Slide and blank holder

3.2.7 Press crow n assembly

Th e co n n ect in g ro d , lin ks, gears an d m ain d rive syst em d et erm in e t h e cap acit y an d t h e size o f t h e p ress cro wn . Th e weld ed co m p o n en t s weigh u p t o 150 t , as d o t h e m o u n t ed gear d rive elem en t s co n t ain ed in t h e cro wn o f a large-p an el p ress. Th e d im en sio n al lim it s o f su ch large-scale p art s are aro u n d 6,000 3 3,600 3 12,000 m m , wh ereby wid t h , h eigh t an d weigh t d ep en d o n t h e p o ssibilit ies o ffered fo r ro ad t ran sp o rt o n lo w-bed t ru cks – wh ich gen - erally req u ire sp ecial au t h o rizat io n . Wat erways rep resen t a less d ifficu lt m et h o d o f t ran sp o rt in g t h is t yp e o f co m p o n en t s. St ress-relief an n ealin g o f large weld ed assem blies an d also m ach in in g on d rillin g cen ters is restricted to a m axim u m len gth of 12 m . Th e en tire p ro blem o f t ran sp o rt lo gist ics p lays a m ajo r ro le in large-p an el p ress d esign an d m u st be t aken in t o co n sid erat io n righ t fro m t h e p lan n in g st age.

