Parallelism of the slide

– t h eir n at u re in evit ably resu lt s in a st an d ard izat io n p ro cess: t h e valve blo cks d o n o t n eed t o be red esign ed fo r each d ifferen t p ress, – all t h e valves are bro u gh t t o get h er t o creat e a fu n ct io n al assem bly o n a sin gle blo ck, – in t egrat ed valves are sen sibly co m bin ed wit h sp ace-savin g, lo w-co st au xiliary valves, – t ro u blesh o o t in g is sim p lified by t h e p resen ce o f d rilled -in fu n ct io n al an d t est co n n ect io n s.

3.3.3 Parallelism of the slide

Th e cap acit y o f t h e p ress fram e t o abso rb eccen t ric lo ad s p lays a m ajo r ro le. Eccen t ric fo rces o ccu r d u rin g t h e fo rm in g p ro cess wh en t h e lo ad o f t h e resu lt in g d ie fo rce is n o t exert ed cen t rally o n t h e slid e, cau sin g it t o t ilt Fig. 3.3.5 . Th e st an d ard p ress is able t o abso rb a m axim u m eccen - t ric m o m en t o f lo ad o f via th e slid e gibs. Th is resu lts in a m axim u m slid e tilt of 0.8 m m m . If a h igh er off cen ter load in g cap ability is d esired , th en th e p ress d esign m u st be m ore rigid . In th is case, th e slid e gibs will h ave greater stability, th e p ress fram e will be m ore rigid , an d th e slid e will be h igh er. If it is n o t eco n o m ically p o ssible t o ach ieve t h e allo wable am o u n t o f slid e t ilt wit h in t h e req u ired lim it s by in creasin g p ress rigid it y, it is n ec- essary t o u se h yd rau lic p arallelism co n t ro l syst em s, u sin g elect ro n ic co n t ro l t ech n o lo gy Fig. 3.3.5 , fo r exam p le in t h e case o f h yd rau lic t ran sfer p resses cf. Fig. 4.4.14 . T he parallelism control system s act in t h e d ie m o u n t in g area t o co u n t er slid e t ilt . Po sit io n m easu rem en t sen so rs m o n it o r t h e p o sit io n o f t h e slid e an d act ivat e t h e p arallelism co n t ro l syst em Fig. 3.3.5 . Th e p arallelism co n t ro llin g cylin d ers act o n t h e co r- n ers o f t h e slid e p lat e an d t h ey are p u sh ed d u rin g t h e fo rm in g p ro cess again st a cen t rally ap p lied p ressu re. If t h e elect ro n ic p arallelism m o n i- t o r sen so r d et ect s a p o sit io n erro r, t h e p ressu re o n t h e lead in g sid e is in creased by m ean s o f servo valves, an d at t h e sam e t im e red u ced o n t h e o p p o sit e sid e t o t h e sam e d egree. Th e su m o f exert ed p arallelism 80 Fundamentals of press design M m F kNm M M kNm x N y x = ⋅ [ ] = [ ] 0 075 2 . Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 co n t ro l fo rces rem ain s co n st an t , an d t h e slid e t ilt balan ce is rest o red . Dep en d in g o n t h e d efo rm at io n sp eed , a slid e p arallelism o f 0.05 t o 0.2 m m m is ach ieved . A cen t ral d evice ad ju st s t h e syst em t o d ifferen t d ie h eigh t s by m ean s o f sp in d les at t h e slid e. Full-stroke parallelism control in volves th e u se of p arallel con trol cylin - d ers, with th eir p iston s p erm an en tly con n ected to th e slid e Fig. 3.3.6 . Th ese act over th e en tire stroke of th e slid e so th at n o settin g sp in d les are req u ired to ad ju st th e workin g stroke. Two cylin d ers with th e sam e su rface area, arran ged well ou tsid e th e cen ter of th e p ress, are su bjected to a m ean p ressu re. Th e ten sile an d com p ressive forces are balan ced ou t by m ean s of d iagon al p ip e con n ection s. Th e system is n eu tral in term s of force exerted on th e slid e. If an off-cen ter load is exerted by th e d ie on th e slid e, a tilt m om en t is gen erated . Th e slid e p osition sen sor d etects a d eviation from p arallel an d triggers th e servo valve. Th e valve in creases th e p ressu re on th e u n d ersid e of th e p iston actin g on th e lead in g sid e of th e slid e, an d th u s also on th e op p osite u p p er sid e of th e p iston . At th e sam e tim e, th e p ressu re in th e oth er con n ectin g p ip e is red u ced . Th e 81 Hydraulic presses Fig. 3.3.5 Control system for maintaining slide parallelism I P I P F = F + F w ith F = F + F 1 2 3 3 4 5 F 4 F 5 F 1 F 2 slide tilt pressing force parallelism control displacement monitoring slide stroke F min center of die force 250 bar F max x y a b Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 o p p o sin g su p p o rt in g t o rq u es exert ed o n t h e t wo sid es co u n t eract t h e t ilt m o m en t . Th e m axim u m d eviat io n m easu red at t h e p arallel co n t ro l cylin d ers is bet ween 0.6 an d 0.8 m m d u rin g d rawin g, ben d in g an d fo rm in g o p erat io n s.

3.3.4 Stroke limitation and damping