Effect of Molding Parameters on Compression Molded Sheet Molding Compounds Parts

7/27/2019 Effect of Molding Parameters on Compression Molded Sheet Molding Compounds Parts

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E L S E V I E R Journal of M a|erials Processing Technology 67 (1997~ 105 I1[

J~arnalofProcessingT e c h n o l o g y

Effect of molding parameters on compression molded sheetmolding compounds partsK i - T a e k K i m ", J i n - H o J e o n g h Y o n g - T a e k h n h .,

" Sam.~ung Adtam 'ed lns i i :u te . / Technoh~gy, Suwon, S mtth Koreah Depar tme nt o[ Me, 'hanical Engineer ing, Korea A dtm we d Ins t i tu te ~1 Science and Technoh~gy, T at jon , South Korea

AbstractA d e t a i l e d e x p e r i m e n t a l s t u d y w a s c a r r i e d o u t t o d e t e r m i n e t h e e f f e c t s o f m o l d i n g v a r i a b l e s o n t h e p h y s i c a l a n d m e c h a n i c a lp ro p er ti e~ , o f c o m p r e s s i o n m o l d e d S M C ( s h e et m o l d i n g c o m p o u n d s ) p a r ts . S i m p l e c o m p r e s s i o n t e s ts u s i n g g r e a se o i l a n d m y l a r

s h e e t a s a l u b r i c a n t a t v a r i o u s t e m p e r a t u r e s w e r e e x a m i n e d i n c h a r a c t e r i z i n g t h e c o m p l e x e f f e c t o f S M C r e s in , f i b er g l as s , a n dt e m p e r a t u r e o n t h e f l o w s tr e ss o f S M C . T o i n v e s ti g a te t h e e f fe c t o f t h e m o l d i n g p a r a m e t e r s o n t h e t e n si l e a n d f l e x u r al p ro p e r t ie so f m o l d e d f l a t p a r t s , t w o d i f f e re n t m o l d t e m p e r a t u r e s a n d m o l d c l o s i n g sp e e d s w er e u s e d f o r f a b r i c a t i o n o f t es t s p e c i m e n s u n d e rp l a n e - s t r a i n c o n d i t i o n s . S u r f a c e r o u g h n e s s , t e n s il e a n d t h r e e - p o i n t b e n d i n g t e s t s w e re u s e d i n d e t e r m i n i n g t h e s u r f a c e q u a l i t ie s a n dt h e m e c h a n i c a l p r o p e r t i e s o f th e c o m p r e s s i o n m o l d e d S M C p a r t s . T h e f i b e r o r i e n t a t i o n a n d d i s t r i b u t io n i n t h e m o l d e d p a r t s w e r ea l s o i n v e s ti g a t e d b y t a k i n g p h o t o g r a p h s o f b u r n t f i at s p e c im e n s a n d p h o t o g r a p h s u s i n g S E M ( s c a n n i n g e l e c tr o n m i c r o s co p e } o fspec im ens o f T -shap ed c ross - sec t ion . ,~ 1997 E lsev ie r Sc ience S .A .Keywords: M olding parameters; Compression molded sheet molding compou nd

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

The appl ica t ions of polymers and composi te mate r i -a ls in automobi le and a i rc ra f t indust r ies a re inc reas ingbecause of the h igh s t rength- to-weight of the mate r ia l .SMC is a the rm ose t t ing mate r ia l tha t consis ts of unsa t -ura ted polyes te r res in and other addi t ives re inforcedwith randomly-dis t r ibuted chopped f ibe rglass sh 'ands .I t has evolved in to a pre fe r red candida te for automo-bi le body pane ls and o ther func t iona l compo nents s inceit offers a ttractive features, such as i ts lower mater ialcos t , tempera ture res is tance , and d imen siona l s tabi l i ty .One o f t he m a jo r m a nuf a c tu r ing t e c hno log ie s e m -ployed in fabr ica t ing SMC par ts i s compress ion mold-ing, which consis ts of fou r s teps: mate r ia l p repara t ion ,mold f i ll ing , cur ing , and e jec tion and cool ing . Thus , thef ina l mechan ica l proper t ies and sur face qua l i tie s of thecompress ion molded par ts a re dependent on the rheo-logica l charac te r is t ic s and molding condi t ions dur ingmold f i l l ing and cur ing.

