Types of drive system

over sm all d istan ces, for in stan ce d u rin g blan kin g or coin in g. Th e great d an ger is th at su ch overload in g m ay go u n d etected . For th is reason , over- loading safety devices m u st be u sed to p rotect th e p ress cf. Sect. 3.2.8 . An o t h er fo rm o f o verlo ad in g resu lt s fro m t akin g t o o m u ch en ergy fro m t h e flywh eel. Su ch o verlo ad in g can resu lt in ext rem ely h igh p ress fo rces if t h e d isp lacem en t d u rin g d efo rm at io n is t o o sm all. Ho wever, if t h e en ergy is ap p lied o ver a large d isp lacem en t , t h is t yp e o f o verlo ad is m u ch less d an gerou s. For exam p le, if th e p ress d escribed above is brou gh t to a stop d u rin g a workin g d istan ce of h = 100 m m , th e en tire flywh eel en ergy of W = 15,600 Nm is u tilized . Assu m in g th at n o p eak load s h ave occu rred , th e m ean p ress force exerted is on ly Th e p ress is th erefore by n o m ean s overloaded alth ou gh th e flywh eel h as been brou gh t to a stan dstill. In th is case, on ly th e drive m otor su ffers a very large slowdown an d it is n ecessary to u se a p ress of a larger flywh eel en ergy cap acity, alth ou gh th e p erm issible p ress force of 1,000 kN is m ore th an adeq u ate. Overloads of th is typ e occu r m ore freq u en tly if deform ation is don e over a large distan ce, e. g. du rin g deep drawin g, op en or closed die extru sion .

3.2.2 Types of drive system

Eccentric or crank drive Fo r a lo n g t im e, eccen t ric o r cran k d rive syst em s were t h e o n ly t yp e o f d rive m ech an ism s u sed in m ech an ical p resses. Th e sin u so id al slid e d is- p lacem en t o f an eccen t ric p ress is seen in Fig.3.2.3. Th e relat ively h igh im p act sp eed o n d ie clo su re an d t h e red u ct io n o f slid e sp eed d u rin g t h e fo rm in g p ro cesses are d rawbacks wh ich o ft en p reclu d e t h e u se o f t h is t yp e o f p ress fo r d eep d rawin g at h igh st ro kin g rat es. However, in p resses with cap acities u p to a n om in al force of 5,000 kN, su ch as u n iversal or blan kin g p resses, eccen tric or cran k d rive is still th e m ost effective d rive system . Th is is esp ecially tru e wh en u sin g au tom at- ed system s wh ere th e eccen tric d rive offers a good com p rom ise between tim e n ecessary for p rocessin g an d th at req u ired for p art tran sp ort. Even in th e latest crossbar tran sfer p resses, eccen tric d rive system s u sed in 54 Fundamentals of press design F W h Nm m N kN = = = = , . , 15 600 0 1 156 000 156 Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 su bseq u en t p rocessin g station s, after th e d rawin g station , satisfy th e req u irem en ts for system sim p lification . Stroke len gth s of u p to 1,300 m m are ach ieved u sin g eccen t ric gears wit h a d iam et er o f 3,000 m m . Th e eccen t ric gears are m an u fact u red fro m d u ct ile iro n in acco rd an ce wit h t h e h igh est q u alit y st a n d ard s cf. Sect . 3.7 . Linkage drive Req u irem en t s fo r im p ro ved eco n o m y lead d irect ly t o h igh er st ro kin g rat es. W h en u sin g cran k o r eccen t ric d rive syst em s, t h is in vo lves in creasin g t h e slid e sp eed . Ho wever, wh en p erfo rm in g d eep -d rawin g wo rk, fo r t ech n ical reaso n s t h e ram sp eed sh o u ld n o t exceed 0.4 t o 0.5 m s d u rin g d efo rm at io n . Th e lin kage d rive syst em can be d esign ed su ch t h at in m ech an ical p resses, t h e slid e sp eed d u rin g t h e d rawin g p ro cess can be red u ced , co m p ared t o eccen t ric d rive by bet ween a h alf an d a t h ird Fig. 3.2.3 . Th e slid e in a d o u ble-act in g d eep d rawin g p ress, fo r exam p le, is act u at ed u sin g a sp ecially d esign ed lin kage d rive Fig. 3.2.4 an d cf. Fig. 3.1.8 . 55 M echanical presses Fig. 3.2.3 Displacement-time diagram: comparison of the slide motion performed by an eccentric, a knuckle-joint and a link-driven press 90 180 270 360 bottom dead center BDC crank angle[ 100 200 300 400 500 600 700 900 eccentric drive system eight-link drive system modified knuckle-joint drive system six-link drive system st ro ke [m m ] 800 approx. 