Keynote Paper

Computer Aided Engineering in Body Stamping

A. Takahashi, I. Okamoto; Toyota Motor Corporation/Japan

Sumnary: T h i s paper d e s c r i b e s t h e s tamping CAE system wh ich has been developed t o r a t i o n a l i z e t h e p rocesses o f s tamping d i e des ign , manu fac tu re , t r y o u t and m o d i f i c a t i o n , where t h e most man-hours and l e a d t i m e were r e q u i r e d i n t h e development and p r o d u c t i o n p r e p a r a t i o n o f a c a r body. T h i s system i s c h a r a c t e r i z e d by c a p a b i l i t i e s n o t o n l y t o a l l o w i n t e r a c t i v e and e f f i c i e n t d e s i g n b u t a l s o t o t r a n s m i t t h e d e s i g n i n f o r m a t i o n which can be s u f f i c i e n t l y e v a l u a t e d on t h e same g r a p h i c t e r m i n a l i n terms o f Press f o r m i n g s e v e r i t y , t o t h e subsequent p rocess . T h i s system c o n s t i t u t e s an i m p o r t a n t p a r t o f t h e i n t e g r a t e d body CAD/CAM/CAE system. The e v a l u a t i o n method ernoloved i n t h i s system i s used bv some Jaoanese c a r m a n u f a c t u r e r s as a common methodology. The-changeover f r o m t h e a r t t o t h e Science i s expec ted t o be promoted by r e f i n e m e n t based on f u r t h e r r e s e a r c h and development on s i m u l a t i n g shee t me ta l f o r m i n g and h i g h l y i n t e l l i g e n t CAE.

Key words: CAD, CAM, CAE, Car body, Stamping d i e , E v a l u a t i o n method, Press f o r m i n g s e v e r i t y

1 . INTRODUCTION

I n t h e development o f a new ca r , t h e development o f t h e body and t h e p r o d u c t i o n p r e p a r a t i o n a r e e s s e n t i a l f o r d e t e r m i n i n g t h e l e a d t i m e . O f t h e s e processes, t h e d e s i g n and manu fac tu re o f t h e s tamping d i e s occup ies a g r e a t d e a l o f t h e l e a d t i m e and man hours .

A CAE system f o r s tamping d i e s , t h e r e f o r e , has been developed t o b reak f rom t h e o l d s t a t e p rocess o f t h e p r o d u c t i o n p r e p a r a t i o n and t o r e a l i z e r a t i o n a l i z a t i o n o f a l l processes by c o n n e c t i n g t o g e t h e r t h e e x i s t i n g CAD/CAM s y s t e m s . [ l l

B e f o r e d e v e l o p i n g t h e system, i t was c o n s i d e r e d e s s e n t i a l t h a t t h e system s h o u l d have t h e f u n c t i o n s o f e v a l u a t i n g and m o d i f y i n g t h e d e s i g n so t h a t t h e d e s i g n o f s t a n p i n g d i e s , wh ich l a r g e l y depended on t h e s k i l l o f e x p e r i e n c e d workers, c o u l d be improved t o t h e t e c h n o l o g i c a l l e v e l , and so t h a t t h e accumu la t i on o f t e c h n i c a l knowledge c o u l d be e x p e d i t e d .

I n t h i s paper . some o f T o y o t a ' s concep ts w i l l be d e s c r i b e d by g i v i n g s e v e r a l examples o f p r a c t i c a l a p p l i c a t i o n s o f t h e CAE system and body CAD/CAM systems, t o g e t h e r w i t h o u r e x p e c t a t i o n s i n t h i s a rea f o r f u r t h e r developments.

2. BACKGROUND OF DEVELOPMENT

2.1 Problems o f P r o c e s s i n g and T r a n s m i t t i n g I n f o r m a t i o n on Body Shape

Conven t iona l body development and p r o d u c t i o n p r e p a r a t i o n p rocesses p r i o r t o t h e i n i t i a t i o n o f t h e

0 Style design I I Ca Bodv desisn I 10 Master modell I @I Die design

etch

ze1d

Style drawing 1 I Body drawing I I Master model I I Die drawing -

F i g . 1 C o n v e n t i o n a l Processes o f Car-body Development & P r o d u c t i o n P r e p a r a t i o n

development o f t h e s tamp ing d i e CAE system ( a b o u t 10 yea rs ago ) a r e shown i n F i g . 1 . A t t h e s t y l i n g d e s i g n s tage, c l a y models were p repared a c c o r d i n g t o t h e i d e a ske tches t o p u t t h e d i e d e s i g n e r ' s i d e a s i n t o s p e c i f i c forms. The v e h i c l e e x t e r i o r s t y l i n g i n f o r m a t i o n expressed by t h e c l a y models were c o n v e r t e d i n t o l i f e s i z e e x t e r i o r d raw ings , wh ich were then s e n t t o t h e body d e s i g n p rocess . I n f o r m a t i o n on t h e body s t r u c t u r e was added i n t h i s p rocess , and complex f r e e s u r f a c e s were p u t i n t o t h e l i f e s i z e mas te r body d raw ing . The p r o d u c t i o n p r e p a r a t i o n depar tmen t would read o u t t h e body d raw ing w i t h c o m p l i c a t e d f r e e cu rves . Mas te r models were t h e n p repared f o r i n d i v i d u a l p a r t s . A s i m i l a r r e a d i n g o u t p rocess was repea ted i n t h e s tamping d i e d e s i g n p rocess . The rough geometry o f t h e s tamping d i e s u r f a c e ( d i e f a c e : see F i g . 2 ) was then drawn around t h e s a i d l i n e s . Next , c l a y was a p p l i e d around each mas te r model a c c o r d i n g t o t h e rough drawing, and t h e d e s i g n e r would d e t e r m i n e t h e d i e f a c e shape by c h e c k i n g on necessa ry i t ems . The p l a s t e r models wh ich were rep roduced f r o m t h i s model were used as r e f e r e n c e models i n subsequent p rocesses o f t h e machin ing, f i n i s h i n g and i n s p e c t i o n o f t h e s tamping d i e s . However, a number o f t r y o u t s and d i e f a c e m o d i f i c a t i o n s would have t o be r e p e a t e d a g a i n s t f o r m i n g d e f e c t s and g e o m e t r i c i n a c c u r a c y i n o r d e r t o c r e a t e f i n a l s tamp ing d i e s s u i t a b l e f o r t h e mass p r o d u c t i o n . As d e s c r i b e d so f a r , many d raw ings and models were used as t h e i n f o r m a t i o n media t o exp ress f r e e s u r f a c e s . There fo re , t h e g r e a t m a j o r i t y o f man hours and e f f o r t s i n t h e i n d i v i d u a l p rocesses were spen t f o r t h e t r a n s m i s s i o n and Process ing o f such i n f o r m a t i o n , and f o r t h e s a i d m o d i f i c a t i o n s n e c e s s i t a t e d b y t h e i nadequa te i n t e g r i t y o f i n f o r m a t i o n .