*Correspond ing author . Fax: +8 2 42 8693210" e-mail :[email protected].

0924-0136/97/$17.00 1997 Elsevier Science S.A. A ll rights reserved.P I I S 0 9 2 4 - 0 ! 3 6 ( 9 6 ) 0 2 8 2 7 - 0

The mechanica l proper t ies and sur face qua l i t ie s ofSMC molded par ts wi th va r ious formula t ions a re oneof the major considera t ions when compar ing var iousSMC resins, improving existing resins or developi,~gnew formula t ions for the appl ica t ion of SMC in theautomobi le indust ry . In order to eva lua te the mechani-ca l proper t ies of the molded par ts , typica l ly one- footsquare p laques a re fabr ica ted us ing the g iven formula -t ions , then sample spec imens a re cut and tes ted fortens i le s t rength and modulus , f lexura l s t rength andmod ulus , and Izod or notched lzod va lues. The inspec-t ion of the sur face waviness i s ve ry impor tant in auto-mot ive manufac tur ing , s ince even smal l de fec ts shouldbe inspec ted in oute r pane ls such as hoods , t runks ,roofs, and fenders, to produce excellent surface f inish.Whi ls t the incorpora t ion of chopped shor t f ibe rglasss t rands in to the the rmose t t ing SMC res in has a l lowedtoughness and s t if fness to the cured molded par ts , thereis the need for a be t te r unders tanding of the overa l le f fec ts of SMC res in components , mold des ign andprocessing variables on the f low character ist ics andmechanica l pe r formance of the molded par ts . Thus ,Overley et a l . [1] has conducted work on the physicaltes t ing technique capabi l i t ie s and l imi ta t ions of m olded


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10 6 K.T. Kim et a l . /Journal t~]"Materials Processhlg Technoh~gy 67 (1997) 1 05-111

( U n i t : m m )A v e r a g e 1 2 7. r o u g h n e ss P r O f i le ~ , , l . - ' ~

Center Profile ~ N J - ' -- - - -*- - --~ ~-,-~- ~ ' U g h u ~e :f ~ 'w i 4 8 4 8

F i g . 1 . Sc h e m a t i c d i a g r a m o f su r f a c e r o u g h n e ss m e a su r e m e n t a n d n i n e m e a su r i n g p o i n t s .SMC par t s . They t r ied to de termine the sources andmagni tude o f the var iance invo lved in the phys ica l -proper t ies test ing of SMC resins. Farouk et al . [2] andM cEw en et al . [3] also i l~est igated the ef fects of cu r ingt ime, mold tempera tu re , and mold p ressure on them ech an i ca l p r o p e rt i e s o f t h e m o l d ed P M R - 1 5 / C 3 K an dSM C p a r t s .

In o rder to de termine the su r f ace qual i ty o f moldedpar t s , Hupp [4 ] developed a method to quan t i ta t ive lyevaluate the su r f ace waviness and ensured agreement o fthe quan t i ta t ive metho d wi th qual i ta t ive v i sual metho dsavailable. Vax ma n et al . [5] invest igate d the ef fect of theleng th o f the chopped f iberg lass on the rheo log ica lcharac ter i s t ics o f the SMC res in and the f iber o r ien ta-t ion . The p red ic t ion o f the f iberg lass o r ien ta t ion wasinvest igated by Advani et al . [6] .The ob jec t ive o f th i s work was to de termine therheo log ica l p roper ty o f an SMC charge used in exper i -ments and the ef f ec t s o f mold ing parameter s such as

