Component Batch Manufacture by Group Technology

8/3/2019 Component Batch Manufacture by Group Technology

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A u s t ra l i an Co n fe ren ce o nManufacturing Engineering17-19 August 1977

Component Batch Manufacture by GroupTechnology, a New Production System

A. W . BOUNDYLecturer. Darling Downs Institu te of Advanced Education, Toow oomba

SUMMAFLY Group Tech no lo gy i s p resen t ed a s a sy s t em wh ich p ro v id es t h e compo nent b a t ch man u fac tu r in g i n d u s t r yw i th t :he means o f c o n t ro l l i n g p ro d u c t i o n b y t h e u se o f , a sh o r t , s eq u en ced, p re -p l ann ed p ro d u c t i o n cy c l ecouple!d wi th a re- orga niza t ion of shop f l oo r machines and proc ess es .Ben e f t t s en u mera ted i n t h i s p ap er a re t h o s e w hich ma in ly acc ru e i n t h e a r ea s of p ro d u c t i o n p l an n in g an dc o n t r o l ; a c om pl et e e n u n c i a t i o n o f ' b e n e f i t s h a s b ee n p r e s e n t e d i n a n e a r l i e r p a pe r , Boundy ( 19 77 ).

A method commonly used f o r t he implement ation of Group Technology i s d e s c r i b e d i n s ome d e t a i l , a n d i t si n t e r a c t i o n w i t h t h e a dv an ce d t e ch n i qu e o f n u m e r i c al c o n t r o l i s d e a l t w i t h .Fi na l l y , a br i ef case s tu dy of a proposed Group Technology system fo r a medium siz ed manufact uring f i rm i so u t l i n e d .1 INTRODUCTIONManufacturing methods used t o produce bat che s ofcomponents and one off jobs has predominat ly favour-ed sy s tems d es ig n ed a ro un d t h e fu n c t i o n a l l ay o u t o fmachine t o o l s an d p ro cesses . The seg reg a t e d p l ace -men t o f machine t o o l t y p es i n t h e F u n c t i o n a l sy s t emne ce ss i t a t es numerous movements o f component ba tc hesi n o rc le r t o c o mp l et e t h e o v e r a l l o p e r a t i o n s e q ue n ce .A d e s i r e t o a c h i ev e c o n t r o l o v e r p r o d u c t io n t h ro ug h-p ut 't i. me s a s w e l l a s a t t a i n a smooth a n d e f f i c i e n tma te r i a l f l o w sys t em h av e b een fa c t o r s wh ich h av ef r u s t r a t e d f i r m s s i n c e m a nu f ac t ur i ng f i r s t be ga n.A measu re o f t h e su ccess o r o th e rw i se o f a f i rm ' smanufact uring sys tem can be gauged by a walk aroundl o o k a t t h e v ol um e of w ork i n p r o g r e s s l y i n g i d l eb etween o p e r a t i o n s an d a c lo se r i n sp ec t i o n o f t h eaccompany in g b a t ch p r o g ress d a t a w i l l u n d ou b ted lyrevea l. t h a t sh op f l o o r t imes a re measured b y mo nthsi n many case s . A s i t u a t i o n l i k e t h i s , w h e n w e e k scan laps e between su cces s ive op er a t i ons , makes pro-d u c t i o n c o n t r o l n o n - e xi s t e n t a n d d e l i v e r y d a t e s ama t te r of when they occur .D u rin g t h i s cen tu ry , o th e r t ech n o lo g i ca l imp ro ve -ments have , coupled wi th t h e advances achieved byn u mer i ca l l y co n t r o l l ed an d co mp uter a id ed machinet o o l s a n d p r oc e s s e s , b ee n a b l e t o b o o s t p r od u c ti o nf ig u r es many t imes o v e r . These b e n e f i t s , b ecau se o ft h e i r u n i v e r s a l a p p l i c a t i o n ha ve n o t g i v e n an y o nen a t i o n a s i g n i f i c a n t a dv a nt a ge f o r v e r y l o n g . Suc-c e s s i n m a n u fa c t ur i n g comes f r om a f i r m ' s a b i l i t yt o a c h ie v e b e t t e r p r o d u c t i v i t y f i g u r e s t h a n i t s com-p e t i t o r s . Low c o s t l a b o u r c o u n t r i e s s uc h a s J a p an ,Hong Kong, I nd ia , Taiwan and China enj oy an extre melyl ow ha n di c ap i n t h e p r o d u c t i v i t y s t a k e s .Aust ra l i -an technology must develop manufacturingsysteros which a r e more compat ib le wi th our fr eeth in k in g an d i n d ep en d en t way o f l i f e . These ch a rac t -e r i s t i c s h ave r e a c t e d in c r e a s i n g l y a g a i n s t t h e ma st er -s e r v a n t r e l a t i o n s h i p o f t h e p r e s e n t t r a d i t i o n a lsyst em. Semi-autonomous group working i s a systemwhich proposes a degree of independence and respon-s i b i l i t y f o r d a i l y t a sk s , b u t i t s u se i n A u s t r a l i at o d a t e h a s be en m a in ly r e s t r i c t e d t o wo rk er p a r t i c -i p a t i o n i n management. Such ap p l i c a t i o n s b ase t h e i r

