Active hydro-mechanical draw ing

Hyd ro -m ech an ical d eep d rawin g allo ws t o ach ieve a sign ifican t ly larger d raw rat io t h an t h at ach ievable in co n ven t io n al d rawin g o p era- t io n s. W h ilst t h e lim it in g d rawin g rat io u sin g co n ven t io n al t ech n o lo gy is b 2.0, d eep d rawin g ratio lim its of u p to 2.7 can be ach ieved in h yd ro -m ech an ical d eep d rawin g. Sin ce n o in t erm ed iat e d rawin g an d an n ealin g o p erat io n s are req u ired , very co st -effect ive fo rm in g is p o ssi- ble. Th e t o o l co st s can also be red u ced becau se o f t h e red u ct io n in t h e n u m ber o f n ecessary fo rm in g o p erat io n s. An o t h er n o t able ben efit is t h e q u alit y o f t h e su rfaces o f t h e d rawn p art s, as t h e sh eet m et al h as n o t been d rawn o ver a rigid d rawin g ed ge bu t o ver a flu id bead . Co st s fo r fin ish p ro cessin g o p erat io n s su ch as p o lish in g o r grin d in g are su bst an - t ially red u ced o r o ft en co m p let ely elim in at ed . Du e t o t h e p ressin g o f t h e blan k again st t h e p u n ch wh ich red u ces t h e am o u n t o f sp rin g back, d im en sio n ally accu rat e p art p ro d u ct io n is p o s- sible. Th is is p art icu larly im p o rt an t in reflect o r p ro d u ct io n , as n o t o n ly m easu rem en t t o leran ces bu t also o p t ical q u alit ies are t est ed . Th e t h ick- n ess of th e sh eet m etal for h yd ro-m ech an ically d eep d rawn p arts rem ain s con sisten t with in n arrow lim its. Th is ap p lies p articu larly to th e sm all red u ction in th ickn ess on th e base rad ii, so th at th in n er blan k can fre- q u en tly be u sed for form in g th e d esired p art. Press fo rce is h igh er in h yd ro -m ech an ical d rawin g t h an in o t h er fo rm in g m et h o d s u sin g rigid t o o ls, d u e t o t h e react io n p ressu re in t h e wat er co n t ain er. Here, t h e slid e fo rce F St [kN] is t h e su m o f t h e co n ven - t io n al fo rm in g fo rce F U [kN] an d t h e react io n fo rce F Re [kN], wh ich act s o n t h e p u n ch su rface t h ro u gh t h e p ressu re m ed iu m Fig. 4.2.11 . Dep en d in g u p o n t h e p art icu lar blan k m at erials bein g p ro cessed , t h e fo llo win g p ressu res o ccu r in t h e wat er co n t ain er: – alu m in iu m : 50 – 200 bar – st eel: 200 – 600 bar – st ain less st eel: 300 – 1,000 bar

4.2.5 Active hydro-mechanical draw ing

Dep en d in g o n t h eir d esign , large-p an el co m p o n en t s fo r t h e au t o m o bile in d u st ry su ch as h o o d s, ro o fs an d d o o rs p o ssess o n ly m in im al bu cklin g st ren gt h in t h e cen t er regio n o f t h e p art s. Th e reaso n fo r t h is is t h e lo w 188 Sheet metal forming and blanking Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 level o f act u al d efo rm at io n in t h is area. Th e sm all am o u n t o f d efo rm a- t io n m ean s t h at in su fficien t st rain h ard en in g t akes p lace an d t h e p an - els are liable t o give way u n d er o n ly a lo w ap p licat io n o f p ressu re, resu lt in g in lo w d en t resist an ce. Th is lo w co m p o n en t st abilit y h as a n egat ive effect o n crash resist an ce o f veh icles an d resist an ce t o im p act fro m h ailst o n es. In ad d it io n , u n d esirable vibrat io n s can o ccu r at cert ain d rivin g sp eed s. As a resu lt , h igh er st ren gt h m at erials o r rein fo rcin g elem en t s an d bead in gs are u sed . In so m e cases, t h is can co n sid erably raise t h e u n it co st o f t h e p art an d in crease t h e co m p o n en t weigh