Th e gu id an ce rat io , i. e. t h e rat io o f gu id e len gt h t o slid e len gt h , can be red u ced t o 1 : 3 in large-scale p resses wit h a h eigh t rest rict io n . Eccen -
t ric p ress fo rces can o n ly be p art ially abso rbed by t h e gibs in t h is case. Fo r h o t fo rm in g ap p licat io n s, t h e exp an sio n o f t h e slid e d u e t o t em p er-
at u re m u st be t aken in t o co n sid erat io n in t h e ch o ice o f slid e gibs. In t h is case, gu id an ce syst em s are u sed wh ich p erm it exp an sio n o f t h e
slid e in o n e d irect io n wit h o u t gen erat in g ad d it io n al st resses Fig. 3.1.7
. Fo r eject io n o f p art s t h at m ay st ick t o t h e u p p er d ies, t h e slid e can
be fit t ed wit h p n eu m at ic, h yd rau lic o r m ech an ical knock-out pins cf.
Fig. 3.2.12 .
3.1.3 Drive systems for deep draw ing presses
Sin gle an d d o u ble-act io n p resses are u sed fo r sh eet m et al fo rm in g. Th e double-action press feat u res, n ext t o t h e d rawin g slid e, also a sep arat e
blan k h o ld er slid e Fig. 3.1.8
, cf. Fig. 4.2.2
. Bo t h slid es are act u at ed fro m abo ve.
Aft er t h e fo rm in g p ro cess, t h e p art m u st , as a ru le, be t u rn ed u p sid e d o wn fo r t h e n ext blan kin g an d fo rm in g o p erat io n . Th is req u ires a
41
Press types and press construction
Fig. 3.1.7 Eight-track slide gib
in cross formation
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
42
Fundamentals of press design
blank holder connecting rod
blank holder slide
blank holder
press bed blank
holder drive
toggle drive
slide connecting rod
draw ing slide draw punch
draw n part female die
foundation press crow n
eight-element slide drive
system
Fig. 3.1.8
Double-action mechanical press
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
43
Press types and press construction
Fig. 3.1.9
Single-action mechanical press w ith draw cushion
draw ing slide
blank holder slide connecting
rod
female die
draw punch draw n part
hydraulic draw cushion
pressure pin press crow n
eight-element slide drive system
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
bu lky, cost-in ten sive tu rn in g d evice to be in stalled d own stream from th e d ou ble-action p ress. Th ere are ad van tages in form in g a p art in th e reverse
p osition , i. e. th e bottom of th e p art facin g u p ward s. In th is case p art ejec- tion is sim p ler th rou gh a slid e cu sh ion in su bseq u en t form in g station s.
Th e altern ative is to work with a d raw cu sh ion or n itrogen cylin d ers. Fu rth erm ore, th e cen terin g in su bseq u en t station s is im p roved , sin ce th e
p arts can be p osition ed over th eir en tire in n er sh ap e by th e bottom d ie. In ad d ition , th e sen sitive su rfaces of th e m aterial – for exam p le wh en
workin g with au tom otive bod y p an els – are less likely to su stain d am age d u rin g tran sp ortation in th e p ress an d wh en cen terin g in th e d ie. It is
also p ossible to in stall th e blan kin g p u n ch es at a lower level for su bse- q u en t op eration s if th e p art h as p reviou sly been tu rn ed over.
In t h e case o f single-acting deep drawing presses, in co n t rast , t h e blan k h o ld er fo rce is t ran sm it t ed fro m u n d ern eat h by a d raw cu sh io n
Fig. 3.1.9 an d cf.
Fig. 4.2.3 . Bo t h t h e fo rm in g an d t h e blan k h o ld er
fo rce are ap p lied by t h e slid e, as t h e slid e fo rces t h e d raw cu sh io n d o wn - ward s. Aft er t h e d rawin g, wit h o u t “t u rn in g o ver”, t h e p art is id eally
p o sit io n ed fo r t h e su bseq u en t o p erat io n s. W h en u sed t o get h er wit h a h yd rau lically d riven slid e m o vem en t , t h e
d raw cu sh io n can also be u sed fo r active counter-drawing Fig. 3.1.10
an d cf.
Fig. 4.2.4 . Fro m t h e p o in t o f view o f en ergy savin gs, it is ben eficial
t h at t h e slid e h o ld s t h e blan k wh ile t h e d raw cu sh io n ap p lies t h e fo rm - in g fo rce.
In o rd er t o ach ieve as great a d egree o f flexibilit y as p o ssible, d o u ble- act io n p resses can also be co n figu red wit h a d raw cu sh io n .
3.1.4 Draw cushions