mold tempera tu res o f 130 and 150C, mold c los ingspeeds o f 15 and 45 mm m in - t , and d i f f eren t wal lth icknesses o f 3 and 7 mm under p lane- s t r a in cond i -t ions , on Young ' s modulus , the f lexura l modulus , thetensi le s trength, and the surface roughness. Simple com-press ion tes t s us ing g rease o i l and mylar sheet as alubr ic ant at 28, 45, 60, and 75C w ere carr ied out inorder to charac ter ize the com bined ef f ec t o f the SM Cresin, the f iberglass , and the temperature on the f lowres i s tance o f SMC. In o rder to ob ta in the tens i le andf lexura l p roper t iez , f ive dog-bone type specimens sug-ges ted by ASTM [7] were made and used in the exper i -ments . The resultant f ive test results were averaged todetermine measures o f the tens ile and f lexura l s t reng ths .In add i t ion , a m echan ica l ly -m easur ing s ty lus -type su r-f ace- roughness tes ter was used fo r measurement o fsur f ace waviness , and a SEM was used in de termin ingthe ef f ec t o f mold geomet ry wi th a r ib ( cross - sec t ionalT- shape) on the f iberg lass d i s t r ibu t ion and o r ien ta t ionin the molded par t s under p lane- s t r a in cond i t ions .

2. ExperimentalThe SMC charge used in the p resen t inves t iga t ionw as p r o vi d ed b y A e k y u n g C h em i ca l C o . T h e l en gt h o f

the chopped f iberg lass used in the SMC formula t ionwas 25 .4 mm and i t s weigh t r a t io was 28%. The o thercomponen ts ar e l i s ted by par t s by wt% as fol lows:bisphenol type resin 25; low prof i le addit ive 75: TBPB

0 . 5

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0 . 0 ,0 . 0 0 . 2 0 . 4 0 , 6 0 . 8 1 . 0 . 2

STRA I N( b )

Fi g . 2 . Cu r v e s o f s t r e s s v s . s t r a i n o b t a i n e d f r o m s i m p l e c o m p r e s s i o nt e s t s u s i n g g r e a se o i l o n m y l a r sh e e t a s a l u b r i c a n t a t v a r i o u s s t r a i nr a t e s a t : ( a ) 4 5 C; a n d ( b ) 7 5 C .


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K.T. Kim 't a l . dm wm d o l , 'l lawr ia l~ Process ing Tec lmo loKv 67 997) 105 111 107

( t -bu ty l p e rb enz oa te ) 1" f i ll e r 140 : re l ea s e agen t {Z n-S t ) 4 : t h i c k e n i n g a g e n t ( M g O ) l " p i g m e n t 8 : a n ds t y re n e m o n o m e r : 3 .

I n o r d e r t o m a n u f a c t u r e t h e t e s t s p e c i m e n s , t h e i n -s t r u m e n t e d m o l d s e t - u p w a s m a d e a s d e s c r i b e d i nR e f . [ 8 ] . T h e c o m p r e s s i o n m o l d i n g w a s c a rr i e d o u tu s i n g a u n i v e r s a l t e s t i n g m a c h i n e b y S h i m a d z u C o .( m o d e l U H - 5 0 A , 5 0 t o n h y d r a u l i c ) . T h e f l a t a n d t h eT - s h a p e d c r o s s - s e c t i o n m o l d s e t s w e r e m a d e o f l o w -c a r b o n s t e e l . T h e d i m e n s i o n o f t h e f l a t p a r t w a s 7 6 . 7( w i d t h ) m m x 1 01 ( k n g t h ) r a m . T h e c r o s s - s e ct i o n a lr i b d i m e n s i o n w a s 9 .8 m m i n h e i g h t a n d 6 .3 5 m m i nw i d t h f o r t h e c r o s s - s e c t i o n a l T - s h a p e d m o l d . T h e i n i -t i al S M C c h a r g e t h i c k n e s s e s w e r e 1 1 a n d 7 m m t om a k e f i n a l p l a q u e t h i c k n e s s e s o f 7 a n d 3 r a m , r e s p ec -t i v e l y . T h e m o l d i n g t e m p e r a t u r e w a s c o n t r o l l e d b yf , -u r e l ec t r i c hea t ing rods o f 100 W capac i ty o f eachh n b e d d e d i n t h e t o p a n d b o t t o m m o l d s . T w o m o l d i n gtem pera tu re s , 130 and 150C , were us ed and mo ldc l o si n g s p e e d s w e r e e i t h e r 1 5 o r 4 5 m m m i n ~ , r e -s p e c t i v e l y . T h e m o l d i n g w a s c a r r i e d o u t u n d e r p l a n e -s t r a i n c o n d i t i o n s i n t h e l e n g t h d i r e c t i o n .