t . “Act ive h yd ro - m ech an ical d rawin g” Act ive Hyd ro -Mec is a d efo rm at io n p ro cess t h at allo ws t o o verco m e t h ese p ro blem s an d red u ce t h e t o o l co st s. Range of parts Th e Act ive Hyd ro -Mec m et h o d can be u sed t o p ro d u ce a wid e ran ge o f p art s, in clu d in g p ract ically all large p an els an d , p art icu larly, flat ext er- n al bo d y p art s o f a veh icle su ch as h o o d s, t ru n klid s, ro o fs, d o o rs an d fen d ers. Th e sm aller t h e d egree o f d efo rm at io n req u ired in t h e first o p erat io n wh en p ro d u cin g an o u t er p an el co n ven t io n ally: d eep d rawin g o f t h e 189 Deep draw ing and stretch draw ing Fig. 4.2.11 Force versus displacement during hydro-mechanical deep draw ing slide force F = F + F ST U Re reaction force F Re forming force F U draw ing path s force F Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 co n t o u red blan k, t h e m o re su it ed is t h e o p erat io n fo r u sin g t h e Act ive Hyd ro -Mec m et h o d . Operating principle Th e Act ive Hyd ro -Mec m et h o d in vo lves fo rm in g wit h an o p erat in g m ed iu m o il-wat er em u lsio n , in wh ich a large-size blan k is clam p ed all aro u n d wit h a wat ert igh t seal bet ween t h e fem ale d ie an d t h e blan k h o ld er – in t h e fo rm o f a wat er co n t ain er Fig. 4.2.122 . At t h is st age, a d efin ed , p art -sp ecific gap exist s bet ween t h e clam p ed blan k an d t h e p u n ch . As so o n as t h e blan kh o ld in g fo rce h as bu ilt u p , t h e em u lsio n is act ively in t ro d u ced in t o t h e wat er co n t ain er by m ean s o f a p ressu re in t en sifier an d a d efin ed p ressu re is bu ilt u p d ep en d in g o n t h e p art bet ween 20 an d 30 bar. Th is p ressu re cau ses a co n t ro lled bu lgin g o f t h e blan k wh ich is p re-st ret ch ed o ver wh at is t o beco m e t h e en t ire su rface o f t h e co m p o n en t u n t il it co m es t o rest again st t h e p u n ch in t h e cen t er o f t h e p u n ch su rface. Th is co n t ro lled exp an sio n o f t h e sh eet m et al resu lt s in wo rk h ard en in g o f t h e wo rkp iece wh ich lead s t o a su bst an t ial im p ro vem en t in bu cklin g st ren gt h o f t h e fo rm ed p art . Aft er t h e p re-st ret ch in g p ro cess, t h e wh o le syst em – blan k h o ld er, blan k an d fem ale d ie – is p ressed u p ward s again st t h e st at io n ary p u n ch . Th is p ro cess co rresp o n d s t o t h e co u n t er-d rawin g p rin cip le Fig. 4.2.4 in wh ich t h e em u lsio n is d isp laced . Du rin g t h e p ro cess, t h e p ressu re level can be kep t co n st an t o r can be regu lat ed t o in crease o r d ecrease p ro gressively o r d egressively. Aft er co m p let io n o f t h e d rawin g p ro cess, t h e em u lsio n p ressu re is act ively bu ilt u p t o a m axim u m o f 600 bar in o rd er t o en su re o p t im u m ap p licat io n an d fo rm at io n o f t h e blan k again st t h e co n t o u r o f t h e p u n ch . Press Th e p ress d evelo p ed fo r t h e Act ive Hyd ro -Mec-p ro cess is a d o u ble- act io n st raigh t -sid ed p ress d esign wit h Hyd ro -Mec p ressu re in t en sifier an d a q u ick d ie ch an gin g syst em . Figure 4.2.13 p ro vid es a sch em at ic view o f t h e p ress. Th e p ress fo rce o f m ax. 50,000 kN is ap p lied fro m belo w by eigh t cylin d ers lo cat ed in t h e p ress bed . Six blan k h o ld er cylin d ers in t h e p ress cro wn ap p ly a blan kh o ld in g p ressu re o f m ax. 16,000 kN d u rin g t h e p re-st ret ch in g p ro cess. Six p o wered m ech an ical st o p s can be ad ju st - ed fo r each in d ivid u al p art t o d et erm in e t h e lim it o f t h e d raw d ep t h . 