imp ro ved p ro d u c t i v i t y f i g u r e s on t h e p ro v i s io n o f amore ch a l l en g in g , sa t i s f y i n g wo rkin g en v iro n men t fo remplo yees. O v e rseas , t h e se c t o r o f man u fac tu r in gi n d u s t r y w h ic h h a s . b e n e f i t t e d g r e a t l y , b o t h f ro m as o c i o l o g i c a l a n d t e ch n o l o g i c a l v i e w p o i nt i s compon-e n t ba t ch product ion when manufactured by a GroupTechnology system.2 THE CONCEPT OF GROW TECHNOLOGY2 . 1 D e f i n i t i o n'Group Technology i s a system of manufacture i nwhich a firm's component mix i s d i v id e d i n t o anumber of f am il ie s based on geo me tri cal shape whic 'hi s i n d i c a t i v e o f c e r t a i n t y p e s o f ma c hi n in g o p e r a t -ion s . The machine too l and proc ess assemblage i ss u b se q u en t l y a r r a n ge d i n t o g ro u ps o r c e l l s d e s ig n e dt o ma n uf a ct u re t h e a bo ve f a m i l i e s , s o t h a t e a chf a m i l y i s co mp le t e ly p ro cessed w i th in t h e co n f in eso f a p a r t i c u l a r c e l l i n a co n ti n uo u s o p e r a t i o nsequence . '2 . 2 Pro d u c t io n Co n t ro lThe mo st s i g n i f i ca n t d i f f e re n ce b e tw een t h e G roupTechnology and Funct ional sys tems i s t h e d eg ree o fco n t ro l o v e r p ro d u c t i o n w h ich i s i n h e r e n t i n e ac h.A comparison of th e component flow system s coup ledw i t h a n a p p r e c i a t i o n o f t h e p r i n c i p l e s w hi ch g ov er nt h e i r o p e ra t i on w i l l u n de r li n e t h i s d i f f er e n c e.F i g u r e 1 shows the two type s of l ayou t wi th a typ-i c a l component ba tc h ro ut e superimposed on each.The s e qu en ce o f o p e r a t i o n s r e q u i r e d f o r t h e b a t c hi l l u s t r a t e d i s , l a t h e , m i l l , i n s p e c t , g r i n d , g e a rc u t , d r i l l a nd i n s pe c t . I n t h e f un c t i o n a l l a y ou tt h i s m eans v i s i t i n g a s e p a r a t e s e c t i o n f o r e a c h op er -a t i o n , a s t h e r o u t e i n d i c a t e s . The f or em an i n c ha r geo f e ac h s e c t i o n a l o t t i n g t h e ba t c h on a r r i v a l t o ap a r t i c u l a r m ac hi ne a s i t becomes av ai la b l e . Theo p e r a t i o n i s then c ar r i ed ou t on ind iv i dua l compon-e n t s , w hi ch a r e r e t u r n e d t o t h e b a t c h b i n a n d remov-e d f ro m t h e s e c t i o n on t o t h e n e x t w he re a . i m i l a rp r o c e s s i s re pea te d. Even though each batch may beaccompanied b y i n s t ru c t i o n s a s t o when i t i s due outo f a s e c t i o n a n d o n t o t h e n e x t , t h e s e c o m pl e ti o nd a t e s a r e o f t e n u n a t t a i n a b l e a n d i n many c a s e s p a s t


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GR I N D I N GI = = 0FUNCTIONAL COMPONENT BATCH ROUTE

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CEL LUL AR COMPONENT BATC H ROUTE

Figu re 1 Comparison Between Fu nc tio naland Cel lu l a r Layout s.