A m e c h a n i c a l l y - m e a s u r i n g s t y l u s - t y p e s m f a c e -r o u g h n e s s t e s t e r b y M i t u t o y o C o . ( S u f t e s t - 4 0 0 m o d e l )w a s u s e d i n d e t e r m i n i n g t h e s u r f a c e w a v i n e s s o f t h em o l d e d p a r t s . I n F i g . l , t h e s c h e m a t i c o f t h e s u r f a c ei n s p e c t i o n i s d e p i c t e d . S i n c e t h e m e a s u r e d d a t a i sg i v e n in l a i n a n d i s s c a t t er e d , d e p e n d i n g o n t h e m e a -s ur ing loca t ions , AA was de f ined in the p re s en t inves -t iga t ion a s fo l lows :

.| 'iA A - i = liiw h e r e y; r e p r e s e n t s t h e n m ~ a l d i s t a n c e f i 'o m t h e c en -t e r l i n e a s s h o w n i n F i g . l a n d n i s t h e m e a s u r i n gp o i n t n u m b e r s . N i n e p o i n t s i n t h e f l a t p l a q u e w e r es e l e c t e d f o r m e a s u r e m e n t .

T h e d o g - b o n e t y p e t e n s i o n a n d t h e t h r e e - p o i n tb e n d i n g s p e c i m e n s w e r e m a d e f r o m f iv e d i f f e r e n tp l a q u e s f o l l o w i n g t h e g u i d e l i n e s d e s c r i b e d i n t h eA S T M h a n d b o o k [ 7 ] . I n o r d e r t o d e te r m i n e w h e t h e rm e c h a n i c a l s ~ r e n g t h s a r e i s o t r o p i c i n t h e p l a q u e o rn o t , t h e t e s t s p e c i m e n s w e r e c u t f r o m t h e t w o d i r e c -t i o n s 0 a n d 9 0 t o t h e m a t e r i a l f l o w d i r e c t i o n u n d e rp l a n e - s t r a i n c o n d i t i o n s . A n I n s t r o n 4 2 0 6 w i t h m a x i -m u m e f f e c t i v e l o a d c a p a c i t y o f 1 5 0 k N w a s u s e d f o rthes e t e s t s . T he c ros s -head ve loc i ty us ed in expe r i -m e n t s w a s 0 . 5 m m r a i n - ~ f o r t h e t e n s i o n t e s t s . F o rt h e t h r e e - p o i n t b e n d i n g t e s t s , c r o s s - h e a d v e i o c i t i e s o f1 .2 a n d 2 .6 m m r a i n - ~ w e r e u s e d f o r t h e 3 a n d t h e 7m m p l a q u e t h i c k n e s s e s , r e s p e c t i v e l y .

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

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

T a b l e 1M e a s u r e d s n r f i ~ c e - r o u g h n e s s d a ~ a f o r ~ a r i , : u s m o l d i n g c o r ; J i t o n so b t a i n e d f r o m a f l a ~ p l a q u e w i l h a f in a l t h i c k n e s s o f 3 m mM o l d t e m p e r a t u r e ( C ~ 1 3 0 ! 5{ )M o l d c l o s i n g s p e e d i m m r a i n J / 1 5 4 5 1 5 4 5.4 .4 { txm~ 0 .40 0 .27 0 .42 ~ .295R . . .. . {~m~ 3,6S 2.11 3.53 ~9:~

t i o n s w e r e b u r n t t o p r o v i d e p h o t o g r a p h s f o r t h e i n -ves t iga t ion o f the f ibe r o r i en ta t ion and d i s t r ibu t ion . Inadd i t ion , a s cann ing e lec t ron mic ros cope by 3eo l Co .( m o d e l J S M 8 4 0 A ) w a s u s e d t o i n v e s t i g a t e t h e f i b e r -g l a s s d i s t r i b u t i o n s a n d o r i e n t a t i o n s i n a T - s h a p e dc r o s s - s e c t i o n s p e c i m e n w h i c h w a s m a d e u n d e r a m o l d -i n g t e m p e r a t u r e o f 1 50 C a n d a s p e e d o f 45 m mr a i n -