3.2.8 Slide and blank holder

Th e ro t ary m o t io n gen erat ed by t h e p ress d rive is t ran sm it t ed t o t h e lin ear m o t io n o f t h e slid e an d blan k h o ld er u sin g a su it able sp eed an d fo rce p ro gressio n . Th e m o st im p o rt an t fu n ct io n al u n it s, p art icu larly in large-p an el p resses, are t h e pressure points co n t ain in g slid e ad ju st m en t an d an o verlo ad safet y d evice. Slide adjustm ent In in d ivid u al p resses, p ressu re p o in t s wit h a slid e ad ju st m en t o f u p t o 600 m m are u sed in t h e m ain sp in d le in o rd er t o ad ju st t h e p ress sh u t h eigh t t o vario u s d ie h eigh t s Fig. 3.2.10 . In u n iversal an d t ran sfer p resses, slid e ad ju st m en t d ist an ces o f 150 m m are su fficien t . In t h is case, p ressu re p o in t s wit h a lo w o verall h eigh t are u sefu l. Usin g brake m o t o rs an d wo rm gears, ad ju st in g sp eed s o f 60 m m m in are o bt ain ed . Wit h m u lt ip le-st age p resses u sed fo r so lid fo rm in g, t o ach ieve h igh st iff- n ess, wed ge ad ju st m en t s are freq u en t ly u sed in t h e d ie set o r at t h e slid e clam p in g p lat e. In t h is case, a slid e ad ju st m en t is n o lo n ger n ecessary. 66 Fundamentals of press design Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Overload safety devices Th e n o m in al fo rce o f t h e p ress is lim it ed an d safegu ard ed by t h e h yd rau lic o verlo ad safet y d evice in t h e slid e. If t h e n o m in al p ress fo rce is exceed ed , t h e p ressu re exert ed o n a h yd rau lic cu sh io n in t egrat ed in t h e p ressu re p o in t is q u ickly relieved , allo win g an o verlo ad d isp lace- m en t . For blan k h old ers u sed in d ou ble-actin g m ech an ical p resses, th e over- lo ad safet y fu n ct io n is co u p led t o t h e ad ju st m en t fu n ct io n o f t h e blan k h o ld er fo rce. Th e o verlo ad safet y fu n ct io n is act ivat ed o n ly wh en t h e d eflect io n o f t h e fo u r blan k h o ld er p ressu re p o in t s h as exceed ed a p er- m issible m agn it u d e o f ap p ro x. 3 m m . Th e safet y fu n ct io n is act u at ed by an air-h yd rau lic p ressu re scale. By ch an gin g t h e co m p ressed air set t in g, t h e blan k h o ld er fo rce can be ad ju st ed t o t h e req u irem en t s o f t h e d ie at t h e fo u r p ressu re p o in t s wit h in a ran ge o f 40 t o 100 . Slide counterbalance Th e slid e weigh t is com p en sated by th e slid e cou n terbalan ce system . Th u s, th e weigh t of all m ovin g p arts su ch as join ts, con n ectin g rod s, th e slid e an d u p p er d ie, is balan ced ou t by p n eu m atic cylin d ers Fig. 3.2.11 . As a resu lt, th e d rive system is largely free of gravity forces. Th ere are n o stresses actin g on th e slid e ad ju stm en t an d th ere is an ad d i- 67 M echanical presses slide adjustment device connecting rod w rist pin adjustment nut overload bolt oil cushion pressure pad adjustment spindle adjustment device connecting rod w rist pin adjustment nut adjustment pad overload bolt oil cushion Fig. 3.2.10 Spindle left and pressure point right Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 t io n al safegu ard again st d o wn ward t ravel o f t h e slid e cau sed by gravit y. Pn eu m at ic weigh t co m p en sat io n gu aran t ees lo w-n o ise, vibrat io n -free o p erat io n , sm o o t h lo ad in g o f t h e m o t o r an d sh o rt brakin g d ist an ces. Fo r co u n t erbalan cin g weigh t s u p t o 200 t , at 10 bar air p ressu re, cylin d er sizes u p t o a 900 m m d iam et er are req u ired . Lo n g slid e st ro kes o f u p t o 1,300 m m an d p erm issible p ressu re sp ikes o f u p t o 25 req u ire su bst an t ial su rge t an ks. Th e arran gem en t o f cylin d ers an d t an ks d e- p en d s o n t h e t yp e o f p ress an d safet y issu es. In t h e case o f co u n t erbal- an ce cylin d ers wh ich are n o t ext ern ally en clo sed , d o u ble p ist o n ro d s are o ft en req u ired t o safegu ard again st t h e risk o f breakage Fig. 3.2.11 . Co n versely, if t h e syst em is in t egrat ed in t h e p ress cro wn , t h is ad d i- t io n al safet y feat u re is n o t n ecessary. Wit h every d ie ch an ge, t h e weigh t co m p en sat io n syst em m u st be au t o m at ically ad ju st ed t o t h e n ew d ie weigh t s fo r t h is p u rp o se. In d ivid u al p resses are fit t ed wit h sp ecial weigh in g an d co n t ro l fu n c- t io n s. Pro gram -co n t ro lled au t o m at ic syst em s u sed in t ran sfer p resses au t o m at ically set t h e p ro gram in h eren t p ressu re valu e wh en ch an gin g d ies in o rd er t o red u ce set -u p t im es t o a m in im u m . 68 Fundamentals of press design slide breakage sensor tubular rod safety rod piston cylinder compressed air tank Fig. 3.2.11 Compensation of slide speed w ith double piston rod Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Slide cushion So m e u sers o f p resses p refer t o u se slid e cu sh io n s as an eject o r fo r t h e t o p d ie. In t h ese cases, p n eu m at ic bello w cylin d ers are u sed t o su p p ly t h e req u ired eject io n fo rces Fig. 3.2.12 . Here, eject io n st ro kes can be an ywh ere bet ween 100 an d 200 m m , wit h p ressu re in creases o f u p t o 30 . Th e bello w cylin d ers act o n an eject o r p lat e wh ich t ran slat e t h e fo rce t o t h e p ressu re p in s o f t h e cu sh io n an d o f t h e d ie. Du rin g t h e u p st ro ke o f t h e slid e, t h e eject o r p lat e an d t h e p in s are ret u rn ed by fo rce fro m t h e bello w cylin d ers t o t h eir lo west p o sit io n . Dam p in g elem en t s are u sed t o red u ce t h e n o ise resu lt in g fro m t h e h ard im p act . Stroke adjustm ent To d ay, t h e st ro ke o f sm all m ech an ical p resses can be ad ju st ed by m o t o r p o wer continuously acco rd in g t o req u irem en t s o f t h e fo rm ed p art s wit h t h e aid o f t wo in t eract ive eccen t rics Fig. 3.2.13 . Th e st ro ke can , fo r exam p le, be set in su ch a way t h at t h e req u ired p art h eigh t is reach ed d u rin g t h e d eep d rawin g p ro cess an d t h e p art can be rem o ved fro m t h e d ie wit h o u t d ifficu lt ies o n co m p let io n o f t h e d eep -d rawin g o p erat io n . Th e elast ic clam p co n n ect io n bet ween t h e eccen t ric sh aft an d t h e eccen t ric bu sh in g is h yd rau lically released . Th is in vo lves exp an d in g t h e 69 M echanical presses bellow s cylinder damping rail pressure pin, slide cushion pressure pins, die ejector plate, die separate slide plate pressure plate bottom stop slide upper die Fig. 3.2.12 Slide cushion w ith bellow cylinders Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 bu sh in g again st th e clam p so th at it can be rotated u sin g a glid in g m otion in an y d irection on an oil cu sh ion . Sp ecial seals are u sed to p re- ven t oil leakage. Th e p osition of th e eccen trics in relation to each oth er is m od ified from th e con trol d esk in accord an ce with th e sp ecific req u irem en ts of th e d ie u n til th e su m of th e eccen tricities reach es th e req u ired stroke. Th e p ositive con n ection between th e eccen tric sh ells is created as a resu lt of p ressu re relief cou p led with ru n -away of th e oil th rou gh d rain age grooves. For each d ie, it is p ossible to store th e req u ired stroke in th e d ie d ata record . Th is in form ation can be accessed again an d u sed for au tom atic ad ju stm en t of th e slid e stroke.

3.2.9 Pneumatic system