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
Th e deform ation dep th , wh ich dep en ds on th e slide p osition , is deter- m in ed in h ydrau lic p resses by th e switch over p oin t at th e bottom dead
cen ter BDC Fig. 3.3.1
. Dep en din g on sp eed, th e slide travels p ast th is switch over p oin t by a few m illim eters. However, rep eatability rem ain s
with in close lim its, m ean in g th at th e slide is reversed at th e BDC with su f- ficien t accu racy for m ost form in g op eration s. However, if a toleran ce of
less th an 1 m m is req u ired, a m ech an ical stroke lim itation is called for. In com bin ation with a h ydrau lic dam p in g system , th is can ach ieve a m arked
redu ction in th e blan kin g sh ock in volved in p resswork Fig. 3.3.7
. Th ere
82
Fundamentals of press design 250 bar
off center die force
Fig. 3.3.6 Full-stroke parallel control of the press slide
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
are t wo variat io n s in u se. St an d ard d am p in g is u sed fo r m at erial t h ick- n esses exceed in g 3 m m an d fo r ligh t blan kin g wh ich o n ly u t ilizes so m e
30 o f t h e p ress cap acit y – fo r exam p le t rim m in g t h e ed ge o f a wo rk- p iece in a t ran sfer p ress. W h ere h igh -st ren gt h m at erials an d sh eet t h ick-
n esses belo w 3 m m are in vo lved , a p re-t en sio n ed d am p in g syst em is req u ired , sin ce t h is is cap able o f abso rbin g t h e en ergy released in st an -
t an eo u sly at t h e m o m en t o f m at erial sep arat io n .
3.3.5 Slide locking
W h en swit ch in g o ff t h e p ress an d wh en wo rkin g in t h e d ie m o u n t in g area, t h e slid e m u st be reliably safegu ard ed by a slid e lo ckin g d evice.
Germ an accid en t p reven t io n legislat io n UVV 11.064 §12 sp ecifies t h at h yd rau lic p resses wit h a bed d ep t h o f m o re t h an 800 m m an d a
st ro ke len gt h o f m o re t h an 500 m m m u st be eq u ip p ed wit h at least o n e fixt u re act in g o n t h e u p p er en d p o sit io n o f t h e slid e. Th is fixt u re m u st
83
Hydraulic presses
Fig. 3.3.7 Stroke limiting and damping device
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
p reven t t h e slid e fro m d ro p p in g u n d er it s o wn weigh t wh en t h e co n t ro l syst em is swit ch ed o ff. Th e locking device at the top dead center TDC is a
p o sit ive-act in g lo ckin g d evice at t h e u p p er p o in t o f t h e n o m in al st ro ke. A bo lt gu id ed in t h e p ress fram e is p u sh ed by a h yd rau lic p ist o n in t o a
recess in t h e slid e Fig. 3.3.8
. Th e bo lt is co n figu red t o carry all m o vin g weigh t s, in clu d in g t h at o f t h e d ie su p erst ru ct u re.
Th e infinitely variable locking device is a n o n -p o sit ive act in g slid e safe- gu ard in wh ich a ret ain in g ro d at t h e slid e is gu id ed by t h e clam p in g
h ead in t h e p ress cro wn Fig. 3.3.9
. Th e p ilo t jaws h o ld t h e m o vable elem en t s in an y p o sit io n – even in case o f a p o wer failu re. Th is lo ckin g
d evice, wh ich is arran ged in t h e slid e area, is reco m m en d ed p art icu lar- ly in p resses feat u rin g a blan k h o ld er an d in t ern al slid e. Th e slid e can be
fixed in an y p o sit io n , elim in at in g t h e n eed fo r a sep arat e safet y d evice fo r t h e blan k h o ld er.
84
Fundamentals of press design
Fig. 3.3.8
Positive acting slide locking device bolt
locking cylinder housing
slide
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
85
Hydraulic presses
Fig. 3.3.9
Non-positive acting locking device for the blank holder and the draw ing slide upright
slide gib rail
press crown
rod fixture clamping head
retaining rod
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
3 Fundamentals of press design
3.4 Changing dies 3.4.1 Die handling