3 . Res u | t s and d i s cus s ionF ig . 2 (a ) and (b ) dep ic t the s t re s s and s t ra in cu rves

o b t a i n e d f r o m t h e s i m p l e c o m p r e s s i o n t e s t u s i n gg r e a s e o i l a n d m y l a r s h e e t a s a l u b r i c a n t a t 4 5 a n d75C . T he d imens ions o f the cy l indr ica l t e s t s pec imenu s e d i n t h e e x p e r i m e n t s w a s 3 2 . 4 m m d i a m e t e r a n d 9m m h e i g h t. F o u r l a y e r s o f t h e S M C c h a r g e w e r es t a c k e d t o m a k e t h e c y l i n d r i c a l s p e c i m e n . T h e s t a c k e din i t i a l s pec imen was s l igh t ly compres s ed to removepos s ib le vo ids be tween the l aye rs and to reduce s l ipd u r i n g c o m p r e s s i o n . T h e f i n a l h e i g h t o f t h e c y l i n d r i c a ls p e c i m e n a f t e r c o m p r e s s i o n w a s 2 r a m . D u r i n g t h ecom pres s ion s t ages , cons tan t s t ra in ra t e s o f 0 .005,0 . 001 , 0 . 05 , and 0 . 1 s -~ were ma in ta ined by con-t r o l l i n g t h e c o m p r e s s i o n s p e e d m a n u a l l y a c c o r d i n g t ot h e c o m p r e s s i o n l e v e l .

A p o w e r - l a w m o d e l w a s u s e d i n t h e p r e s e n t i n v e s t i -g a t i o n f o r r e p r e s e n t i n g t h e t h e o l o g i c a l c h a r a c t e r i s t i c so f t h e s t r e s s - s t r a i n d a t a o b t a i n e d f i ' o m t h e e x p e r i -me n t s a s fo l lows : # = C ( T ) g ''~ r~ ( M P a ) , w h e r e C a n dm a r e t e m p e r a t u r e d e p e n d e n t a n d s h o u l d b e d e t e r -m i n e d f r o m t h e e x p e r i m e n t a l d a t a . H e r e , T i s g i v e n i na b s o l u te t e m p e r a t u r e .

T h e v a l u e s o f m a n d C w e r e c a l c u l a t e d f o r f o u rd i f f e r e n t t e m p e r a t u r e s a n d d e t e r m i n e d a s a f u n c t i o no f t e m p e r a t u r e a s f o l l o w s : C ( T ) = 0.0091 exp{2100.3/T ) a n d r e ( T ) = 1 . 41 82 - 1 .5175 x 10- 9 exp( 5944. 4/ T ) .

I n T a b l e 1 , t h e a v e r a g e v a l u e s o f t h e m e a s u r e ds u r f a c e r o u g h n e s s , A A , a n d t h e m a x i m u m s u r f a c er o u g h n e s s v a l u e s , R m a x , a r e g iven . F rom th i s t ab le i tw a s f o u n d o u t t h a t a v e r a g e s u r f a c e - r o u g h n e s s v a l u e so b t a i n e d f r o m t h e p r e s e n t m o l d i n g c o n d i t i o n s w e r e i nt h e r a n g e o f 0 . 2 - 0 . 5 la m a n d d e c r e a s e d a s th e m o l dc l o s i n g s p e e d s i n c r e a s e d a t t h e s a m e m o l d t e m p e r a -tu re .


