e o f s h e e t m e t a l is

e a s i l y s c r a t c h e d . H o w e v e r , fo r t h is t e c h n o l o g y , th e s h e e t m e t a l is d e f o r m e d b y t h e w a y

o f f o r m i n g a " c o n v e x r i d g e " i n t h e d r a w i n g p r o c e s s . T h e r e f o r e , th e s h e e t m e t a l d o n o t

f l o w a l o n g t h e c o r n e r o f f l a n g e a n d i ts s u rf a c e is n o t s c r a t c h e d a n d r e t a i n s t h e o r i g i n a l

s u r f ace f i n en es s o f t h e s h ee t m e ta l .

(5 ) S m a l l w a l l- t h ic k n e s s r e d u c t i o n . T h e h i g h p r e s su r e g e n e r a t e d b y V P C M m a k e s t h e

s h e et m e t a l w r a p t h e p u n c h t i g h t l y a n d t h e f ri c t io n a l e ff ec t b e t w e e n t h e p u n c h a n d t h e

s h ee t me ta l mak es t h e r ad i a l t en s i l e s t r e s s d ec r ea s e . O n th e o th e r h an d , t h e s t r a in - r a t e

s e n s it iv i ty o f V P C M m a k e s i t e a s y to s e t u p h i g h p re s s u re i n t h e m e d i u m c o n t a i n e r a n d

to i n c r ea s e t h e v i s co -f r ic t i o n e f fec t b e tw een th e V P C M an d th e s h ee t me ta l , w h ich

p r o d u c e s t h e r e s is t a n ce t o t h e w a l l - th i c k n e ss r e d u c t i o n o f t h e s h e e t m e t a l. O n a c c o u n t o f

th e ab o v e , t h e w a l l - t h i ck n es s r ed u c t io n i s s ma l l in t h i s t e ch n o lo g y . F o r t h e f l a t cu p p in g

o f 0 8 A 1 s h ee t m e ta l f o r w h ich t h e d r aw in g co e f fi c i en t i s 0 .5 7, t h e m ax im u m w a l l -

t h i c k n e s s r e d u c t i o n i s a b o u t 1 5 2 0 % , b u t t h e m a x i m u m w a l l - t h i c k n e s s r e d u c t i o n i s

o n l y 8 % w h e n t h e d r a w i n g c o e f fi c ie n t is 0.3 8 f o r t h e p r e s e n t t e c h n o l o g y . T h e d r a w i n g

co e f fi c i en t o f t h e co n e - s h a p ed w o r k p iece i n F ig . 4( f) is 0 .4 0 an d t h e m ax im u m w a l l -

t h i ck n es s r ed u c t io n a t t h e t o p o f t h e w o r k p iece is l es s t h a n 3 4 % .

(6 ) A l o t o f l o w - p l a s t i c i t y a n d b a d - f o r m a b i l i t y m a t e r i a l s o r h i g h - s t r e n g t h m a t e r i a l s

c a n b e d e f o r m e d b y t h i s t e c h n o l o g y .

( 7 ) W o r k p e i c e s w i t h c o m p l i c a t e d o r u n u s u a l s h a p e s c a n b e m a n u f a c t u r e d b y t h i s

t ec h n o lo g y , s u ch a s t h e w o r k p iec es s h o w n in F ig s . 4 ( d) , ( f) -( i) .

3 . T h e r e q u i r e m e n t s f o r a v i s c o p l a s t i c p r e s s u r e - c a r r y i n g m e d i u m

I n vi ew o f t h e d i s a d v a n t a g e s o f t h e P C M o f c o n v e n t i o n a l F D F a n d t h e ex p e ri e n ce s

o f h y d r o - m e c h a n i c a l d r a w i n g r e s e a rc h , t h e a u t h o r s t h i n k t h a t t h e i de a l V P C M s h o u l d

m e e t t h e f o l l o w i n g r e q u i r e m e n t s :

(a ) r e la t i v e l y h i g h s t r a i n - r a t e s e n s it i v it y ; (b ) lo w a d h e s i o n t o t h e m e t a l s u r f a c e a n d

a g o o d a b i l i t y t o b e e a s i l y s h e d f r o m t h e s u r fa c e o f t h e w o r k p i e c e s a n d t h e d ie ; (c ) g o o d

s t i ck y a b i l i t y a n d s t ab i l i t y ; (d ) p r o p e r s t i ck in es s an d co h es io n , i.e ., d i f f icu l t t o s p l a s h ; (e )

h a r m l e s s t o h u m a n h e a l t h a n d n o n - p o l l u t i n g o f t h e e n v i r o n m e n t ; (f) g o o d r e p e a ta b i l -

i ty in use:

O n t h e b a s is o f t h e a b o v e r e q u i r e m e n t s a n d n u m e r o u s e x p e r i m e n t a l r e su l ts , t h e

a u t h o r s h a v e s y n t h e s iz e d a k i n d o f v is c o p la s t ic p r e s s u r e -c a r r y in g m e d i u m . E x p e r i -

m e n t a l r e s u l t s h a v e s h o w n t h a t t h e V P C M m e e t s t h e a b o v e r e q u i r e m e n t s .

