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
In larger-scale p resses, t h e m ain d rive syst em is u su ally p o wered by DC m o t o rs, p rim arily in o rd er t o p ro vid e a large st ro kin g rat e. Freq u en cy-
co n t ro lled t h reep h ase m o t o rs o ffer an alt ern at ive, p art icu larly wh ere a h igh p ro t ect io n class rat in g is called fo r. Th e o u t p u t o f a p ress, wh ich is
d et erm in ed by fo rce, slid e d isp lacem en t an d sp eed , in clu d in g lo st en er- gy, is p ro vid ed by t h e m ain m o t o r. Perio d ically o ccu rrin g lo ad p eaks are
co m p en sat ed by t h e flywh eel wh ich st o res en ergy. Th e h igh ly elast ic DC d rive syst em is able t o co m p en sat e fo r a d ro p o f t h e flywh eel sp eed
o f u p t o 20 in every p ress st ro ke an d t o rep lace t h e co n su m ed en ergy by accelerat io n o f t h e flywh eel p rio r t o t h e su bseq u en t st ro ke.
Usefu l en ergy sh o u ld also be available d u rin g set -u p o p erat io n wit h a red u ced st ro kin g rat e, fo r exam p le five st ro kes p er m in u t e. In t h is case,
a sp eed d ro p o f 50 is ad m issible. An im p o rt an t crit erio n in co n figu r- in g t h e en ergy balan ce is t o en su re a sh o rt ru n -u p t im e. Ru n n in g u p
a large-p an el p ress fro m it s m in im u m t o it s m axim u m p ro d u ct io n st ro kin g rat e gen erally t akes less t h an o n e m in u t e u n d er lo ad .
Du e t o t h e req u ired u sefu l en ergy an d t h e p erm issible flywh eel slo w- d o wn o f 20 , t h e flywh eel is gen erally d esign ed t o o p erat e u n d er t h e
m o st en ergy-co n su m in g co n d it io n , i. e. in t h e lo wer st ro kin g ran ge o f t h e p ress. Alt h o u gh a h igh flywh eel sp eed is ben eficial h ere, t h is is lim -
it ed by t h e ad m issible sp eed o f t h e clu t ch , brake an d flywh eel it self.
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Fundamentals of press design
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
In cro ssbar t ran sfer p resses, flywh eels o f u p t o 2,500 m m in d iam et er an d a weigh t o f 25 t are u sed . Th e m o u n t in g an d lu bricat io n o f t h is
t yp e o f flywh eel in ro ller bearin gs are h igh ly d em an d in g, as a large q u an t it y o f lu brican t an d co n t in u o u s t em p erat u re m o n it o rin g are
req u ired cf. Sect. 3.2.11
. Th e flywh eel is d riven by t h e m ain m o t o r via a flat belt o r h igh -p erform an ce V-belt. W h en t h e m ain d rive system is
swit ch ed o ff, t h e flywh eel is brou gh t to a stan d st ill wit h in a m axim u m o f 30 s by reverse brakin g of th e m otor an d by an ad d it io n al p n eu m atic
brake. In iso lat ed cases, n o rm al car bo d y p resses an d t ri-axis t ran sfer p resses
are eq u ip p ed wit h m ech an ical creep sp eed d rive syst em s o f o n e st ro ke p er m in u t e. In t h is case, t h e d rive is ach ieved by a t h reep h ase m o t o r
act in g o n a wo rm gear wh ich act u at es t h e d rive sh aft via t h e brake flan ge o f t h e m ain brake. Th e t ran sm it t ed t o rq u e gen erally falls sh o rt o f
t h e n o m in al d rive t o rq u e. Ho wever, by m ean s o f a p n eu m at ic o r h yd rau lic servo syst em in t h e brake, t h e n o m in al fo rce m ay be ach ieved
fo r d ist an ces o f u p t o 10 m m . Th is is gen erally su fficien t fo r set -u p o p erat io n .
3.2.4 Clutch and brake