4/7

108 K . T . K in 1 e t a l . / 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 h J g y 6 7 ( ! 9 9 7 ) I 0 5 - ! ! i

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F i g . 3 . C o m p a r i s o n o f t h e e f fe c t o f d if f e r e n t m o l d i n g c o n d i t i o n s o n t h e t e n s il e p r o p e r t i e s w i t h f l a t - p l a q u e t h i c k n e s s e s o f : {a ) 3 m m ; a n d ( b ) 7 m m .

In add i t ion , the su r face was smooth er a t the cen ter thani t was a t the edges , due to the d i f f erence in the thermalh is to ry o f each r eg ion dur ing compress ion .

In Fig. 3(a) and (b) , the tensi le proper t ies for the f latp laques ob ta ined f rom two d i f f eren t p laque th icknessesof 3 and 7 mm wi th two d i f f eren t mold tempera tu res(130 and 1500C) and mold c los ing speeds (15 and 45mm min-~) are given, respectively. These f igures showthat the tens i le s t r eng ths were in the r ange o f 26-65M P a an d 4 4 - 6 5 M P a f o r th e 3 an d 7 m m t h ick n ess f la tplaques, respectively, whils t the elongation was in theranges o f 1 .5 -3 .9% and 3 .7 -4 .9%. Al though the ef f ec to f p laque th ickness , mold c los ing speed , and tempera-tu re on the mechan ica l s t r eng th was min imal , i t wasfound f rom the g iven data tha t the tens i le s t r eng thswere no t un i fo rm in the p lane d i r ec t ion o f the p laque:

the tensi le s trength in the 0 direct io n to the f lowdi rec t ion was la rger than the va lue in the 90 d i r ec t ion ,due main ly to the p lane- s t r a in cond i t ions dur ing com-press ion , where the chopped f iberg lass s t r ands seemedto a l ign in the f low d ir ec t ion . Thus , f low con t ro l dur ingco m p r es s io n m o l d i n g i s i m p o r t an t i n o b t a i n i n g i n - p l an eiso t rop ic mechan ica l p roper t ies .

In Fig. 4(a) and (b) , are presented the f lexural prop-er t ies ob ta ined f rom the th ree-po in t bend ing tes t s us ingthe compress ion molded p laques o f the two d i f f eren tth icknesses o f 3 and 7 mm under two d i f f eren t moldtempe ra tu res (130 and 150C) and m old c los ing speeds(15 and 45 mm min-~) . The f lexura l s t r eng ths were int h e ran g es o f 1 0 5 - 1 8 7 M Pa an d 9 4 - 1 5 8 M P a f o r t h e 3and the 7 mm th ickness p laques , r espect ive ly . S imi lar tothe results for the tensi le s trength, greater f lexural


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K.T . Kim et al . Jo urm d of Material ,~ Pr,'. 'e,~sing Tedmol,~g)' 67 1997) 1 0 5 I l I ~' )

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i 5 m m / m i n 4 5 r a m / r a i nt . _ _ I

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M o l d t e m p e r a t u r e s : 1 3 0 C(b)

1 5 m m / m i n 4 5 m m / m i nt I

1 5 0 C

- 3 0- . ~20 .~

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30- 20

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a

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Fig. 4. Com par ison of the effect of different mo lding con dition s on f lexural properties with f lat-plaque thicknesses of: ( a ) 3 m m ; a n d ( b } 7 m m .

s t r en g t h v a l u e s w e r e o b t a i n e d i n t h e 0 d i r e c ti o n c o m -p a r e d t o t h e 9 0 d i r e c t i o n t o t h e f l o w d i r e c t i o n , f o r t h es a m e r e a s o n s .

A p h o t o g r a p h o b t a i n e d f r o m t h e f l a t s p e c i m e n b u r n ti n a n e l e c t r o n i c f u r n a c e a t 5 3 0 C f o r 2 0 m i n i s g i v e n i nF i g . 5 . I n t h i s f i g u r e t h e f i b e r o r i e n t a t i o n a n d d i s t r i b u -t i o n i n t h e f l a t p l a q u e c a n b e o b s e r v e d .

