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
Th e m ajo r p n eu m at ic fu n ct io n s o f m ech an ical p resses are t h e clu t ch , brake, flywh eel brake, slid e co u n t erbalan ce, slid e cu sh io n an d bed
cu sh io n . In t h e case o f t ran sfer p resses, p n eu m at ic fu n ct io n s also in clu d e t h e ap p licat io n o f air p ressu re t o t h e t ran sfer cam fo llo wers an d
t ran sp o rt by su ct io n cu p s. Large vo lu m es o f air req u ire co m p ressed air t an ks wit h a m o n it o rin g safet y fu n ct io n an d d rain age syst em . Th e m ax-
70
Fundamentals of press design
eccentric eccentric bushing
inner tapered ring outer tapered ring
clamping screw central bore for
pressure medium
connecting rod grooves for
pressure medium
Fig. 3.2.13
Continuous stroke adjustment in an eccentric press
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
im u m p n eu m at ic p ressu re is gen erally 6 bar, alt h o u gh h igh -p ressu re n et wo rks o r co m p resso rs p ro d u cin g a m axim u m o f 16 bar are in creas-
in gly em p lo yed . Th e en gin eerin g o f t h ese au xiliary u n it s is d et erm in ed by valid st an -
d ard s an d legal req u irem en t s. In gen eral, galvan ized gas lin es bet ween 1 an d 6 are u sed fo r in st allat io n p u rp o ses. Sm aller lin es are co n figu red
u sin g st eel p ip in g an d cu t t in g rin g o r bead ed u n io n s. Th e in st allat io n req u ired fo r a large-p an el t ran sfer p ress wit h a st ru ct u ral vo lu m e o f
aro u n d 40 3 10 3 15 m can co m p rise u p 40 t , in clu d in g co m p ressed air t an k, p ip es an d ap p lian ces.
3.2.10 Hydraulic system
Th e u se o f h yd rau lics in m ech an ical p ress co n st ru ct io n is relat ively m in im al. St an d ard u se o f h yd rau lic en gin eerin g in t h is t yp e o f p ress is
rest rict ed t o t h e h yd rau lic o verlo ad safegu ard , raisin g t h e m o vin g bo l- st er an d h yd rau lic d ie clam p in g syst em s. All t h ese fu n ct io n s are gen er-
ally su p p lied fro m a cen t ral h yd rau lic u n it . In t h e case o f t ran sfer p ress- es, t h ese basic fu n ct io n s are co m p lem en t ed by o t h er fu n ct io n s su ch as
en gagem en t o f t h e clu t ch bet ween t h e p ress an d t ran sfer d rive syst em s an d t h e co m p reh en sive syst em o f scrap eject io n flap s. In ad d it io n , var-
io u s clam p in g an d lo ckin g d evices aro u n d t h e p ress are h yd rau lically d riven .
Th e m o st im p o rt an t fu n ct io n in m ech an ical p resses, en gagin g an d brakin g t h e slid e d rive syst em , is bein g in creasin gly d o n e by h yd rau lic
m ean s. Th e u se o f h yd rau lics p erm it s h igh er swit ch in g freq u en cies in sin gle p resses an d is also m o re en viro n m en t ally frien d ly in t erm s o f
n o ise an d air p o llu t io n . Th e clu t ch an d brake are su p p lied by a cen t ral h yd rau lic u n it
eq u ip p ed wit h a co o lin g syst em . A d u al-ch an n el safet y co n t ro l wit h regu lat ed d am p in g facilit y an d p ressu re filt rat io n t o 10 µ m is req u ired .
Th e in creased u se o f d eep d rawin g wit h sin gle-act in g p resses p laces p art icu larly st rin gen t d em an d s o n t h e blan kh o ld in g fu n ct io n an d t h u s
t h e d raw cu sh io n in t h e p ress bed cf. Sect . 3.1.4
, p art icu larly in large- p an el p resses. Mu lt ip le-p o in t bed cu sh io n s wit h p ressu re co n t ro l cap a-
bilit y are t h en o n ly p o ssible u sin g a co m p lex servo h yd rau lic syst em .
71
M echanical presses
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Th is req u ires sep arat e su p p ly u n it s wit h o il t an k, p u m p o u t p u t s o f ap p ro x. 150 kW an d o il flo w rat es o f ap p ro x. 1,000 l m in fo r t h e d raw
cu sh io n . Co n t ro l is p erfo rm ed u sin g p ro p o rt io n al valves co m p lyin g t o DIN an d ISO st an d ard s in t h e p ressu re ran ge u p t o 300 bar.
3.2.11 Lubrication