I n o r d e r t o improve t h e p r o d u c t i v i t y i n t h e s e processes, i t was e s s e n t i a l t o b reak o u t o f t h e o u t - d a t e d o p e r a t i n g manner, t o improve t h e i n f o r m a t i o n media, t o i n c r e a s e t h e p r o c e s s i n g speed and t h e e f f i c i e n c y o f t h e i n f o r m a t i o n t r a n s m i s s i o n . I n t h i s rega rd . t h e i n t r o d u c t i o n o f CAD/CAM systems and t h e i r i n t e g r a t i o n t h r o u g h o u t t h e p rocesses f r o m t h e s t y 1 i n g d e s i g n t o t h e s tamp ing d i e manufacture were c o n s i d e r e d as t h e optimum measures. The NC p r o c e s s i n g system f o r s tamp ing d i e s was p u t i n t o p r a c t i c a l a p p l i c a t i o n s i n many y e a r s ago a t Toyota, wh ich was f o l l o w e d by t h e i n t r o d u c t i o n o f CAD systems f o r s t y l i n g d e s i g n and body s t r u c t u r e des ign . T h e r e f o r , Toyota was ready t o complete an i n t e g r a t e d system if n u m e r i c a l d a t a o f d i e face c o u l d be a t t a i n e d .

Annals of the ClRP Vol. 37/2/1988 569

2.2 Problems o f P ress Fo rm ing Techno log ies

The d i e f a c e c o n t a i n i n g t h e b l a n k h o l d e r su r face , s t e p draw and draw bead as shown i n F i g 2 . i s t h e most i m p o r t a n t f a c t o r f o r s u c c e s s f u l p r e s s f o r m i n g . I n p a s t , however, o n l y rough ske tches o f t h e shapes were showr i n d raw ings a t t h e d e s i g n s tage, wh ich were a l s o i nadequa te f o r t h e e v a l u a t i o n o f f o r m i n g t e c h n o l o g y . Ir o r d e r t o compensate f o r t h e inadequacy, t h e d e s i g n e r had t o be i n v o l v e d i n t h e c r e a t i o n work o f t h e d i e face shape around t h e mas te r model . The d e s i g n e r t h e n gave d e t a i l e d i n s t r u c t i o n s t o c r e a t e smooth b l a n k h o l d e r s u r f a c e s and c o m p l i c a t e d s t e p draws. The f i n a l shapes were t h e n determined, i n c o r p o r a t l n g p r o p e r Judgments based on t h e e x p e r i e n c e and s k i l l i n t r y o u t o p e r a t i o n s .

I n t h e t r y o u t s tage, however, s u r f a c e d e f l e c t i o n s , w r i n k l e s , f r a c t u r e s and o t h e r f o r m i n g d e f e c t s as w e l l as g e o m e t r i c i n a c c u r a c y t h a t wou ld i m p a i r t h e body f i t t i n g q u a l i t y n o r m a l l y o c c u r r e d . Such problems were p r i m a r i l y a t t r i b u t a b l e t o t h e i nadequa te d i e f a c e t e c h n o l o g y . Thus c o r r e c t i o n c y c l e s , such as f u r t h e r d i e f a c e m o d i f i c a t i o n s and t r y o u t s , had t o be repea ted o v e r and o v e r again, wh ich c o n s t i t u t e d t h e b o t t l e n e c k a g a i n s t t h e smooth and q u i c k p r e p a r a t i o n work f o r t h e body p r o d u c t i o n . If outcomes o f such e f f o r t s were S t i l l

inadequate, s w i t c h i n g o v e r t o a h i g h e r g rade m a t e r i a l was sometimes done even i f i t would i n c r e a s e t h e c o s t . L i kew ise , chang ing t h e p r o d u c t shape i t s e l f was done i n some case, even though t h e m a t e r i a l y i e l d r a t e c o u l d be p e n a l i z e d and t h e d e s i g n i n t e n t i o n m i g h t be i m p a i r e d . ( F i g . 3 )

A c t i v e e x p e r i m e n t a l a n a l y s i s on f o r m i n g d e f e c t s have been c a r r i e d o u t t o f i n d a p p r o p r i a t e measures a g a i n s t t h e dependency on t h e s k i l l o f exper ienced t e c h n i c i a n s . As a r e s u l t , common r e c o g n i t i o n s o f v a r i o u s phenomena, t h a t would cause such d e f e c t s i n p r e s s f o r m i n g p rocesses , have been e s t a b l i s h e d . [ 6 . 7 , 8 1 I n o r d e r t o a t t a i n r e a l t e c h n o l o g i c a l advancements i n t h e s e r i e s o f p rocesses s t a r t i n g f r o m t h e s tamp ing d i e d e s i g n t o t h e t r y o u t and m o d i f i c a t i o n s tage, f u r t h e r developments o f t h e ex p o s t f a c t o measures d e s c r i b e d above, t h e e v a l u a t i o n o f t h e d i e f a c e shape i n te rms o f f o r m i n g s e v e r i t y i n t h e e a r l y s tage o f d i e f a c e d e s i g n - t h a t i s . p r i o r t o t h e d i e m a n u f a c t u r i n g - and t h e e s t a b l i shment o f measures t o upgrade t h e i n t e g r i t Y o f t h e d e s i g n b e f o r e send ing such i n f o r m a t i o n t o subsequent processes were v i t a l . On development o f t h i s CAE system, t h e r e f o r e , t h e i n c o r p o r a t i o n o f means t o p r o v i d e a c o n c r e t e fo rm f o r t h i s f u n c t i o n ( p r e s s f o r m i n g s e v e r i t y e v a l u a t i o n f u n c t i o n ) was c o n s i d e r e d as t h e most e s s e n t i a l p o i n t .