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362

~L-W. Fu et al./Journal qf Materials Processing Technology 52 (1995) 359 367

unch U p p er ' b o l s t ~ 'r

" S t

S c r e ~ 2

F i g . 1. R i g i d b l a n k - h o l d i n g s t r u c t u r e .

4 . D i e s tr u c t u r e

A s s t a t e d a b o v e , f l e x ib l e - d ie f o r m i n g u s e s a p r e s s u r e - c a r r y i n g m e d i u m t o r e p l a c e t h e

r i g i d - p u n c h o r r i g id - d i e, F i g . 1 is t h e F D F d i e f o r u s in g t h e V P C M . I n t h e f ig u r e , t h e

s h e e t m e t a l i s p l a c e d o n t h e m e d i u m c o n t a i n e r w h i c h is fu ll o f V P C M . A f t e r t h e p u n c h

h a s b e e n i n s e rt e d i n t o t h e c o n t a i n e r , th e h i g h p r e s s u r e o f t h e V P C M is c r e a te d ,

w h e r e u p o n t h e V P C M p r es s es t h e b l a n k a g a i n s t th e s u rf a c e o f t h e p u n c h t o fo r m t h e

w o r k p i e c e t o t h e s h a p e o f t h e p u n c h . T h e c h a r a c t e r i s t i c s o f t h e d ie s t r u c t u r e a r e a s

f o l l o w s :

( 1 ) G e n e r a l s e r v i c e . D i f f e r e n t w o r k p i e c e s c a n b e m a n u f a c t u r e d u s i n g a d i f f e r e n t

p u n c h , b l a n k - h o l d e r a n d f la n ge . T h e w o r k p i e c e s s h o w n i n F ig . 8 h a v e b e e n m a n u f a c -

t u r e d b y t h i s w a y .

(2 ) B l a n k - h o l d i n g F o r c e . T h e b l a n k - h o l d i n g f o r c e f o r t h e d i e se t is g e n e r a t e d b y

a ri g id b l a n k - h o l d i n g s t r u c t u r e a n d c a n b e c o n t r o l l e d a c c o r d i n g t o t h e sh e e t m e t a l a n d

t h e w o r k p i e c e s .

(3 ) F i l li n g o f V P C M . F o r l a rg e m a s s p r o d u c t i o n , t h e V P C M d o e s n o t f lo w o u t f r o m

t h e c o n t a i n e r . A f t e r t h e p u n c h h a s b e e n i n s e r t e d i n t o t h e c o n t a i n e r t h e p u s h e r b a r

m o v e s d o w n , a n d a f te r d e f o r m a t i o n h a s c e a s ed t h e p u s h e r b a r m o v e s u p t o l et t h e

V P C M r is e u p t o th e fl an g e p l an e . F o r s m a l l m a s s p r o d u c t i o n , t h e V P C M c a n f lo w

o u t o f t h e c o n t a i n e r t h r o u g h t h e t h r o t t i n g s e t m o u n t e d i n th e t h r o t t i n g h o le . T h e

f il li ng o f t h e V P C M is fi n is h e d b y m a n u a l o p e r a t i o n .

(4 ) C o n t r o l l i n g o f t h e p r e s s u r e . A s th e f il li ng o f V P C M is p e r f o r m e d b y t h e

m o v e m e n t o f t h e p u s h e r b a r , t h e p r e ss u r e o f t h e V P C M i n si d e t h e c o n t a i n e r is

c o n t r o l l e d b y th e t h r o t t i n g , s e t a c c o r d i n g t o t h e s t r e n g t h , t h e f o r m a b i l i t y o f t h e s h e et

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M . -W . F u e t a l . / J o u r n a l o f M a t er i a l s P r o c essi n g T e ch n o l o g y 5 2 1 9 95 ) 3 5 9 - 3 6 7 363

Sprin9

2 ~ ,

Sprin9 1 ~

Blank holder

/ ~ /

Flan9e

Seal ri~19

2 ~

Seal r i n g ~

tpper

bolster

• ~ ~ i / l i o lt q olJt

Fig. 2 Elastic blank -holding structure.