b e f o re t h e b a t c h ev en a r r i v e s a t t h e s e c t i o n i nques t ion . Hence due da te s on o rde r s lo se th e i rs ig n i f i ca nc e and progres s chas ing becomes neces saryt o r e - e s t a b l i s h p r i o r i t i e s . Many b a t c h e s e n r o u t et hr ou gh t h e s y st e m l a g f u r t h e r a nd f u r t h e r b e hi n da nd t h e s t a t e of a f f a i r s on t h e s ho p f l o o r d e t e o r-i a t e s t o t h e e x t e n t where a l l a v a i l a b l e s p ac e i ss tacked wi th ba tches o f work i n p rogres s .On t h e o t h e r h an d t h e c e l l u l a r s y st e m d o es n o t h av et h e i n h e r e n t l a y o u t d e f i c i e n c i e s e x p er i e n ce d w i t ht h e f u n c t i o n a l l a y o u t . Each c e l l u l a r g ro up h a sw i t h i n i t s smal l boundar ies the machines neces saryto manufacture t he family of components f o r whichi t h a s b ee n s p e c i f i c a l l y d e si g ne d . T he l a y o u t i ssuch th a t work flow i s predominat ly through keym ac hi ne s f o r f i r s t o p e r a t i o n s a nd f i n a l l y t hr ou ghs u p p o r t m ac hi ne s f o r a u x i l i a r y o p e r a t i o n s . T h i sar rangement a lone sh or te ns component ro ut es by af a c t o r o f many t i m es a nd i n a d d i t i o n e s t a b l i s h e ss o l e r e s p o n s i b i l i t y f o r m a nu f ac t ur e . A no th er i m -p o r t a n t f e a t u r e of c e l l u l a r m a nu f ac t ur e i s t h a t com-ponents undergo a cont inuo us operat io n sequence soth a t they a r e p re fe rab l y no t b in f ed be tween machinetype s . This phi losophy develops t o a much high erd eg re e of p e r f e c t i o n a s o p e r a t i v e s w i t hi n a c e l lg a i n e x p e r t i s e i n t h e l o a d i n g a nd s eq u en c in g a s p e c t so f t h e i r c y c l i c p l an n in g t a s k . A ls o, i n t r a c e l ls t o r a g e an d t r a n s p o r t f a c i l i t i e s s u ch a s c o nv ey or so r m o bi l e p a l l e t s a l l o w f o r i n b a l a n c e b et we en s uc -c e s s i v e o p e r a t i o n s .The cont inuous op era t io n sequence of proc ess in g com-p o n e nt s i n a b a t c h h a s t h r e e v e r y i m p o rt a n t f e a t u r e s

which a re most appea l ing t o todays p roduc t ione n g i n e e r . F i r s t l y , c o n t in u o u s o p e r a t i o n s p r o vi d et h e s h o r t e s t p o s s i b l e t h r o u g h pu t t i me s . Secondly,by min imiz ing in te r -o pera t ion s to ra ge , work i n pro-g r e s s i s ke pt t o an abso lute minimum. Thi rd ly ,o r d e r s r e l e a s e d o n t h e s ho p f l o o r d u r i n g a p a r t i c u l -a r p r o du c t io n c y c l e a r e g u a ra n t e ed o f d e l i v e r y b ythe end of the cyc le, th er ef or e, .components can bep lanned fo r manufac tu re much c lose r , t o th e i r assemb-l y da te , thus r educ ing the amount o f s tock s necess -ar y t o ensur e an uni nte r ru pte d assembly programme.The above f a c t o r s con t r ib u te a f a r g rea te r measureo f c o n t r o l t o p r od u c t io n e n g i n e e r i n g t h a n i s poss-ib le wi th in a Func t iona l sys tem.3 IMPLEMENTATION OF GROUP TECHNOLOGY3.1 Component Family Form atio nA s s t a t e d i n t h e above d e f i n i t i o n , t h e f i r s t t a skof a Group Technology implementation i s t o d iv id ethe component mix into geometr ical ly s imilar famil-i e s . T h i s a s p e c t o f t h e e x e r c i s e i s most importantas the f i na l g roup ing of machine too l s and p roces sesdepends on the fa mi li es which emerge from th e com-ponent mix. A method which i s r e a d i l y a v a i l a b l eand cons idered by many t o be the most e f f ec t i ve , i sth a t o f component c l as s i f i ca t i on and cod ing .3 .1 .1 C la s s i f i c a t i on and CodingThe approach t o component fami ly format ion by c la ss -i f i c a t i o n a nd co di ng , r e q u i r e s a t o t a l a p p r a i s a l ofa f i r m ' s d ra wi ng f i l e i n o r d e r t o a l l o c a t e a c odenumber t o e ve ry component. Two numerica l cl a ss if -i ca t io n sys tems i n widespread use a re :( i ) the Br isch sys tem, Gombinski (196 9) , which i sd e s i g n - o r i e n t a t e d i e. components ar e grouped in tof a m i l i e s b y t h e s i m i l a r i t y o f d e s ig n m a n if e s t i nt h e i r o v e r a l l s h ap e.( i i ) the Opi tz sys tem, Opi tz (1970) , which i s pro-d u c t i o n - o r i e n t a t e d i e. components a re grouped i n t of a m il i e s r e q u ir i n g c l o s e l y s i m i l a r o r i d e n t i c a lt echnolog ica l p roces ses .