190 Sheet metal forming and blanking Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th e Hyd ro -Mec eq u ip m en t co n sist s m ain ly o f a p ressu re in t en si- fier t ran sm issio n rat io em u lsio n : o il = 2 : 1; m ax. em u lsio n p ressu re 600 bar, m ax. vo lu m et ric flo w 20 l s, an d an em u lsio n t an k. A 200 kW m o t o r an d a p u m p in t h e m ain p ress d rive syst em are u sed t o d rive t h e p ressu re in t en sifier. 191 Deep draw ing and stretch draw ing female die blank blank holder punch pressure medium 1 2 3 Fig. 4.2.12 Die layout and production process for active hydro- mechanical draw ing Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th e q u ick d ie ch an ge syst em co n sist s o f q u ick-act io n clam p in g ele- m en t s an d a d ie eject io n syst em , an d p erm it s t o ach ieve m in im u m set - u p t im es. Th e blan k h o ld er base p lat e, fem ale d ie an d p u n ch are clam p ed u sin g fast h yd rau lic clam p in g elem en t s. Th e eject io n syst em t ran sp o rt s t h e base p lat e fro m t h e m ach in e t o get h er wit h t h e d ie. Th e d ie – co m p risin g t h e blan k h o ld er, fem ale d ie an d p u n ch – is lift ed fro m t h e base p lat e an d exch an ged . Th e Hyd ro -Mec t erm in als are lo cat ed in t h e base p lat e. Th ese are au t o m at ically co u p led by m ean s o f a d o ckin g syst em d u rin g in ward t ravel in t o t h e p ress. Advantages of the Active Hydro-Mec process Th e Act ive Hyd ro -Mec p ro cess is ch aract erized by a n u m ber o f sp ecial feat u res wh ich d ist in gu ish it fro m co n ven t io n al p ro d u ct io n . Q u alit y ben efit s in clu d e t h e im p ro ved co m p o n en t st abilit y an d bu cklin g resis- t an ce m ad e p o ssible by t h e p re-st ret ch in g p ro cess d escribed abo ve. Sim ilar t o co n ven t io n al h yd ro -m ech an ical d rawin g p ro cesses, t h e sh eet m et al d o es n o t ru b again st t h e p u n ch o r fem ale d ie bu t is p ressed 192 Sheet metal forming and blanking Fig. 4.2.13 An Active Hydro-M ec press blank holder cylinder stroke limiter active Hydro-M ec die slide slide cylinders Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 again st t h e p u n ch by t h e em u lsio n . At t h e sam e t im e t h e p ro cess en su res o p t im u m su rface q u alit y o f t h e o u t er skin . Du e t o t h e lo wer sh eet m et al t h ickn esses u sed an d t h e elim in at io n o f rein fo rcem en t s, t h e o verall assem bly weigh t can be red u ced . An o t h er ben efit in p ro cess en gin eerin g t erm s is t h e abilit y t o p ro cess d ifferen t m at erials st eel, alu - m in iu m , h igh -st ren gt h st eels an d sh eet t h ickn esses u sin g a sin gle set o f d ies. In ad d it io n , t h e Act ive Hyd ro -Mec p ro cess rep resen t s a co st savin g o ver co n ven t io n al p ro d u ct io n m et h o d s. To o lin g co st s, in p art icu lar, can be red u ced by u p t o 50 , as o n ly o n e h alf o f t h e d ie n eed s t o be m ach in ed t o h ave t h e p art geo m et ry. Fu rt h erm o re, d ies ach ieve a far lo n ger service life d u e t o t h e lo wer d ie wear in vo lved in t h e h yd ro - m ech an ical d rawin g m et h o d . Dep en d in g o n t h e p art co n t o u r an d t h e d esign o f t h e d ie, it is o ft en p o ssible t o save a co m p let e p ro cessin g st ep . 193 Deep draw ing and stretch draw ing Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 4 Sheet metal forming and blanking

4.3 Coil lines