Bar

l:0~e;' mlsl,,;,

F / - ' f l / A I F 5 1 1 7 . / ' 7 1 B;a;~ k h i n te r,

Pu ~ V

IVA ~ V / A - - - - ~

~ iIil~COIl~ ltel'

Pressure

measkl~r~v~ h e r

Fig. 3. Die suitab le for a twin-drive press

m e t a l a n d t h e w o r k p i e c e s s h a p e . T h e h a n d l i n g o f t h e b l a n k - h o l d e r i n F ig . 1 m u s t b e

p e r f o r m e d f o r e v e r y f o r m i n g o p e r a t i o n . T h e p r o d u c t i o n e f fi c ie n c y is l o w a n d i t t a k e s

3 - 5 m i n t o p e r f o r m o n e f o r m i n g o p e r a t i o n . T h u s i t c a n n o t b e s u i t a b le t o l ar g e m a s s

p r o d u c t i o n . T h e b l a n k - h o l d e r i n F i g . 2 i s e l a s t i c . T h e b l a n k - h o l d i n g f o r c e c a n b e

c o n t r o l l e d b y h o l d i n g d o w n t h e sp r i n g o f t h e b l a n k - h o l d i n g s et . T h e f il li ng o f t h e

V P C M a n d t h e c o n t r o l l i n g o f i ts p r e ss u r e a r e t h e s a m e a s f o r t h e fi rs t d i e se t. T h e m a i n

c h a r a c t e r i s t i c o f t h i s d i e s e t i s t h a t i t i s m o r e e f f i c i e n t t h a n t h e f i r st d i e s e t. F i g . 3 i s

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3 6 4

M.-W, Fu et al./Journal of Materials Processing Technology 52 (1995) 359 367

a )

b )

c ) d )

e ) f )

Fi g . 4 . Workp i e c e s ma nufa c t u re d b y t he ne w t e c hno l ogy .

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M.-W. Fu et al. /Journal of Materials Processing Technology 52 (1995) 359-367

365

g )

h )

i )

J )

(k) (0

Fig. 4 . (Cont inued)

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366 M . - W . F u e t a l . / J o u r n a l o j M a t e r i a l s P r o c e s s i n g T ec h n o lo g y 5 2 ( 1 99 5 ) 3 5 9 3 6 7

a f u r t h e r d i e s et , s u i t a b l e f o r t w i n - d r i v e p r e ss , a n d i t c a n b e u s e d t o p r e s s a u t o m o b i l e

p a r t s . T h e p r e s s u r e m e a s u r e r i s m o u n t e d i n t h e t h r o t t i n g h o l e s .

5 . A p p l i c a t i o n s

T h e w o r k p i e c e s s h o w n i n F i g. 4 a re a p p l i c a t i o n s o f t hi s n e w t e c h n o l o g y t o t h e

m a n u f a c t u r i n g o f a c t u a l w o r k p i e c e s a n d c o m p l i c a t e d p a r ts . A l l o f t h e w o r k p i e c e s h a v e

b e e n m a n u f a c t u r e d i n o n e o p e r a t i o n . W o r k p i e c e s (a ) (c) a r e h e l i c o p t e r p a r ts , (a ) b e i n g

a h e m i s p h e r i c a l p a r t w i t h a b a r r e l b o t t o m . I t s m a t e r i a l i s s t a i n l e s s s t e e l a n d t h e

c o n v e n t i o n a l d r a w i n g c o e f f ic i e n t is 0 .5 6 - 0 . 5 8 , b u t t h e d r a w i n g c o e f f ic i e n t o f i ts b a r r e l

b o t t o m is a b o u t 0 .2 1 . P a r t s o f ( b ) a n d (c ) h a v e a h i g h r e q u i r e m e n t f o r s u r f a c e f in e n e s s

a n d d i m e n s i o n a l a c c u r a c y . T h e w o r k p i e c e s f r o m ( d ) -( l) a re e i t h e r o f c o m p l i c a t e d

s h a p e o r h a v e a s m a l l d r a w i n g c o e f fi c ie n t . T h e d r a w i n g c o e f f ic i e n t o f ( e ) is 0.3 8 , b u t t h e

c o n v e n t i o n a l d r a w i n g c o e ff ic i en t a n d h y d r o - m e c h a n i c a l - d r a w i n g c o e ff ic i en t a r e 0 .5 8

a n d 0 . 4 0 r e s p e c t i v e l y f o r th i s m a t e r i a l . T h e w o r k p i e c e i n (f) h a s t h e p r o p e r t y t h a t t h e

f l a n g e p l a n e i s a t a n a n g l e t o t h e d r a w i n g a x is . T h e d r a w i n g c o e f f ic i e n t ( d e f in e d a s

d/D,

w h e r e d is th e m a x i m u m d i a m e t e r o f t h e w o r k p i e c e a n d D i s t h e o r ig i n a l b l a n k