'Nei ther of the se two sys tems were designed express-l y fo r Group Technology; the Br isch sys tem ha s t ob e e x t e n s i v e l y m o di fi e d f o r t h e p u rp o se w h i l s t t h eOpi tz system, be ing a p roduc t ion o r i en ta t ed sys tem,r e q u i r e s min or a l t e r a t i o n s t o s u i t t h e u ni qu e r e -quirements of the f i rm concerned. The Br isch sys temr e q u i r e s sp e c i a l i s e d c o n su l t at i o n f o r i t s i n s t a l l a t -ion and proves r a th er cos t ly . There i s l i t t l e doubtt h a t i f a f i rm i s p r e p ar e d t o make a s u b s t a n t i a li n ve s tm e nt i n a B r i sc h c l a s s i f i c a t i o n s ys te m , i twould .pave t he way to a s a t i s f ac to ry implementat ionof Group' Technology. Such su cc es sf ul examples a sF e r a n t i L t d . , Durie (196 9), and Serck Audco, Ranson(1972) , speak we l l fo r th e Br isch sys tem when pro-p e r l y a p p l i e d .The advantage of the O pi tz over th e Br isch code i st h a t it i s r e a d i l y a va i l ab l e a t no r e a l c o s t t o af i r m , a l t h ou g h m o d i f i c a ti o n s a r e n e c e s s a r y t o o neo r b o t h p a r t s o f t h e co de . Once t h i s i s d on e,coding can be c ar r i ed out by a f i r m' s own personnel .The Opitz code i s a two p a r t c o d e, t h e f i r s t p a r tp rov id ing a geomet r i ca l de scr ip t ion o f the componenta nd t h e s e co nd p a r t g i v e s , d i m e ns i o na l , m a t e r i a l ,and gene ral manufactur ing info rmat ion. The code ha si nd ep en de nt d i g i t a l s i g n i f i c a n c e , s o t h a t e x t r ad i g i t s may be added t o provide more informat ionv i t h o u t a f f e c t i n g p r e v io u s d i g i t s . F i gu r e 2 showsa m od i fi e d v e r s i o n o f t h e O p i t z c od e i n s t r u c t u r e


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GEOMETRICAL CODE

Figure 2 Modi f ied Opi t z c l a ss i f i c a t io n Sys tem.

SUPPLEMENTARY CODE

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form, which ha s been develo ped f o r a Group Technologyinvest igat ion, Boundy (1975) .

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Once a component has been cl as si f i ed i n t o one ofth e classes shown under the f i r s t d i g i t , t h e r emain-ing d i g i t s o f th e geomet r i ca l code a r e se l ec t ed f roma s e p a r a t e c h a r t ( on e f o r ea c h c l a s s ) , s p e c i a l l ys e t o u t t o i n d i c a t e t h e g e o m et r i c al s h ap e c h a r a c t e r -i s t i c s i n t e c h n o l o g i c a l o r d e r o f p r o d uc t i o n. F orexample , p l a in ro t a t i ona l component s have t he i re x t e r n a l s h ap e d e sc r i b ed f i r s t , f ol lo we d by i n t e r n a lshape, t hen p lane su r f ace f ea tu r es (keyways , f l a t s ,h ex ag on s e t c . ) a nd l a s t l y t h e t y p e an d p a t t e r n s o faux i l - i a ry ho les . Another p rov i s ion o f th e code i st h a t wi th in each d i g i t c l a ss shown in F igure 2, t heorder o f complex i ty o f f ea tu r es in c rea ses f rom no th -in g t:o a maximum f o r ca te go ry 9. Fi gur e 3 i l l u s t r a -t e s f e a t u r e s f o r t h e se co nd and t h i r d d i g i t s o f t h epla in ro ta t i on al family of components. By stu dyin gt h e f e a t u r e s of t h e s ec on d d i g i t ( e x t e r n a l s h ap ee l e m e n t s ) , o ne c an s e e t h a t t h e s e e l e m en t s a r e a l lproduced on a la th e. The f i r s t category (0) in-dicat :es no ex te rn al machining, whereas th e nextt h r e e (1, 2 and 3 ) des cr ib e elements which can bep r o d ~ ~ c e di thout t he need t o rever se the componentin the l a th e chuck . Ca tegor i es 4 , 5 and 6 i n w hi chthe component i s s t e p pe d t o b ot h e n d s r e q u i r e s r e -ve r sa l i n the l a th e o r a second set -up on ano thermachi.ne. Categories 7 , 8 and 9 a re complex op erat -i o n s r e q u i r i n g s p e c i a l s e t- u p s a n d / o r t h e a p p l i c a t -ion o f more sk i l l e d t echn iques . The th i r d d i g i t( i n t e r n a l s ha pe e l em e nt s ) i s s t r u c t u r e d s i m i l a r l yt o d i g i t 2 , b u t d e s c r i b es i n t e r n a l b o r i n g f e a t u r e s .