3 . BASIC CONCEPTS FOR DEVELOPMENT

It was c o n s i d e r e d t h a t f o l l o w i n g two r e q u i r e m e n t s s h o u l d be met i n t h e development o f t h e s tamping CAE system.

( 1 ) C a p a b i l i t i e s t o a l l o w e f f i c i e n t i n t e r a c t i v e d e s i g n s and t h e use o f d e s i g n r e s u l t s i n t h e d i e manu fac tu re CAM s h o u l d be p r o v i d e d . F o r t h i s r e q u i r e m e n t t h e system shou ld be focused m a i n l y or- t h r e e d imens iona l f r e e c u r v e s and s u r f a c e s .

Die face

Die structure Blankholder surface

., , ,’ ”

F i g . 2 Components o f Stamping D i e

t Die face design td SExoerience B Art I L 1 . c SRelerence to similar panels in past

Modification

Style design change

F i g . 3 Conven t iona l T r y o u t Process f o r E l i m i n a t i n g D e f e c t s

( 2 ) C a p a b i l i t i e s t o e v a l u a t e t h e f o r m i n g s e v e r i t y s u c c e s s i v e l y on t h e same g r a p h i c t e r m i n a l s h o u l d be a l s o g i v e n . I n t h i s rega rd , f u n c t i o n s t o ana lyze and s i m u l a t e p ress f o r m i n g phenomena a r e necessary.

The use o f FEM was c o n s i d e r e d f i r s t . b u t i t was dec ided n o t t o use i t S ince even a r e l a t i v e l y s i m p l e p rob lem r e q u i r e d an enormous amount o f c a l c u l a t i o n t i m e a t t h a t t i m e , and f u r t h e r r e s e a r c h and development f o r many y e a r s appeared t o be necessa ry . Thus, i t was dec ided t o b reak down phenomena t h a t would o c c u r i n f o r m i n g p rocesses i n t o segments and t o S i m p l i f y them d r a s t i c a l l y , t hen t o deve lop a p r o p e r a n a l y t i c a l method f o r each segment. It was a l s o c o n s i d e r e d t h a t such an a n a l y t i c a l method s h o u l d n o t c o n s t i t u t e a b l a c k box f o r d e s i g n e r s . The o u t p u t i n f o r m a t i o n f rom t h e system s h o u l d be easy f o r d e s i g n e r s t o unders tand w h i l e c o r r e s p o n d i n g t o e m p i r i c a l r u l e s . Acco rd ing t o such concep ts , i t was dec ided n o t t o Pursue t h e c a p a b i l i t y t o p r o v i d e oDtimum s o l u t i o n , b u t t o be c o n t e n t w i t h t h e system as l o n g as i t would p l a y t h e a s s i s t i v e r o l e i r - f i n d i n g r e l a t i v e l y good s o l u t i o n s . To pay p r o p e r a t t e n t i o n t o t h e a n a l y t i c a l f u n c t i o n , so t h a t i t would become capab le o f i n c o r p o r a t i n g improvements and a d d i t i o n s a c c o r d i n g t o new knowledge and i n f o r m a t i o n , was a l s o c o n s i d e r e d v i t a l . Based on t h e s e concepts, t h e s tamp ing CAE system which i s s o - c a l l e d as D i e Face CAD, has been deve loped . [2 ,41

570

4 . FUNCTIONS OF THE STAMPING CAE

4.1 Geomet r i ca l F u n c t i o n s

Power fu l g e o m e t r i c a l f u n c t i o n s a r e necessary t o o b t a i n a p p r o p r i a t e g e o m e t r i c a l i n f o r m a t i o n f o r t h e e v a l u a t i o n o f t h e f o r m i n g s e v e r i t y , t o a l l o w e f f i c i e n t i n t e r a c t i v e des igns o f d i e f a c e s and t o t r a n s m i t g e o m e t r i c a l d a t a t o t h e CAM system f o r t h e s tamping d i e m a n u f a c t u r i n g Process. Hosaka 's formula was employed as t h e f o r m u l a t o exp ress c u r v e s and s u r f a c e s , because o f i t s s i m p l e f o r m and a f f l u e n t e x p r e s s i o n c a p a b i l i t y . [3,9] T y p i c a l examples o f g e o m e t r i c a l f u n c t i o n s u s i n g t h i s f o r m u l a a r e shown i n F i g . 4 . The f u n c t i o n A, f o r example, a l l o w s dynamic c o r r e c t i o n s o f t h r e e d imens iona l c u r v e s on g r a p h i c t e r m i n a l s . F u n c t i o n s G and H a l l o w e f f i c i e n t c r e a t i o n s o f cu rves , w h i l e f u n c t i o n s K and L a r e o f t e n used f o r t h e e v a l u a t i o n o f f o r m i n g s e v e r i t y . The f u n c t i o n K t o measure t h e d i s t a n c e between two su r faces , and t h e f u n c t i o n L t o measure enve lop c u r v e s a r e b a s i c f u n c t i o n s f o r t h e d e t e r m i n a t i o n o f Punch c o n t a c t i n g area, and f o r t h e d e t e r m i n a t i o n o f shape change o f s e c t i o n l i n e s , r e s p e c t i v e l y , as w i l l be d e s c r i b e d l a t e r .

4.2 E v a l u a t i o n Methods o f P ress Forming S e v e r i t y

B e f o r e d e v e l o p i n g t h e methods, t h e r e l a t i o n s h i p between t h e p r e s s f o r m i n g d e f e c t s and t h e a n a l y t i c a l means u s i n g CAE a r e summarized i n F i g . 5 . F i r s t , t h e p r e s s f o r m i n g d e f e c t s a r e d i v i d e d i n t o two groups. One g roup c o n s i s t s o f g e o m e t r i c a l s u r f a c e d e f e c t s such as s u r f a c e d e f l e c t i o n and w r i n k l e . t h e o t h e r i s f r a c t u r e . The causes o f i n s u f f i c i e n t g e o m e t r i c a l s u r f a c e d e f e c t s a r e c a t e g o r i z e d f rom ( 1 ) t o ( 6 ) i n t e rms o f phenomena o c c u r r i n g i n p r e s s f o r m i n g p rocesses . Three c a t e g o r i e s o f f r a c t u r e f rom ( 7 ) t o ( 9 ) a r e i d e n t i f i e d .