I n F i g . 6 , a p h o t o g r a p h o b t a i n e d f r o m a S E M o f th eT - s h a p e d c r o s s - s e c t io n s p e c i m e n i s g i v e n . T h e s p e c i m e nw a s o b t a i n e d f r o m t h e c o m p r e s s i o n m o l d i n g o f a T -s h a p e d u n d e r a c r o s s - s e c t i o n m o l d t e m p e r a t u r e o f1 5 00 C a n d a m o l d c l o s i n g s p e ed o f 1 5 m m m i n - 'T h e s e f i g u r e s d e m o n s t r a t e c l e a r l y t h e d i s t r i b u t i o n a n do r i e n t a t i o n o f t h e f i b e r g l a s s s t r a n d s a n d t h e e f f e c t o f t h e

m o l d d e s i g n d u r i n g c o m p r e s s i o n m o l d i n g . T h e f i b e r -g l a s s s t r a n d s w e r e a l i g n e d i n th e d i r e c t i o n o f m a t e r i a lf l o w . I n a d d i t i o n , t h e r e e x i s t e d t w o d i f f e r e n t r e g i o n s ,o n e b e i n g t h e d e n s i f i e d S M C r e s i n r e g i o n a n d t h e o t h e rt h e d e n s i f i e d f i b e r g l a s s s t r a n d s r e g i o n . T h e f i r s t r e g i o nw a s f o r m e d i n t o a d e l t a z o n e a e a r t o t h e c e n t r a l r e g i o nb e l o w t h e t o p s u r f a c e , w h i l s t t h e s e c o n d r e g i o n w a sl o c a t e d n e a r t o t h e c o r n e r o f t h e r ib . I n s i d e t h e r i b , ac u r v e d d i s t r i b u t i o n o f t h e f i b e r g l a s s s t r a n d s w a s o b -s e r v e d . A t t h e f i a t f l a n g e r e g i o n , t h e o r i e n t a t i o n o f t h ef i b e r g la s s s t r a n d s w a s p a r a l l e l t o t h e t o p s u r f a c e o f th eg e o m e t r y . S i m i l a r o b s e r v a t i o n s w e r e m a d e f o r o t h e rs p e c i m e n s o b t a i n e d f o r d i f f e r e n t f l a n g e t h i c k n e s s a n dm o l d i n g c o n d i t i o n s . T h e f o r m a t i o n o f a d e n s i fi e d S M C


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11 0 K: T. Kim et a l. / Journal of Mater&Is Processing Technology 67 (1997) !05-111

(4) ....% ...... (2)

( 4 ) ( 2 )(1) Original fiber (3)distribution

Fig. 5 . Photo graphs of fiber dis t r ibut ion in a burnt f lat plaque of thickness of 7 mm (mold temp erature of 150C and mold clos ing speed of 15mm min - ').

..... I (2 ) (4)1'I ( 5 ) 1

(2 ) i i ! i i i i / !i l I i

i I( 3 )l l

( 4 )

(5 )Fig. 6 . SEM photographs at var ious locat ions in a T-shaped cross-sect ion specimen with a f lange thickness of 7 mm (mold temperature of 150Cand clos ing speed of 45 mm rain- ~) .

r es in r eg ion i s s t rong ly depende n t o n the su r face qual i tyof the molded par t s because o f the d i f f erence o f thermalcon t r ac t ion o f the SM C res in and the f iberg lass s tr ands .

4. ConclusionsIn the present invest igat ion, the f low resis tance wasmeasured and f i tt ed to a pow er - law model and theef f ec t s o f mold ing parameter s on the mechan ica l p rop-

er t ies o f the compress ion molded par t s were de ter -mined . Under the p resen t mold ing cond i t ions , i t wasf o u n d t h a t a s t h e m o l d t em p er a t u r e an d t h e s p eeddecreased , the tens i le modulus increased , a l though thef lexural modulus values were scat tered. The f iber glass

was d i s t r ibu ted r andomly in i t i a l ly , bu t a l igned to thef low d i r ec t ion fo r f ia t p la te mold ing . For T- shapedmold ing , a r es in -dens i f ied de l ta r eg ion near to the cen-ter , below the top f iat die, was formed, whils t a f iber-g lass -dens i f ied r eg ion fo rmed around the corner o f ther ib was in agreement wi th the f low d i r ec t ion o f theSMC res in .