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3 . 1 . 2 The Computer Print-out

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P a r t o f t h e c od in g e x e r c i s e c o n s i s t s of e n t e r i n g a l lcomponent i nformat io n on t o coding da ta she et s whicha r e c a r e f u l l y d e s ig n ed t o t a k e a dv a nt a ge o f t h epr in t -ou t c ap ab i l i t y of the computer . Punched car dsar e produced, one fo r each component and a pr in t -ou tob ta ined in ascending numer ica l o rder o f the geometr -i c a l code. Components a r e au tomat i ca l ly so r t ed in tof a m i l i e s a c co r di n g t o t h e f i r s t d i g i t - t h e c l a s sd i g i t , F igure 2. F igure 4 shows a smal l sect ion ofa pr int - out on which can be seen the type of in -fo rmat ion r equ i r ed fo r machine g roup ing ana lys i s .I t re pr es en ts seven components, showing th e end ofc l a s s ( 0 ) a nd t h e b e gi n ni n g o f c l a s s ( l ) . r o t a t i o n a l

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F igure 3 Geometr ical Dig i ts 2 and 3 oft h e P l a i n R o t a t i o n a l C l a s s .

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component s. Machining da ta con s i s t s of th e t o t a lnumber and sequence of o per at ons , machines, oper-a t io n and se t -up t imes. Par t numbers , ba tch s i ze sa nd a n nu a l q u a n t i t i e s a r e i n c l ud e d a s w e l l .

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CODE NO BATCHES PART NO OP. 1 OP. 2 OP.3 OP.4 OP.5 OP.6QTY PA EXTD MC OP SU MC OP SU MC OP SU MC OP SU MC OP SU MC OP SU

06600 2526 20 1 20 837066 05 40 3 5 . 9 22 18 . 9 16 10 . 76 4 0 . 73 2 0 . 79 20 25 .06700 2526 2 1 2 81222200 36 6 5 . 9 6 10 . 9 15 20 .07302 3626 1 1 1 X5746100 35 3 5 . 9 24 15 . 9 12 10 . 93 30 15 .07400 2551 1 1 . 1 ~ 6 3 0 6 0 3 9 4 0 6 5 . 9 18 35 . 9 14 10 . 76 4 0 . 73 2 0 .10000 1531 1 1 1 81005902 40 6 5 . 9 3 5 . 9 3 0 .10001 1481 40 4 160 X3208600 40 5 5 . 6 12 25 .10001 2230 20 2 40 X3208820 40 2 5 . 9 10 20 .

Figu re 4 Se cti on of Component Pri nt -ou t.Once the computer print-out i s o b t a i n e d , t h e a n a l y-s is l ead ing t o the fo rmat ion of mach ine g roups canbegin. Such an al ys is i s la rg el y manual, and manyv a r i a t i o n s o f t h e p r i n t- o u t c an b e o b t a i n e d t os imp l i fy the t as k . For example, a s oper a t io n twoi s probab ly ca r r i ed ou t on a key machine (opera t ionone be ing e i t h e r saw-off (40) , o r oxycu t ) , a p r i n t -o u t may b e o b t a i n e d l i s t i n g a l l c o mp on en ts r e q u i r -ing a ce r t a i n second opera t ion machine and f romt h i s a l o a di n g a n a l y s i s o f t h a t m ac hi ne i s r e a d i l yava i l ab l e . I n F igure 4, t he second oper a t io n mach-i n e (No 9) i s a cap stan la th e and a s imple programmew i l l p r i n t o u t a l l components r e q u i r i n g t h i s m ac hi ne .T he e n s u i ng a n a l y s i s w i l l r ev ea l the number o f t hes emachines required.There a r e no doubt many sa t i s f ac to ry l ayo u t s whichc an b e pr o po s ed , b u t t h e s k i l l o f t h e a n a l y s t w i l lu l t im ate l y dec ide how c los e t o the optimum w i l l bet h e f i n a l l a y ou t .

