co ld fo rgin g, an d t h e n ecessary su p p o rt in g effect o f t h e su bst rat e m at e- rial is n o t ach ieved . O n ce a co n t in u o u s in crease in t h e h ard n ess o f t h e
su bst rat e m at erial t h ro u gh t o t h e act u al co at in g h as been su ccessfu lly ach ieved , m o re su ccess can be exp ect ed . It m ay be p o ssible t o ach ieve
t h is resu lt u sin g p lasm a n it rid in g an d su bseq u en t co at in g wit h CrN o r TiAlN, o r t h ro u gh t h e d evelo p m en t o f sp ecial san d wich co at in gs.
6.7.4 Die closing systems multiple-action dies
Recen t d evelo p m en t s in t h e field o f d ie clo sin g syst em s h ave su bst an - t ially in creased t h e ran ge o f p art s t h at can be p ro d u ced u sin g t h e co ld
an d warm fo rgin g m et h o d s. Flash less fo rgin g o f sp id ers, sp h erical h u bs, t ie ro d en d s, T-fit t in gs fo r rad iat o r co n st ru ct io n , ro t o rs an d p art s wit h
d ifferen t gearin g h as o n ly beco m e p o ssible wit h t h e d evelo p m en t o f d ie clo sin g syst em s.
Wit h an ad d it io n al clo sin g fo rce in it iat ed in t h e d ie set , fem ale d ies are clo sed befo re t h e bo t t o m d ead cen t er o f t h e slid e is reach ed .
So m ewh at lat er, t h e m at erial is t h en fo rm ed , flash less, in t h e clo sed d ie by p en et rat io n o f t h e p u n ch . Flash less p ressin g is o n ly p o ssible if t h e
p re-fo rm can be co m p let ely lo cat ed in t h e d ies wh en t h ese are clo sed . Th e clo sin g fo rce it self can be in it iat ed by m ean s o f elast o m ers,
h yd rau lic syst em s, o r m ech an ically by t h e kin em at ics o f t h e p ress. Elast o m ers o ffer t h e ad van t age t h at t h eir d esign is sim p le an d t h eir
sp rin g ch aract erist ic can be ad ju st ed wit h in cert ain lim it s by alt erin g t h e m at erial co m p o sit io n . Ho wever, t h ey o n ly p erm it lim it ed t ravel.
Th e elast o m ers also h ave t o be exch an ged p erio d ically. Hyd rau lic clo s- in g syst em s gen erat e h igh clo sin g fo rces wit h in a m in im u m o f sp ace,
an d can t h u s be p o sit io n ed ad jacen t t o each o t h er in m u lt ip le-st at io n d ies. By ad ju st in g t h e p ressu re, a great er clo sin g fo rce ran ge can be co v-
ered . Ho wever, t h eir d esign is m o re co m p lex, an d t h ey call fo r a n u m - ber o f safet y p recau t io n s t o p ro t ect bo t h t h e o p erat o r as well as t h e d ies.
In m o d ern p resses, m ech an ical in it iat io n o f clo sin g m o t io n s can be ach ieved o ver a large cran k an gle ran ge. Ho wever, t h e in vest m en t h ere
is su bst an t ially h igh er t h an t h at n eed ed fo r elast o m er o r h yd rau lic sys- t em s.
Figure 6.7.9 illu st rat es t h e basic layo u t o f a h yd rau lic clo sin g syst em
in t egrat ed fu lly in t o t h e d ie. In t h e p ro vid ed exam p le, t h ere is a clo sin g
502
Solid forming Forging
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
syst em in t egrat ed in t o bo t h t h e u p p er an d t h e lo wer d ie. Th is t yp e is u sed p red o m in at ely in cases wh ere t h ere is o n ly o n e fo rgin g st ep o r
wh en o n ly o n e st at io n o f a m u lt ip le-st at io n d ie is req u ired t o wo rk wit h a clo sin g syst em cf.
Sect . 6.7.1 . Typ ical wo rkp ieces p ro d u ced in t h is
d ie in clu d e gearin g elem en t s wh ich are bein g fo rm ed fro m p re-fo rm ed blan ks rin gs, len ses. Clo sin g syst em s can also be acco m m o d at ed in
sep arat e n eu t ral p lat es Fig. 6.7.10
wh ich always rem ain in t h e p ress irresp ect ive o f t h e act u al d ie in u se. Dep en d in g o n t h e d ie set , m o u n t ed
in t h e p ress, t h e clo sin g syst em s wh ich are cu rren t ly req u ired can be act ivat ed an d co n n ect ed by m ean s o f p ressu re p in s t o t h e fem ale d ie. A
t yp ical ap p licat io n fo r t h is syst em is t h e p ro d u ct io n o f t ie ro d h ead s an d T-fit t in gs wh ich req u ire u p t o five clo sin g syst em s. Ad d it io n al p art s
in clu d e in n er races o f co n st an t velo cit y jo in t s wh ere an ad d it io n al p iercin g p ro cess is req u ired an d t h e gro o ves, fo rm ed in t h e p revio u s st a-
t io n , m u st m ain t ain t h is sh ap e accu rat ely d u rin g t h e p iercin g o p era- t io n .
Th e clo sin g fo rce can be in d ivid u ally ad ju st ed acco rd in g wit h t h e an n u lar p ist o n su rfaces. Th e p ress fo rces wh ich are in t ro d u ced d o wn -
503
Die design
bed bed
clamping plate hydraulic cushion
low er die hydraulic cushion
upper die
annular piston annular piston
cushion pins cushion pins
top advancing die
bottom da
yl ig
ht slide
Fig. 6.7.9 Single-station die set w ith
hydraulic closing system at the top and bottom
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
ward s in t o t h e p ress bed via a co u n t erp u n ch are abso rbed cen t rally. Th is d et erm in es t h e m in im u m in sid e d iam et er o f t h e an n u lar p ist o n .
As a gu id elin e, t h e clo sin g fo rce can be est im at ed t o be 0.6 t o 0.9 t im es t h e p u n ch lo ad . Th e req u ired clo sin g fo rce d ep en d s o n wh et h er a co m -
p let ely clo sed o r t rap p ed d ie set is bein g u sed o r fo rgin g t akes p lace t h ro u gh ext ru sio n sh o u ld ers in t o a free sp ace. In t h e case o f co m p let e-
ly clo sed t rap p ed d ie set s, t h e clo sin g syst em also serves t o ap p ly an axial p re-st ress o n t h e p art in g lin e o f t h e d ies, t h at are su bject ed t o h igh
lo ad s.
504
Solid forming Forging
da yl
ig ht
bed slide
oil cushion annular piston
neutral plate for the closing
system neutral plate
for the closing system
counterpunch cushion pins
Fig. 6.7.10
M ultiple-station die set w ith hydraulic closing systems at the top and bottom of each station
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
6 Solid forming Forging
6.8 Presses used for solid forming 6.8.1 Choice of press