d i a m e t e r ) is 0. 40 , b u t t h e c o n v e n t i o n a l d r a w i n g c o e f f ic i e n t is 0 . 5 6 - 0 . 5 8 . I t is r e p o r t e d

t h a t t h is k i n d o f w o r k p i e c e w i t h s u c h a d e g r e e o f d e f o r m a t i o n n e e d e i g h t d ie s e ts f o r

d r a w i n g . A l l o f t h e w o r k p e i c e s i n F ig . 4 h a v e b e e n m a n u f a c t u r e d u s i n g t h e s a m e d i e

s e ts , s o t h e n e w p r o c e s s s a v e s a t l e a s t t h i r t y t o f o r t y d ie s e ts t h a t w o u l d b e r e q u i r e d t o

p r o d u c e t h e s e w o r k p i e c e s w i t h c o n v e n t i o n a l t e c h n o l o g y .

6 . C o n c l u s i o n s

(1 ) T h e n e w t e c h n o l o g y o f sh e e t - m e t a l f le x ib l e- d ie f o r m i n g u s in g t h e V P C M h a s

a l o t o f a d v a n t a g e s o v e r o t h e r f l e x ib l e d i e f o r m i n g m e t h o d s , s u c h a s a s m a l l d r a w i n g

c o e f f ic i e n t, g o o d s u r f a c e f i ne n e s s , h i g h d i m e n s i o n a l - a c c u r a c y a n d a s i m p l e a n d g e n -

e r a l - s e r v i c e d i e s t r u c t u r e .

(2 ) T h e n e w t e c h n o l o g y n e e d n o t i m p o s e a n y e x t r a r e q u i r e m e n t s f o r f o r m i n g

e q u i p m e n t o v e r t h o s e f o r c o n v e n t i o n a l d r a w i n g .

(3 ) T h e n e w t e c h n o l o g y h a s a g r e a t e c o m o n i c p o t e n t i a l a n d g r e a t p r o s p e c t s f o r

a p p l i c a t i o n .

( 4 ) T h e V P C M i s s u i t e d t o m a s s p r o d u c t i o n a n d i t s c o s t i s r e a s o n a b l e .

R e f e r e n c e s

[1] Japanese Patent, No. 36-200010.

[2] H. Amino, K. Nakamura. T. Nakagawa, Y. Kurosaki, Y. Mizukusa, Y. Miyake, Hydraulic drawing

and its application on the forming of automobile parts, J. Mats. Proc. Tech. , 23 1990) 243 265.

[3] Japanese Patent, No. 57-55493.

[4] German Patent~ No, 2601423.3.

[.5] Soviet Union Patent, No. 1156774.

[6] S. Thiruvarudchelvan and J.G. Gan, Drawing of hemispheric cups with an annular urethane pad,

J. Mals. Proc. Techn. , 36 1992) 43 55.

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M . - W . F u e t al. / J o u r n a l o f M a t e r i a l s P r o c e s s i n g T e c h n o l o g y 5 2 ( 1 9 95 ) 3 5 9 - 3 6 7 367

[7] S . Th i ruva rudche lv an and J . G . Gan , Deep d raw ing o f con ica l cups us ing f r i c t ion -ac tua ted b lank

ho ld ing ,

J . Mats . Shaping Tech. ,

9 (2) (1991) 59-65.

[8] Y. Kurosaki , I . Fuj ishir , Y. Miyake, Y. Fayukawa, A s imple pier ing process appl icab le to b r i t t le

mater ia ls ,

J. Eng. lnd.

12 (May 1990) 155-160.

[9] Y. Ku rosak i , l . Fuj ishir ., Y. Miy ake, Y. Fa yuk aw a, A piercing techniqu e for g lass sheets by the impac t

com pres s ion o f a v i s cop las ti c p res su re m ed ium ,

J S M E l n t , J . ,

32 (2) (1989) 330 337.

[10] Y. Kuro saki , s tudies on micropla s t ic workin g, Adv . Tech. Plas t ic i ty , 2 (1990) 105% 1064.

[11] Y . Kurosak i , 1 . Fu j i sh i ro , K . Bann and A . Kam oto , A m anufac tu r ing p roces s us ing the im pac t

com press ion of a v iscoplas t ic pressure med ium -appl ic at ion to the pier ing o f f ine holes , J S M E l n t J .,

30, (2621 (1987) 653 660.

[12] M ao-H eng H u an , Shee t m eta l fl ex ib le d ie fo rm ing t echno logy b y us ing the v i scop las t ic p res su re -

ca r ry ing m ed ium .

Proc . 2nd In t . Conf . on Die and Mould Tech. ,

Singapore; (1992) 247-254.