AcknowledgementsT h e au t h o r s w i s h t o ack n o w l ed g e th e g r an t f r o m

K O SE F an d t h e M i n i s t r y o f C o m m er ce an d I n d u s t ryu n d e r w h i ch t h i s w o r k w as p o s s i b l e an d A ek y u n gC h em i ca l C o . f o r p r o v i d i n g SM C m a t e r i a l s .


7/7

K . 7". K im e l a l . ' Jo in 'hal o . f M ater ia Ls Pr ,' ces. s ing Te , 'h lmh,~ ,9 , 67 (19 97) 10 .5 111 1 iRe f e r en c e s

[1] J .R. Over ley , J . Cr ichton and R, Sx~ 'anson, SMC plDsical prop-e r ty t e s t in g -t e s t t ech n iq u e cap ab i l i t ie s an d l imi t a t io n s . 4 3 r d A n -min i C o~gl Pr oc . , T !u ' N ,~ . O /H ie P !mt i c .~ lmh~s l r v , i r a '. . 19 ,q '8 ,S , : s s ' i , n 13-D, pp. I 4.

[2] A. Farouk and T.H. K,aon. Effect of process ing parametcr .~ onc o m p r e s s i o n m o l d e d P M R - t 5 C 3 K c o m p o s i t e s . P , / tm . ( ', ,, rap . .I ! (61 11990) 3 7 9 - 3 8 6 .[ 3] D A . M c E w e n a n d J . N ew b o u ld , E f f ec~ o f mo ld in g co n d i t io n s o nt h e s u r f a c e c o m p o s i t i o n s o f s h e e t m o l d i n g c o m p o u n d , P , , / v m .G , m p . , 1 2 (5) (1991} 315--319.

[ 4 ] S . S . H u p p , A q u an t l t a . t i v e me th o d lo t an a ly s i s o f s u r f aces o fm o l d e d S M C p a r t s , 4 3 r d A m m a l C o n t l P r o < , T h e S ' oc . , ! t t h eP l a s t i c s l n & ~ s t r ) , h w . , 1 9 8 8. S e s s i o n 1 0 - . 4 , pp. I 4.

1 5 ] A . V ax man an d M . N ar k i s , S h o r t - f ib e r - r e in f o r ced th e r mo p las -t ics . Par t l l l : ef fect o f t iber length on rheo~ogicM proper t ies andl ib e r o r i en ta t io n , P o /y m. ( ' , r a p . , 1 0 16~ (1989~ 454 462.

[61 S .G. Ad~ ani and C .L. Tu cker , A numeric al s imula t ion of shor~.f iber or ientat ion in cu .npre. , , s im~ molding, P o l y m . C o m p . , 1 1 ! 3 1(~ )9111 D64 t73 .

[71 ,4:,,m,d B , , ,k , d A S F M S t ,, M a r d ~ , S tan d a r d l e s t me | h o d ~ o r~cnsde proper t ies of p las t ics (metr ic) , D638M-89. pp . ~6,q 173and S tandard tes t methods f~r f lexura ' , proper t ies of unrein-[breed and reinforced p las t ics and ,qo , : : r ical insulat ing mater ia ls(metric}, D 7 9 0 M - 8 6 , 1 9 8 9 , p p . 2 9 0 2 9 7 .

[ 8] J . H . J eo n g , K . T . K im an d Y . T . | m , P lan e - s t r a in co mp r es s io nmo ld in g an a ly s i s o f s h ee t mo ld in g co mp o u n d s in l t a t an d c r o s s -s ec t io n a l T - s lmp e mo ld s . J . M ater . Pr , , ces s . T~ 'chnol . . 57 ~]996)320- 331.

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