Blank-holding

Punch contact

Counter die forming

Taking off

F i g . 4 Examples o f Geomet r i ca l F u n c t i o n s

The a n a l y t i c a l means of t h e p r e s s f o r m i n g d e f e c t s have been p lanned f o r development t o e s t i m a t e t h e d e f o r m i n g b e h a v i o r s o f t h e shee t d u r i n g p r e s s f o r m i n g p rocesses . Geomet r i ca l f u n c t i o n s f o r cu rved l i n e s and s u r f a c e s necessa ry t o d e s i g n d i e faces a r e used f o r c o n c r e t e means from ( a ) t o ( e ) f o r e v a l u a t i n g t h e whole p r e s s fo rm ing s e v e r i t y . However f o r means ( a ) a l i n e a r FEM can a l s o be employed. F o r means ( f ) , ( 9 1 and ( h ) a s i m p l i f i e d p l a s t i c i t y calculation t o e v a l u a t e t h e l o c a l p r e s s fo rm ing s e v e r i t y i s added t o t h e g e o m e t r i c a l ones t o r a i s e e v a l u a t i o n accu racy .

The e v a l u a t i o n f u n c t i o n s o f Dress f o r m i n g s e v e r i t y deve loped w i t h p r e v i o u s l y ment ioned concep t a r e shown i n F i s . 6 . The c h a r a c t e r i s t i c s o f t h e s e f u n c t i o n s a r e s i m p l i f i e d s i m u l a t i o n o f t h e p r e s s f o r m i n g p rocesses i n a f o r m easy t o comprehend, and t h e r e s u l t s o f t h e c a l c u l a t i o n s can be used as a s s i s t i v e i n f o r m a t i o n t o Judge t h e q u a l i t y o f t h e d e s i g n and t o examine i t d u r i n g i n t e r a c t i v e d e s i g n i n g .

F i g . 5 P ress Forming D e f e c t s and A n a l y t i c a l Means Us ing CAE

57 1

( a ) B l a n k shape i n d i e c a v i t y To p r e d i c t b l a n k shape i n t h e d i e c a v i t y , a l i n e a r

FEM f u n c t i o n c a p a b i l i t y f o r s t e e l shee t bend ing i s b u i 1 t - 1 n.

( b l Spread ing b e h a v i o r o f punch c o n t a c t a rea The d r a w i n g d e p t h i s c a l c u l a t e d f o r t h e whole a rea

o f t h e d i e c a v i t y and t h i s d iag ram i s expressed as a c o n t o u r map a f t e r t h e c a l c u l a t i o n . W i t h t h i s diagram, t h e s p r e a d i n g b e h a v i o r o f Punch c o n t a c t a rea t o t h e shee t can be e s t i m a t e d d u r i n g t h e f o r m i n g processes.

( c ) Shape change o f s e c t i o n l i n e s The s e c t i o n l i n e s o f a shee t a r e f i g u r e - p r o c e s s e d

when t h e y a r e deformed w i t h t h e punch and d i e . W i t h t h i s d iag ram t h e shee t d e f o r m a t i o n can be e s t i m a t e d a p p r o x i m a t e l y d u r i n g t h e f o r m i n g p rocesses .

( d ) G e n e r a t i n g b e h a v i o r o f r i d g e l i n e s

t h e r i d g e l i n e s o c c u r s d u r i n g t h e f o r m i n g p rocesses . T h i s a l l o w s us t o e s t i m a t e how t h e g e n e r a t i o n o f

( e ) Mean s e c t i o n l e n g t h r a t i o T h i s i s e q u i v a l e n t t o t h e average e l o n g a t i o n o f

t h e pane l . It i s assumed t h a t l a r g e d i f f e r e n c e s i n t h e mean e l o n g a t i o n r a t i o between n e i g h b o r i n g s e c t i o n s l e a d t o n o n - u n i f o r m fo rm ing .

( f ) Loca l e l o n g a t i o n r a t i o [ l 0 , l l l T h i s i s f o r f i n d i n g t h e l o c a l e l o n g a t i o n r a t i o

when t h e shee t i s deformed w i t h b o t h t h e punch and d i e . I n t h i s c a l c u l a t i o n , t h e shee t movement ( A I ) and t h e succeed7ng change o f s t r a i n ( E a . E b ) a r e o b t a i n e d so t h a t t h e r e s i s t i n g f o r c e ( F r ) between t h e shee t and d i e may be ba lanced w i t h t h e s t r e s s e s ( F a , F b ) o f t h e shee t a t b o t h s i d e s o f t h e c o n t a c t a rea .

( 9 ) Movement o f shee t T h i s can s i m u l a t e a p p r o x i m a t e l y t h e rnoverrlent o f

t h e l i n e s drawn on t h e shee t , t h a t is, t h e movement of t h e shee t d u r i n g p r e s s f o r m i n g p rocesses .

/' on die lace llank holder ~ u r l a c e

a i Blank shape in die cavity

c Shape change of section lines

8" dle cavity

(e) Mean section length ratio

Sheet edge

-Amaunl of movement-

(g) Movement of sheet

die cavity

b Spreading behavior of punch contact area

'd Generating behavior of ridge lines

' f ! Local elongation ratio

E + E , + E , = O

h Stretchlshrink flange behavior

F ig .6 E v a l u a t i o n F u n c t i o n s f o r Press Forming S e v e r i t y

( h ) S t r e t c h / s h r i n k f l a n g e b e h a v i o r [ l 2 ] T h i s i s f o r t h e d e t e r m i n a t i o n o f s t r e t c h / s h r i n k

f l a n g e b e h a v i o r b y s i m p l i f i e d p l a S t i c ? t y a n a l y s i s . Us ing e x p e r i m e n t a l d a t a on t h e m a t e r i a l f l o w d i r e c t i o n which depends on t h e geometry o f t h e P roduc t and p r e s s f o r m i n g c o n d i t i o n s , w i t h d a t a on t h e s t r a i n d i s t r i b u t i o n o f t h e s t r e t c h e d f l a n g e , s t r a i n s o f m i n u t e e lements i n t h r e e d i r e c t i o n s can be c a l c u l a t e d a c c o r d i n g t o t h e volume cons tancy .