180 approx. 170 approx.110 Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th is kin em at ic ch aract erist ic o ffers id eal co n d it io n s fo r t h e d eep - d rawin g p ro cess. Th e slid e h it s t h e blan k so ft ly, allo win g t o bu ild u p h igh p ress fo rces righ t fro m t h e st art o f t h e d rawin g p ro cess, an d fo rm s t h e p art at a lo w, alm o st co n st an t sp eed . In ad d it io n , t h is syst em en su res sm o o t h t ran sit io n s bet ween t h e vario u s p o rt io n s o f t h e slid e m o t io n . Du rin g d efo rm at io n , t h e d rive lin ks are st ret ch ed t o an alm o st ext en d ed p o sit io n . Th u s, t h e clu t ch t o rq u e, t h e gear lo ad an d t h e d ecel- erat in g an d accelerat in g gear m asses are bet ween 20 an d 30 sm aller t h an in a co m p arable eccen t ric p ress. In t h e case o f sin gle-act in g m ach in es, fo r in st an ce, red u cin g t h e im p act in creases t h e service life o f t h e d ies, t h e d raw cu sh io n an d t h e p ress it self. 56 Fundamentals of press design Fig. 3.2.4 Slide eight-link drive system and blank holder slide drive toggle joint drive system in a double-acting deep draw ing press Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th is o ffers a n u m ber o f im p o rt an t ben efit s in p ro d u ct io n : fo r t h e sam e n o m in al p ress fo rce an d t h e sam e n o m in al slid e st ro ke, a lin k- d riven p ress can be lo ad ed su bst an t ially earlier in t h e st ro ke, becau se t h e p ress fo rce d isp lacem en t cu rve is st eep er wit h in t h e d efo rm at io n ran ge. Th erefo re, t h e lin kage p ress h as a m o re favo rable fo rce-d isp lace- m en t cu rve t h an o n an eccen t rically-d riven p ress Fig. 3.2.2 . Wit h o u t in creasin g t h e im p act sp eed , it is p o ssible t o ach ieve an ap p reciable in crease in t h e st ro kin g rat e an d o u t p u t . Du e t o t h e im p ro ved d rawin g co n d it io n s, a h igh er d egree o f p ro d u ct q u alit y is ach ieved ; even sh eet m et al o f an in ferio r q u alit y can be u sed wit h sat isfact o ry resu lt s. In ad d it io n , t h is syst em red u ces st ress bo t h o n t h e d ie an d t h e d raw cu sh - io n an d also o n t h e clu t ch an d brake. Fu rt h erm o re, n o ise em issio n s are red u ced as a resu lt o f t h e lo wer im p act sp eed o f t h e slid e an d t h e q u iet er h errin gbo n e gears o f t h e d rive wh eels. In t h e case o f large-p an el t ran sfer p resses, t h e u se o f six o r eigh t - elem en t lin kage d rive syst em s is largely d et erm in ed by d efo rm at io n co n d it io n s, t h e p art t ran sp o rt m o vem en t an d t h e o verall st ru ct u re o f t h e p resses. As a resu lt , in t h e case o f t ran sfer p resses wit h t ri-axis t ran sfer syst em , a six-elem en t lin kage d rive syst em is freq u en t ly u sed , sin ce t h is rep resen t s t h e best p o ssible co m p ro m ise bet ween o p t im u m p ress geo m et ry an d m an u fact u rin g co st s cf. Sect . 4.4.7 . In t h e case o f cro ssbar t ran sfer p resses, eit h er an eigh t -elem en t lin kage d rive o r a co m bin at io n o f lin kage an d eccen t ric d rives are u sed in o rd er t o o p t i- m ize t h e d ie-sp ecific t ran sfer m o vem en t s cf. Sect . 4.4.8 . Th e lin kage elem en t s are m ad e o f d u ct ile iro n , t h e lin kage p in s are fro m st eel wit h h ard en ed co n t act su rfaces an d t h e bearin g bu sh es are fro m h igh ly st ress-resist an t n o n -ferro u s allo ys. A reliable syst em o f lu brica- t io n an d o il d ist ribu t io n gu aran t ees safe o p erat io n o f t h ese h igh ly st ressed bearin gs cf. Sect . 