normal ly used mid-cycle , some prel imin ary op era t io nsa r e u s u a l l y n e c e s s a ry t o p r o v id e l o c a t i n g o r r e -f e r en c e s u r f a c e s , w h i l s t f i n a l o p e r at i o n s i n vo l v in gp l a n e s u r f a c e s ( ke yw ay s, f l a t s e t c . ) may b e c a r r i e dout on suppor t machines. Such requirements arei d e a l f o r a c e l l u l a r s i t u a t i o n w it h t h e m ac hi ni ngc e n t r e f i l l i n g t h e r o l e o f k ey m ac hi ne a n d p ac e-maker.5 A PROPOSED GROUP TECHNOLOGY SYSTEMAny proposed Group Technology sys tem sh ou ld be de-s i g n e d ar ou nd t h e f o l l o w i ng f o u r p r i n c i p l e s :( i ) a group layo ut of machines.( i i ) a s h o r t , r i g i d , r o l l i n g pr od uc ti on c yc le .( i i i ) a p l a nn e d l o a d i n g s eq ue nc e.( iv ) a s in g le cyc l e f low con t ro l o f componen t

s t o c k o r d e r i n g .

4 NUMERICAL CONTROL AND GROUP TECHNOLOGYRaw M a t e r i a l s F in i s h e d P r o d u c t s

Most fa ct or ie s and workshops of any s i z e today, a reequ ipped wi th numer ica l ly c on t ro l l ed mach ine t oo l s .Because of th e out stan ding advances made i n desig nof N C m a ch in in g c e n t r e s a nd l a t h e s d u r i n g t h e l a s t CELLS PRODUCTt e n y e a rs , a b r i e f l oo k a t t h e c o m p a t i b i l i t y oft h e s e m a c hi ne s w i th a GT c e l l f o l lo w s .' PRODUCTNC l a t h e s a r e u s u a l l y f i r s t o p e r a t io n m ac hi ne s an du n l e s s s u c h m ac hi ne s a s k ey s e a t e r s , d r i l l s an dm i l l s a r e r e a d i l y a v a i l a b l e f o r a u x i l i a r y o p e r at -i o n s , NC l a t h e s g e n e r a t e a f a r g r e a t e r v olume o fwork i n p ro g r e s s t h a n e x i s t e d b e f o r e t h e i r u s e .F or t h i s r ea s o n a n NC l a t h e i s an i de al pacemakerf o r a GT t u r n i n g c e l l wh er e s u p p o rt m a ch in es a r eof su i t ab le type and number t o ensure a con t inuousflow of components .I t h a s be en s t a t e d , C ra ve n ( 19 73 ), t h a t i n c e l l u l a rm a nu f ac t ur e t h e d e s i r e t o r e d uc e b a t c h s i z e s i n -e v i t a b l y l e a d s t o a n i n c r e a s e i n s e t- up t i m e s,e s p e c i a l l y on c o n v e n t i o n a l l a t h e s w hi ch r e q u i r eto o l changes and numerous s top se t t in gs . Such ane f f e c t may be a v o id e d b y i n s t a l l i n g a n N C l a t h ewhich has an extreme ly low set -up t ime. This fe at -u re a l lo ws sma l l e r ba tches t o be manufac tu red ec -onomical ly wi thout inc rea sin g th e volume of worki n p r o g re s s .M ac hi nin g c e n t r e s ha ve t h e c a p a b i l i t y o f f u l f i l l i n gth e ro l e o f a number o f d i f f e r e n t t ypes o f conven-t i o n a l m a ch in es . They a r e p a r t i c u l a r l y u s e f u l f o rmachining a s in g le complex component, th e number ofo p e r at i o ns p o s s i bl e b e in g r e s t r i c t e d b y ' t h e l i m i t a t -i o n s o f s i z e o f t h e i r t o o l ma ga zi ne . I t i s claimed,Craven (1973) th a t t h i s inadequacy i s l e s s en e d i n aGT c e l l wh er e t o o l v a r i e t y f o r a c ho se n c omponentf ami ly i s l im i t e d , t hus widening the mach iningc e n t r e ' s p r o ce s s i n g c a p a b i l i t y t o i n c l u d e a s ub -fam ily of components. A s t he mach in ing cen t r e i s

MATER l A LSU PPLY

TRANSPO

,ASSEMBLYPRODUCTION ASSEMBLY-

C E L L S L l N ECELLSI

I COMPONENT STORES I*Vendor I tems

Figure 5 Proposed Group Technology Cell System5.1 A Case StudyF igure 5 i s a p ro po se d f u l l y i n t e g r a t e d p r od u c t io nsystem f o r a fa ct or y employing some 700 workersmanufac tu r ing equipment fo r the sugar ha rves t ingin dus t ry . The company has a la rg e conven t ionalmachine-shop toge ther wi th an ex te ns iv e f ab r i ca t io nse ct i on, because a la rg e number of components ar eoxy-cut and welded t o form sub-ass emblies . Vendori tem s ar e bought i n to supplement in-house compon-en t s i n sub-assembly and f i n a l a ssembly l i ne . Rawmate r i a l s tock s a r e h igh and vendor i t ems .acco un tf o r a s u b s t a n t i a l pe r ce n ta g e o f t h e f i n a l pr o du c t.The company developed from very sm all b egin ning sand ha s expanded t o i t s p r es e nt s i z e d r a m a t i c a l l yo v er t h e l a s t f i v e y e a r s d ue t o a n e v e r i n c r e a s i n ghome and expor t marke t. P roduc t ion f a c i l i t i e s based