F i g . 7 Process o f D i e Face Des ign U s i n g CAE

572

5 . DIE FACE DESIGN PROCEDURE USING THE STAMPING CAE

The p rocess o f t h e d i e f a c e d e s i g n u s i n g t h e s tamp ing CAE system i s shown i n F i g . 7 . F i r s t , t h e d a t a o f a pane l i s e x t r a c t e d f rom t h e d a t a base made by t h e o t h e r CAD systems f o r t h e d e s i g n o f t h e s t y l e and body s t r u c t u r e , and i t i s i n p u t i n t o t h i s system. Next, t h e d i e f a c e s ( t h e s t e p draw, b l a n k h o l d e r s u r f a c e , and draw bead) a r e des igned i n t e r a c t i v e l y on t h e g r a p h i c t e r m i n a l , f o l l o w e d by t h e e v a l u a t i o n s o f p r e s s f o r m i n g s e v e r i t y f o r a h i g h e r l e v e l o f d e s i g n . Based on t h i s r e s u l t , t h e b l a n k shapes a r e determined, t h e n t h e d e s i g n o f t h e d i e f a c e s i s completed as shown i n P h o t o l . Here, t h e shapes o f t h e d i e f a c e s a r e S t o r e d i n t h e d a t a base as a numer i ca l model c o n t a i n i n g cu rved s u r f a c e i n f o r m a t i o n . Thus t h e d e t a i l e d shape can be checked e a s i l y as shown i n P h o t o l ( b 1 . I n t h e c o n v e n t i o n a l procedure, many models were r e q u i r e d t o examine t h e shape o f t h e d i e f a c e s and t o manu fac tu re t h e s tamping d i e s . W i t h t h i s CAE system, however, v a r i o u s k i n d s o f t o o l i n g models can be a b o l i s h e d s i f l ce t h e d a t a o f t h e d i e f a c e s i s t r a n s m i t t e d d i r e c t l y t o t h e CAM system f o r t h e manu fac tu re o f t h e s tamping

d i e s . Thus i t was p o s s i b l e t o g r e a t l y r a t i o n a l i z e t h e ( b ) D e t a i l d i e m a n u f a c t u r i n g p rocess .

P h o t o l Complete Shape o f D i e Face

6. APPLICATIONS OF THE EVALUATIONS FOR PRESS FORMING SEVERITY s p e c i f i c problems i n o t h e r e v a l u a t i o n s . Consequen t l y

t h e g e n e r a t i o n o f s u r f a c e d e f l e c t i o n s was minima7 a t 6 . 1 Spread ing B e h a v i o r o f Punch C o n t a c t Area t h e i n i t i a l Stage o f t h e t r y o u t . Here, i t i s e s t i m a t e d

t h a t a p p r o x i m a t e l y 300 man hours were saved a t t h e t r y o u t and m o d i f i c a t i o n s t a g e s . F19.8 shows an example of t h i s f u n c t i o n a p p l i e d t o

t h e d i e f a c e d e s i g n o f a q u a r t e r pane l . I n t h i s case, s u r f a c e d e f l e c t i o n t e n d s t o o c c u r a t t h e c o r n e r o f t h e window when f o r m i n g t h e window.

6.2 Mean S e c t i o n Leng th R a t i o

Exper ience shows t h a t t h e e a r l i e s t P o s s i b l e The p i l l a r base o f a q u a r t e r pane l f o r a n o t c h c o n t a c t o f t h e punch a t t h e c o r n e r i s e f f i c i e n t i n

Sack s t y l e c a r i s i n t h e shape o f a saddle, wh ich r e s t r a i n i n g t h e w r i n k l e l i k e l y t o occu r when f o r m i n g

r e s u l t s i n n o n - u n i f o r m f o r m i n g . There fo re , s u r f a c e t h e window by t h e l o w e r d i e . The re fo re , d i e f a c e d e s i g n

d e f l e c t i o n tends t o o c c u r a t t h i s p o r t i o n . It i s v i t a l A and were and a contour map was Obtained t o check on t h e mean s e c t i o n l e n g t h r a t i o as w e l l as f o r each. Des ign A was s i m i l a r t o t h e c o n v e n t i o n a l d i e

t h e sp read ing b e h a v i o r o f t h e punch c o n t a c t a rea t o f a c e . On t h e o t h e r hand, i t was d e t e r m i n e d t h a t d e s i g n

a v o i d t h e s u r f a c e d e f l e c t i o n . F i g . 9 shows processed led to ear'ier punch 'Ontact at the window corner d a t a o f t h e f o r m a b i l i t y e v a l u a t i o n a c c o r d i n g t o mean

t h a n d e s i g n A, and B was more e f f e c t i v e i n r e s t r a i n i n g s e c t i o n l e n g t h r a t i o i n t e n k i n d s o f q u a r t e r p a n e l s ( A -

the S . ~ ~ ~ ~ ~ ~ deflection than A m Design ' w a s adopted J ) of r e c e n t models . Maximum v a l u e s o f t h e s a i d r a t i o here for the stamping die because lt had no a r e p l o t t e d on t h e h o r i z o n t a l a x i s , w h i l e g r a d i e n t s o f

F i g . 8 A p p l i c a t i o n o f "Sp read ing B e h a v i o r of Punch C o n t a c t Area" f o r A v o i d i n g S u r f a c e D e f l e c t i o n F i g . 9 C r i t e r i a o f S u r f a c e D e f l e c t i o n i n

Q u a r t e r Panel by "Mean S e c t i o n Leng th R a t i o "