3.2.11 . Knuckle-joint drive system Th is d esign p rin cip le is ap p lied p rim arily fo r co in in g wo rk. Th e kn u ck- le-jo in t d rive syst em co n sist s o f an eccen t ric o r cran k m ech an ism d ri- vin g a kn u ckle-jo in t . Figure 3.2.5 sh o ws t h is co n cep t u sed in a p ress wit h bo t t o m d rive. Th e fixed jo in t an d bed p lat e fo rm a co m p act u n it . Th e lo wer jo in t m o ves t h e p ress fram e. It act s as a slid e an d m o ves t h e at t ach ed t o p d ie u p an d d o wn . Du e t o t h e o p t im u m fo rce flo w an d t h e favo rable co n figu rat io n p o ssibilit ies o ffered by t h e fo rce-t ran sm it t in g 57 M echanical presses Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 elem en t s, a h igh ly rigid d esign wit h very lo w d eflect io n ch aract erist ics is ach ieved . Th e kn u ckle-jo in t , wit h a relat ively sm all co n n ect in g ro d fo rce, gen erat es a co n sid erably larger p ressin g fo rce. Th u s, wit h t h e sam e d rive m o m en t , it is p o ssible t o reach aro u n d t h ree t o fo u r t im es h igh er p ressin g fo rces as co m p ared t o eccen t ric p resses. Fu rt h erm o re, t h e slid e sp eed in t h e regio n 30 t o 40° abo ve t h e bo t t o m d ead cen t er, is ap p reciably lo wer cf. Fig. 6.8.3 . Bo t h d esign feat u res rep resen t a p ar- t icu lar ad van t age fo r co in in g wo rk cf . Fig. 6.8.21 o r in h o rizo n t al p res- ses fo r so lid fo rm in g cf. Fig. 6.8.7 . By in sert in g an ad d it io n al jo in t , t h e kin em at ic ch aract erist ics an d t h e sp eed versu s st ro ke o f t h e slid e can be m o d ified . Kn u ckle-jo in t an d m o d ified kn u ckle-jo in t d rive syst em s can be eit h er t o p cf. Fig. 4.4.10 58 Fundamentals of press design flyw heel press frame housing connecting rod crankshaft fixed press bed knuckle-joint Fig. 3.2.5 Knuckle-joint press w ith bottom drive Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 o r bo t t o m m o u n t ed . Fo r so lid fo rm in g, p art icu larly, t h e m o d ified t o p d rive syst em is in p o p u lar u se. Figure 3.2.6 illu st rat es t h e p rin cip le o f a p ress co n figu red acco rd in g t o t h is sp ecificat io n . Th e fixed p o in t o f t h e m o d ified kn u ckle-jo in t is m o u n t ed in t h e p ress cro wn . W h ile t h e u p p er jo in t p ivo t s aro u n d t h is fixed p o in t , t h e lo wer jo in t d escribes a cu rve- sh ap ed p at h . Th is resu lt s in a ch an ge o f t h e st ro ke versu s t im e ch arac- t erist ic o f t h e slid e, co m p ared t o t h e largely sym m et rical st ro ke-t im e cu rve o f t h e eccen t ric d rive syst em Fig. 3.2.3 . Th is cu rve can be alt ered by m o d ifyin g t h e arran gem en t o f t h e jo in t s o r p o ssibly by in t egrat in g an ad d it io n al jo in t . As a ru le, it is d esirable t o red u ce t h e slid e velo cit y d u rin g d efo rm a- t io n e. g. red u ct io n o f t h e im p act an d p ressin g sp eed o f t h e slid e. Usin g t h is p rin cip le, t h e slid e d isp lacem en t available fo r d efo rm at io n can be in creased t o be t h ree o r fo u r t im es great er t h an wh en u sin g eccen t ric p resses wit h a co m p arable d rive t o rq u e. Th is rep resen t s a fu r- t h er ad van t age wh en fo rm in g fro m so lid cf. Linkage drive. 59 M echanical presses flyw heel drive shaft eccentric drive system press slide slide adjustment motion curve, point B B Fig. 3.2.6 M odified knuckle- joint drive system Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th e blan k h o ld er d rive, so m et im es u sed in d o u ble-act in g d eep d raw p resses, is a sp ecial case Fig. 3.2.4 an d cf. Fig. 3.1.8 . Th e req u ired st an d - st ill o f t h e blan k h o ld er d u rin g t h e d eep -d rawin g p h ase is ach ieved in t h is t yp e o f m ach in e by su p erim p o sin g a d o u ble kn u ckle-jo in t syst em co u p led wit h t h e eccen t ric o r lin kage d rive o f t h e slid e. Th e st an d st ill o f t h e blan k h o ld er rep resen t s a cran k an gle o f bet ween 90 an d 130° wit h a m axim u m resid u al m o vem en t o f 0.5 m m . Th is resid u al m o vem en t d o es n o t , h o wever, in flu en ce t h e d eep -d rawin g p ro cess becau se t h e blan k h o ld er o verlo ad safegu ard act s as a st o rage syst em an d t h e elast ic d eflect io n o f t h e en t ire p ress, wh ich is a few m illim et ers, h as an o ver- rid in g effect . Th e slid e d rive, t h e blan k h o ld er d rive an d t h e wh eel gear are in t egrat ed in t h e p ress cro wn .

3.2.3 Drive motor and flyw heel