5/5

on a f unc t i ona l l ayou t a r e p res en t in g the companywi th d e l i ve r y da te p roblems, excess ive work i n p ro -g re ss , a l a rg e vo lume of f in i sh ed s tock s and p ro -d u c ti o n p l a n ni n g an d c o n t r o l d i f f i c u l t i e s wh ic hseem insurmountable.Fo llowing a t t endance a t a seminar on the p r in c ip lesof Group Technology, the f i rm 's top engin eersrecommended th a t a f e as ib i l i t y s tudy shou ld beunder t aken t o as ses s whe ther o r no t the new sys temc o ul d be s u i t a b l y a p p l i e d t o t h e f i r m ' s r a ng e o fp roduc t s .A thr ee months study fol lowed, culm inat ing i n thepres en ta t ion o f a r epo r t which p roposed th a t GroupTechnology had much t o o f f e r th e f i rm and i t s em-p loyees . A c l o s e r l o ok a t F i g ur e 5 w i l l show thatt h e m a t e r i a l f lo w s ys te m i s h i g h l y i n t e g r a t e d ,from t h e raw m a t e r i a l s t a g e t hr o ug h t o f i n a l a s s -embly. A complete ce l l u l a r sys t em i s env i saged ,i n v ol v i ng f o u r d i f f e r e n t c e l l t y pe s i n a d d i t i o n t othe product assembly which i s not planned fo r groupa ss em bl y a t t h i s s t a g e .Commencing a t th e inp ut of raw ma te ri al s, i s aun ique c e l l whose con t r a c t i t i s , v i a i n f o r m a t i o nfrom p l .anning and co n t r o l , t o p r epare and de l iv e rraw mate r i a l s t o the f ab r i c a t i on .and p roduc t ionc e l l s p r i o r t o t h e s t a r t of t h e r e le v a n t p ro d uc ti o nc y c l e , a n d t o t r a n s p o r t f i n i s h e d b a t c h e s a nd su b-a s se m bl ie s t o t h e i r ne x t d e s t i n a t i o n .F a b r i c a t i o n c e l l s a r e p r i m a r i l y c o n ce r ne d w i t h t h eproduct ion of fa br ic at ed components fo r sub-assemblyc e l l s a.nd t h e f i n a l a ss em bl y l i n e , a s w e l l a s p ro -v i d i n g c u t p l a t e , b l a n k s e t c . f o r m ac hi ni ng i n t h ep r od u ct io n c e l l s . F a b r i c a t io n c e l l s a r e n o t in -s t a l l e d , wi th h igh c ap i t a l cos t mach ines and henceth e i r ou tpu t can be var i e d f rom t ime to t ime , t ha ti s , t h e y h av e a re a s o na b l y f l e x i b l e s t r u c t u r e .P roduc t ion ce l l s on the o t her hand, once des ignedand pos i t i one d, ar e s t ru ct ur ed much more r . ig id lyt o manufacture a ce r t a i n family of components ,h en ce t h e r e w ould b e n o d e s i r e t o a l t e r t h i s u n iq uecap aci ty . Perhaps the replacement of convent ionalwi th NC machines or some minor changes might becon templa ted t o improve e f f i c i enc y , bu t ce r t a i n l yno r a d i ca l change would occur . P roduc t ion ce l l sdesigned t o produce components of a ce r t a i n geo-met r i ca l shape w i l l con t inue to do so i n the fo r -seeab le fu t u re , even though th e f i rm ' s p roduc t s mayundergo numerous changes in design and con st r uct ion .P roduc t sub-assembly c e l l s con s i s t mainly o f sp ec ia lf i x t u r e s t o a i d i n a ss em bl y t o g e t h e r w i t h w e l d er s ,d r i l l s and numerous hand opera ted to o l s r equ i r edf o r t h i s t y p e o f w ork . T he se c e l l s a r e h i g h l y f l e x -ib le and change cons tan t l y as new model s a r e i n t r o -duced r equ i r in g d i f f e r en t sub-assembl i es .The s y s te m i s i n h e r e n t l y s e l f - c o n t r o l l i n g i n r e s p e c tt o p r o du c t io n . Each c e l l wo rks t o a s h o r t d e f i n e dproduct ion cyc le which i s planned in advance. Workc a r r i e d o u t i n e ac h c e l l i s complete , th e f ragment-a t i o n of o p e r a t i o n s no l o n g e r e x i s t s , a n d re s p on s i b-i l i t i e s a r e c l e a r l y de f in e d. Shop f l o o r p l a nn i n ga nd c o n t r o l f o r t h e t o t a l m an u fa c tu re o f i n d i v i d u a lc e l l p r o d u c t s i s c a r r i e d o u t by t h e o p e r a t i v e s o ft h e p a r ti c u l a r c e l l s .I t i s conf iden t ly expec ted with the implementa t ionof t h i s system, th at th e f i r m' s component through-put t imes w i l l be control led and shor tened andt h e i r p r e s e n t l y l a r g e s t o c k o f work i n p r og r e s s