573

t h o s e r a t i o s i n n e i g h b o r i n g a reas a r e p l o t t e d on t h e v e r t i c a l a x i s . I n t h e f i g u r e , amounts o f t r y o u t man h o u r s spen t r e s p e c t i v e l y a r e c l a s s i f i e d i n t o f o u r s tages which a r e expressed by t h e i r symbols. Owing t o such e f f o r t s , c r i t e r i a f o r t h e p r e v e n t i o n o f s u r f a c e d e f l e c t i o n have been e s t a b l i s h e d . Eve r s i n c e t h e a p p l i c a t i o n o f c r i t e r i a , a p p r o x i m a t e l y 200 man hours on ave rage have been reduced. The q u a n t i t a t i v e P rocess in9 o f knowledge accumulated by i n d i v i d u a l d e s i g n e r s 1s a l s o a l l o w e d by t h e e v a l u a t i o n f u n c t i o n f o r p r e s s f o r m i n g s e v e r i t y , as ev idenced by t h i s example. It i s expec ted t h a t p r o g r e s s i n p r e s s f o r m i n g t e c h n o l o g y w i l l be a c c e l e r a t e d by t h e accumu la t i on o f such da ta .

Design process

6 . 4 D e t e r m i n a t i o n o f T r i m n i n g P o s i t i o n

Verification

The c o n v e n t i o n a l methods tend t o cause more e r r o r s than t h i s system which a l l o w s t h e d e t e r m i n a t i o n o f t r i m m i n g p o s i t i o n w i t h ease and h i g h e r accuracy, by u s i n g t h e s a i d f u n c t i o n o f s t r e t c h l s h r i n k f l a n g e Sehav io rs ( h ) . A compar ison was made by s e t t i n g t h e r i g h t end o f a f e n d e r o f a c e r t a i n c a r by t h e c o n v e n t i o n a l method. w h i l e s e t t i n g t h e l e f t end by t h i s f u n c t i o n . The l a t t e r p r o v i d e d f a v o r a b l e r e s u l t s w i t h fewer d e v i a t i o n s as soown i n F ig .11 . Thus a r e d u c t i o n of man hours r e q u i r e d f o r c o r r e c t i o n s o f e r r o r s 3 t t r i b u t e d t o i n s u f f i c i e n t accu racy i n des ign has been a l l o w e d by t h e a m l i c a t i o r o f t h i s system.

6.3 Local E l o n g a t i o n Ra t io 7. THE STATUS OF BODY CAD/CAM/CAE AT TOYOTA

F i g . 1 0 shows an example o f a d i e f a c e d e s i g n where f r a c t u r e i s avo ided as much as p o s s i b l e and t h e y i e l d r a t e i s maximized. I n t h e f i r s t s t a g e ( 1 ) , a c o n v e n t i o n a l d i e f a c e was used, where t h e l o c a l e l o n g a t i o n r a t i o has t o o much a l l owance a g a i n s t t h e d e f o r m i n g l i m i t . I n t h e second s tage (2). t h e d i e f a c e was e l i m i n a t e d by 10mm t o save m a t e r i a l , where t h e r a t i o exceeded t h e d e f o r m i n g l i m i t . Then i n t h e t h i r d s tage ( 3 ) . t h e r a d i u s o f t h e s t e p draw was m o d i f i e d , where t h e s t r a i n was m a i n t a i n e d 7% below t h e l i m i t . To v e r i f y t h i s , t h e s t r a i n o f t h e panel formed b y t h e o p t i m i z e d d i e f a c e ( 3 ) was measured. It was proven t h a t t h e d i f f e r e n c e between t h e c a l c u l a t e d and measured v a l u e s was l e s s t h a n 2% wh ich was p r e c i s e enough t o be used i n a c t u a l d e s i g n . I n t h i s case 1% m a t e r i a l was saved because l O m m was e l i m i n a t e d o u t o f t h e t o t a l l e n g t h o f 1,000mm.

I

I

F i g . 1 0 A p p l i c a t i o n o f "Loca l E l o n g a t i o n R a t i o " t o A v o i d F r a c t u r e and Improve Y i e l d Rate

I Method I Accuracy I

CAE

Volume constancy a 3 I I D 1 2 3 4 m m

F i g . 1 1 A p p l i c a t i o n o f " S t r e t c h / S h r i n k B e h a v i o r " t o De te rm ine t h e Trimming P o s i t i o n

574

The stamping CAE system d e s c r i b e d so f a r c o n s t i t u t e s p a r t o f body CAD/CAM/CAE systems o f Toyota. E f f i c i e n c i e s o f a l l p rocesses f rom t h e s t y l i n g d e s i g n t o t h e s tamping d i e m a n u f a c t u r i n g have been marked ly improved, as d a t a base c r e a t e d by t h e s e systems can be t r a n s f e r r e d and i n t e r a c t e d f r e e l y among themselves. The f o l l o w i n g g i v e s f e a t u r e s o f i n d i v i d u a l s y s t e m s . ~ l 3 , 1 4 ]

A t t h e s t y l i n g d e s i g n p rocess , where i t bas been s a i d d i f f i c u l t t o s u p p o r t c r e a t i v e a c t i v i t i e s by CAD, ve have nade i t P o s s i b l e t o m o d i f y shapes i n t e r a c t i v e l y on t h e g r a p h i c t e r m i n a l a s though on a c l a y mode1.[15,16.17,181 These f u n c t i o n s enab le us t o check many p r o p o s a l s f o r s t y l i n g i n a s h o r t P e r i o d and t o g e t v e r y good d e s i g n q u a l i t y . As f o r t h e o u t p u t f o r succeeding processes, a complete geomet r i c model i s D rov ided , which c o n t a i n s v e r y s u b t l y expressed s u r f a c e s such as c o m p l i c a t e d f i l l e t s . T h i s system has t h e f u n c t i o n s t o e v a l u a t e f i n i s h e d s u r f a c e s f rom t h e a e s t h e t i c p o i n t o f v iew . F i g . 1 2 shows an example, wh ich i n d i c a t e s t h a t t h e smooth f l o w o f t h e e n t i r e s u r f a c e can be checked by d i s p l a y i n g h i g h - l i g h t l i n e s . The smoothness o f s J r f a c e can be a l s o checked by d i s p l a y i n g t h e c u r v a t u r e d i s t r i b u t i o n a l o n g p r i n c i p a l cu rves , as shown i n F ig .13 .

