Combinations of processes in manufacturing

2.1.4 Combinations of processes in manufacturing

Vario u s co m bin at io n s o f d ifferen t fo rm in g p ro cesses o r co m bin at io n s o f fo rm in g, cu t t in g an d jo in in g p ro cesses h ave been fo u n d t o be su c- cessfu l o ver m an y years. Stretch drawing and deep drawing, fo r exam p le, assu m e an im p o rt an t ro le in t h e sh eet m et al p ro cessin g in d u st ry cf. Sect . 4.2.1 . Du rin g st ret ch d rawin g, t h e blan k is p reven t ed fro m slid in g in t o t h e d ie u n d er t h e blan k h o ld er by m ean s o f a lo ckin g bead an d bead in g ro d s o r by ap p lyin g a su fficien t ly h igh blan k h o ld er fo rce Fig. 2.1.32 . As a resu lt , t h e blan k is su bject ed t o t en sile st ress d u rin g p en et rat io n o f t h e p u n ch . So t h e sh eet m et al t h ickn ess is red u ced . Deep d rawin g, in co n t rast , is a p ro cess o f fo rm in g u n d er co m bin ed t en sile an d co m p ressio n co n d it io n s in wh ich t h e sh eet is fo rm ed u n d er t an gen t ial co m p ressive st ress an d rad ial t en sile st ress wit h o u t an y in t en t io n t o alt er t h e t h ickn ess o f t h e sh eet m et al cf. Fig. 4.2.1 . Fo r exam p le wh en d rawin g co m p lex bo d y p an els fo r a p assen ger car, st ret ch d rawin g an d d eep d rawin g m ay be co n d u ct ed sim u lt an eo u sly. Th e t o o l co m p rises a p u n ch , d ie an d blan k h o ld er Fig. 2.1.32 . Th e blan k h o ld er is u sed d u rin g st ret ch d rawin g t o act as a brake o n t h e m et - al, an d d u rin g d eep d rawin g t o p reven t t h e fo rm at io n o f wrin kles. Mo d ern p ressin g t ech n iq u es t o d ay p erm it t h e d esired m o d ificat io n o f t h e blan k h o ld er fo rce d u rin g t h e d rawin g st ro ke. Th e blan k h o ld er fo rces can be ch an ged in d ep en d en t ly at vario u s lo cat io n s o f t h e blan k h o ld er d u rin g t h e d rawin g st ro ke. Th e blan k is in sert ed in t h e d ie an d clam p ed by t h e blan k h o ld er. Th e fo rm in g p ro cess begin s wit h p en et ra- 22 Basic principles of metal forming draw ing w ith blank holder stretch forming deep draw ing + = punch blank holder blank die F Bl F Bl F Bl F Bl F St F St s s s s s 1 Fig. 2.1.32 Overlapping deep draw ing and stretch forming in the sheet metal forming process Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 t io n o f t h e p u n ch t o p erfo rm a st ret ch d rawin g p ro cess in wh ich t h e wall t h ickn ess o f t h e st ret ch ed blan k is red u ced . Th e bo t t o m o f t h e d rawn p art is su bseq u en t ly fo rm ed . Th e d eep d rawin g p ro cess begin s o n ce t h e req u ired blan k h o ld in g fo rce h as been red u ced t o t h e ext en t t h at t h e blan k m at erial is able t o flo w wit h o u t gen erat in g wrin kles o ver t h e ro u n d ed sect io n s o f t h e d ie. At t h e en d o f t h e d rawin g p ro cess, t h e blan k h o ld er fo rce is freq u en t ly in creased again in o rd er t o o bt ain a rep ro d u cible fin al geo m et ry by resp ect in g t h e st ret ch in g p o rt io n o f t h e d rawin g st ro ke. In ad d it io n t o d eep d rawin g, bo d y p an els are ad d it io n ally p ro cessed in t h e st am p in g p lan t by fo rm in g u n d er ben d in g, co m p ressive an d sh earin g co n d it io n s. A ch aract erist ic o f t h e bending p ro cess is t h at a cam ber is fo rced o n t h e wo rkp iece in vo lvin g an gu lar ch an ges an d swiv- el m o t io n s bu t wit h o u t an y ch an ge in t h e sh eet t h ickn ess. Th e sp rin g- back o f t h e m at erial resu lt in g fro m it s elast ic p ro p ert ies is co m p en sat ed for by overben d in g cf. Sect. 4.8.1 . An oth er p ossibility for obtain in g d im en sion ally p recise workp ieces is to com bin e com p ressive stresses with in tegrated restrikin g of th e workp iece in th e area of th e bottom d ead cen ter of th e slid e m ovem en t. Form ing is alm o st always co m bin ed wit h cutting. Th e blan k fo r a sh eet m et al p art is cu t o u t o f co il st o ck p rio r t o fo rm in g. Th e fo rm in g p ro cess is fo llo wed by t rim m in g, p iercin g o r cu t -o u t o f p art s cf. Sect . 4.1.1 . If n eit h er t h e cu t t in g n o r t h e fo rm in g p ro cess d o m in at es t h e p ro - cessin g o f a sh eet m et al p art , t h is co m bin at io n o f m et h o d s is kn o wn as blanking. W h ere great er p iece n u m bers are p ro d u ced , fo r m o st sm all an d m ed iu m -sized p u n ch ed p art s a p ro gressive t o o l is u sed , fo r exam p le in t h e case o f fin e-ed ge blan kin g cf. Sect . 4.7.3 . Ho wever, so lid fo rm - in g p ro cesses o ft en also co m bin e a n u m ber o f d ifferen t t ech n iq u es in a sin gle set o f d ies cf. Sect . 6.1 . Th e call fo r great er co st red u ct io n s d u rin g p art m an u fact u re h as bro u gh t abo u t t h e in t egrat io n o f ad d it io n al p ro d u ct io n t ech n iq u es in t h e fo rm in g p ro cess. St ackin g an d assem bly o f p u n ch ed p art s, fo r exam - p le, co m bin es n o t o n ly t h e classical blan kin g an d fo rm in g p ro cesses bu t also jo in in g fo r t h e m an u fact u re o f fin ish ed st at o r an d ro t o r assem - blies fo r t h e elect ric m o t o r in d u st ry Fig. 2.1.33 , cf. Fig. 4.6.22 an d 4.6.23 . Sh eet m et al p art s can also be jo in ed by m ean s o f fo rm in g, by t h e so -called h em m in g o r flan gin g Fig. 2.1.34 . 23 M ethods of forming and cutting technology Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Dividing, coating and m odifying m aterial property technologies will su b- st an t ially exp an d t h e field o f ap p licat io n co vered by fo rm in g t ech n o lo - gy in t h e fu t u re. Th is will allo w fin ish p ro cessin g in o n ly a sm all n u m - ber o f st at io n s, wh ere p o ssible in a sin gle lin e, an d will red u ce co st s fo r h an d lin g an d lo gist ics t h ro u gh o u t t h e p ro d u ct io n seq u en ce. 24 Basic principles of metal forming Fig. 2.1.33 Joining by parting Fig. 2.1.34 Joining by forming: hemming Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 2 Basic principles of metal forming 2.2 Basic terms 2.2.1 Flow condition and flow curve