w i l l be reduced by a s much a s 30%.6 CONCLUSIONSThe Group Technology system, because of i t s sh or tdef ined and sequenced p roduc t ion cyc l e , i nher en t lyp r o v i d e s a r i g i d c o n t r o l o v e r p r od u c ti o n .A c l a s s i f i c a t i o n s y st e m p r o v i d e s a n e f f e c t i v e me th odof forming component f am il ie s and ena ble s the desi gnd ep ar tm en t t o e s t a b l i s h a d e si gn r e t r i e v a l f a c i l i t ytog eth er wi th a bank of component s tan dar dis at i onda ta , Boundy (1975).Qua l i ty Con t ro l i s ef f e c t iv e l y accompl i shed wi th i ni n d i v i d ua l c e l l s a s s u c c e s si v e o p e r a t i ve s m o n it e rth e performance of the precedin g ope rat ive and wi thc o nt in u ou s o p e r a t io n s r e c t i f i c a t i o n i s enforcedalmost immediately.A Group Technology material f low system i s a s e r i e so f p r e -p lanned , r e pe t i t i v e and wel l o rdered rou teswhich e n a bl e a n e f f i c i e n t an d r e l i a b l e i n t e r n a lt r a nsp or t syst em t o be developed .A wel l des igned compute r p r in tou t can g rea t ly f ac -i l i t a t e t h e a n a l y s i s of component f a m i l i e s w it hrespe c t t o machine a l l oca t io ns and load ings .When used i n a ce l l u l a r s i tu a t io n , numer ica l ly con-t r o l l e d ma ch in e t o o l s , b e ca u se o f t h e i r e x t r e me l ylo w s e t t i n g t i m es o f f s e t t h e t en de nc y t o i n c r e a s es e t t i n g ti m es a s i s t he case wi th conven t iona lmachines, when s mal le r batc hes ar e proposed.A c e l l s y s t e m i s u ni qu e f o r a p a r t i c u l a r f i r m ,be ing des igned t o cap tu re a l l componen ts p r e sen t lymanufactured by t he machine assemblage whichc u r r e n t l y e x i s t s on t he . s ho p f l o o r .Group Technology i s a t o t a l l y i n t e g r a t e d s ys te mo f m an uf ac tu re , i n c o r p o ra t i n g a l l a c t i v i t i e s o nt h e s ho p f l o o r , f ro m r aw m a t e r i a l s i n p u t t o f i n a lassembly.

7 REFERENCESBOUNDY, A. W. (1977 ), Group Technology, an EmergingNew System f o r Batch Manufacture , I.E. Abst.Management Conf eren ce, Uni. of New ca stl e, May 1977.COMBINSKI, J . (1969) , The Br i sch Class i f i ca t ion andGroup Technology, Proceedings of I nt er na t i on alSeminar , Sept . 1969, Tur in , I t a l y .OPITZ, H. (1970), A Cla ss i f i c a t i on Sys tem t o Des-c r ib e Workp ieces , Pa r t s 1 and 2, Pergamon Pr es s,Oxford, 1970.DURIE, F . R . E . (1969), Group Technology as A ppliedin a n E l e c t r o n i c Fi rm , P r o ce e d in g s of I n t e r n a t i o n a lSeminar , Sept . 1969, Tur in , I ta ly .RANSON, G.M. (1972), Group Technology , Pub. byMcGraw-Hill, 1972.BOUNDY, A.W. (1 97 5) , An Approach t o Group Tech-nology by Cla ss i f ic at io n and Coding, M. P h i l .The sis , Uni. of Aston in Birmingham, 1975.CRAVEN, F.W. (1973), Th e Use of NC i n Group Tech-nology, Th ird Annual GT Conference, She ff i e ld ,I . Prod. E., Nov. 1973.

Component Batch Manufacture by Group Technology

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