F i g . 1 2 S i m u l a t i o n o f H i g h l i g h t L i n e

F i g . 1 3 C u r v a t u r e D i s t r i b u t i o n a l o n g P r i n c i p a l Curves

A t t h e body s t r u c t u r a l d e s i g n p rocess , a l l body p a r t s a r e des igned i n t e r a c t i v e l y on g r a p h i c t e r m i n a l s i n s t e a d o f c o n v e n t i o n a l d r a f t i n g boards and r e p r e s e n t e d as t h r e e d imens iona l w i r e f rame d a t a on a d a t a base. The s u p p o r t system i s named CADETT.Ll91 The body O u t e r shape d a t a t o be r e c e i v e d by t h i s system i s t h e d a t a c r e a t e d by S t y l e CAD mentioned e a r l i e r . F i g . 1 4 shows an example of a r e a r doo r Danel. We have t a k e n i n t o c o n s i d e r a t i o n t h a t t h e system s u p p o r t s q u i c k response. ease o f use and a p p l i c a t i o n f u n c t i o n s such a5 s t a n d a r d i z e d o p e r a t i o n t o improve d e s i g n p r o d u c t i v i t y .

As d e s c r i b e d i n t h e f o r e g o i n g , t h e stamDing d i e manu fac tu re i s i n i t i a t e d by comb in lng t h e d a t a c r e a t e d by S t y l e CAD, CADETT and D i e Face CAD. The s u p p o r t system named TINCA has f o l l o w i n g fea tu res . [20 ,21 .22 ,231

( 1 ) Au tomat i c g e n e r a t i o n o f f i l l e t s u r f a c e s w i th a method based on s e q u e n t i a l ~ r o c e s s i n g and p a t t e r n r e c o g n i t i o n . S p e e d i l y and h i g h l y r e l i a b l e c a l c u l a t i o n o f c u t t e r p a t h s by o f f s e t t i n g b i - l i n e a r pa tches as an a p p r o x i m a t i o n t o s u r f a c e s .

( 2 ) Free m i l l i n g d i r e c t i o n s u i t a b l e f o r d i e shapes and t h e use o f t a p e r b a l l end m i l l and f l a t end m i l l .

( 3 ) AdJustment o f t h e c l e a r a n c e between punch and d i e by m o d i f y i n g t h e c u t t e r p a t h s and f i n i s h i n g d i e s u s i n g 3-D measur ing machine.

F19.14 Master Drawing o f Rear Door I n n e r

F ig .15 shows t h e numer i ca l model c r e a t e d by TINCA f o r t h e r e a r doo r i n n e r pane l . i t i s found f rom t h i s f i g u r e t h a t t h e f i l l e t s u r f a c e s a r e c o m p l e t e l y expressed. A d i e SubJeCted t o t h e NC p r o c e s s l n g i s measured by t h e o n - l i n e 3-D measur ing machine, t h e n d e v i a t i o n s f rom t h e d a t a base a r e d i s p l a y e d . L o c a t i o n s and amounts o f such d e v i a t i o n s a r e a l s o marked by d r i l l i n g them a c c u r a t e l y on t h e d i e s u r f a c e i t s e l f . The f i n i s h i n g o f t h e d i e s u r f a c e i s pe r fo rmed u s i n g such i n f o r m a t i o n . Photo.2 i l l u s t r a t e s how i t i s done. The adJustment o f t h e c l e a r a n c e between t h e punch and d i e i s necessary t o suppress s u r f a c e d e f l e c t i o n s . I n t h i s system, t h e measured punch(ma1e d i e ) s u r f a c e d a t a can be t r a n s f o r m e d by t a k i n g accoun t o f t h e shee t t h i c k n e s s and t h e n e c e s s i t a t e d b o t t o m i n g Pressu re d i s t r i b u t i o n t o t h e fema le d i e s u r f a c e d a t a .

F ig .15 Numer i ca l Model o f Rear Door I n n e r

t =0.7 II =(-0.15-0.3)1

F ig .16 C lea rance D i s t r i b u t i o n o f Q u a r t e r Panel Draw D i e

Photo2 Computer A ided F i n i s h i n g System

575

F i g . 1 6 shows t h e c l e a r a n c e d i s t r i b u t i o n o f a q u a r t e r pane l draw d i e o b t a i n e d i n t h i s manner. Owing t o t h e h i g h l y p r e c i s e f i n i s h i n g ach ieved by v e r y a c c u r a t e s u r f a c e c a l c u l a t i o n s t a k i n g accoun t o f even t h e s l i g h t e s t c l e a r a n c e d i s t r i b u t i o n , and t h e feed -back o f measured da ta , t h e d i e m a n u f a c t u r i n g t i m e i s reduced remarkab ly and accu racy o f d i e s a r e much improved.

A f t e r t h e f i r s t p r a c t i c a l a p p l i c a t i o n o f t h e s tamping CAE system i n 1981, t h e s e systems s t a r t e d f u n c t i o n i n g as an i n t e g r a t e d t o t a l system, and f u r t h e r development and improvement e f f o r t s have been added t o a t t a i n t h e p r e s e n t system. F a v o r a b l e e f f e c t s b r o u g h t abou t i n p a s t 5 yea rs by t h e s tamping CAE system a r e as f o l 1 ows.

The d i e d e s i g n speed has been a c c e l e r a t e d by p o w e r f u l g e o m e t r i c a l f u n c t i o n s and t h e f u n c t i o n t o e v a l u a t e t h e p r e s s f o r m i n g s e v e r i t y ment ioned i n t h e f o r e g o i n g r e s u l t e d i n a 50% r e d u c t i o n i n man-hours by t h e e l i m i n a t i o n o f p rocesses r e q u i r e d i n p a s t . On manu fac tu re o f d i e faces , t h e man-hour i s a l s o reduced by 30% owing t o t h e e l i m i n a t i o n o f measur ing work r e q u i r e d f o r t h e f a b r i c a t i o n o f models and t h e p r e p a r a t i o n o f NC p r o c e s s i n g d a t a . I n t r y o u t and m o d i f i c a t i o n work, t h e man-hour i s reduced b y 30% by u p g r a d i n g t h e e v a l u a t i o n f u n c t i o n o f p r e s s f o r m i n g s e v e r i t y a c c u m u l a t i o n o f t e c h n i c a l know-how, improveven t i n d e s i g n accu racy and u p g r a d i n g t h e p r e s s d i e accu racy . These have r e s u l t e d f r o m t h e cu rved s u r f a c e p r o c e s s i n g by means o f CAM.(Fig.17)

Moreover, t h e t o t a l CAD/CAM system f o r t h e body development p rocess has beer r e a l i z e d by t h e c o m p l e t i o n o f D i e Face CAD, and t o t a l m e r i t s have been implemented t o t h e f u l l e s t e x t e n t . As t h e o v e r a l l r e s u l t o f t h e f o r e g o i n g b e n e f i t s , t h e l e a d t i m e r e q u i r e d f o r t h e d i e d e s i g n and m a n u f a c t u r i n g i s reduced by 2 5 % . ( F i g . 1 8 )

100

50

'81 '86 '81 '86 '81 '86

Fig.17 Man hour Reduc t ion by "D ie Face CAD"

-100 -50 - 0

~ Die Design Completion 01 pgHfz4 Die Manufacturing Stamping Dies

'81 r------I

F i g . 1 8 Lead Time Reduc t ion by "Die-Face CAD"

8. EXPECTATIONS FOR FUTURE

The concep t o f t h e i d e a l i n t e g r a t e d CAD/CAM/CAE system conce ived by t h e a u t h o r s i s shown i n F ig .19. It i s i m p o r t a n t t o p r o v i d e t h e CAD/CAM/CAE system f o r each p rocess w i t h c a p a b i l i t i e s t o c a r r y o u t n o t o n l y t h e e f f e c t i v e g r a p h i c p r o c e s s i n g b u t a l s o t o Suppor t r e s p e c t i v e e n g i n e e r i n g a c t i v i t i e s t h r o u g h i t s i n t e l l i g e n t f u n c t i o n s . Moreover, i t i s a l s o v i t a l t o s y s t e m a t i z e t e c h n i c a l i n f o r m a t i o n o b t a i n e d f rom t h e e n g i n e e r i n g a c t i v i t i e s and t o i n c o r p o r a t e t h e i n f o r m a t i o n i n a new d a t a base so t h a t i t may be used i n subsequent p r o j e c t s . [ 2 4 1

The e v a l u a t i o n method o f p r e s s f o r m i n g s e v e r i t y d e s c r i b e d i n t h i s paper i s f o r t u n a t e l y w e l l accep ted by many. and i t i s used b y some Japanese c a r m a n u f a c t u r e r s as a common methodology. [25,26,27,28.29,301 On t h e o t h e r hand, a number o f a t t e m p t s have been made f o r Dress f o r m i n g s i m u l a t i o n s u s i n g FEM f o r c a r body pane ls , and some i n t e r e s t i n g r e p o r t s have been pub1 i shed. [31,32,33,34,35,36,37,381 From t h e p r a c t i c a l p o i n t o f v iew, however, i t c o u l d n o t be s a i d t h a t t h e e f f o r t s t o s i m u l a t e f o r m i n g Processes o f t h e e n t i r e oanel w i t h a complex geometry have b r o u g h t abou t s u f f i c i e n t outcomes. A t tempts have been a l s o made t o d i v i d e f o r m i n g phenomena i n t o l o c a l i n d i v i d u a l phenomena by means o f numer i ca l models, and t o ana lyze them u s i n g FEM.[39,401

Accu ra te e v a l u a t i o n s o f f o r m i n g s e v e r i t i e s o f more complex shapes may be expec ted i n near f u t u r e by expanding such e f f o r t s and comb in ing them w i th t h e method d e s c r i b e d i n t h i s paper . The re fo re , t h e f o r m i n g s e v e r i t y e v a l u a t i o n method d e s c r i b e d i n t h i s paper s h o u l d be f u r t h e r deve loped u n t i l t h e complex and t r u l y 3-D shee t me ta l f o r m i n g s i m u l a t i o n u s i n g FEM reaches t h e p r a c t i c a l a p p l i c a t i o n s tage. A l though t h e a n a l y s i s O f P lane s t r a i n f i e l d s wh ich appear i n s t r a i g h t p r o f i l e has been a l l owed , t h e development o f a method f o r t h e e v a l u a t i o n o f c o r n e r s where complex d raw ing b e h a v i o r appears w i l l be necessary. The s l i p - l i n e f i e l d method appears t o be a p r o m i s i n g e f f e c t i v e method.[41,421 F i g . 2 0 shows an example i n which a wheel house i n n e r oanel i s s u b j e c t e d t o t h e d e t e r m i n a t i o n o f s l i p - l i n e f i e l d , and t h e P r i n c i p a l s t r e s s t r a j e c t o r i e s a r e de te rm ined .

The accumu la t i on o f compara t i ve d a t a is i m p o r t a n t t o i n c r e a s e t h e accu racy of Judgment i n t h e f o r m i n g s e v e r i t y e v a l u a t i o n approach wh ich i s n o t a method t o a n a l y z e t h e p r e s s f o r m i n g p rocesses d i r e c t l y .

Body data base

engineering 1 data

Stamping die Die drawing

Welding tool 8 equipment

F ig .19 I n t e g r a t e d CAD/CAM/CAE System

576

Moreover, t h e p r e c i s e a n a l y s i s o f a p p r o p r i a t e c l e a r a n c e between male and fema le d i e s i s a l s o i m p o r t a n t , by t a k i n g accoun t o f d e f l e C t l D n S o f d i e s and Press machines caused by p r e s s f o r m i n g l o a d s . Such d a t a s h o u l d be r e f i n e d i n t o knowledge base i n f u t u r e t o upgrade them system.

F u r t h e r r e s e a r c h and development on s i m u l a t i n g shee t m e t a l f o r m l n g and h i g h l y i n t e l l i g e n t CAE a r e expec ted t o promote t h e changeover f r o m " a r t " t o " s c i e n c e " .

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( a ) S l i p - l i n e ( b ) P r i n c i p a l S t r e s s F i e l d T r a j e c t o r i e s

F19 .20 A p p l i c a t i o n o f S l i p - l i n e Method t o Wheel House I n n e r Panel

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577