d evice wh ich ch ecks p art weigh t . Th e d evices u sed h ere are elect ro n i- cally co n t ro lled au t o m at ic scales, wh ich are m o u n t ed bet ween t h e
lo ad in g syst em an d t h e feed in g st at io n . Part s wh ich are t o o h eavy o r t o o ligh t are au t o m at ically eject ed . Th e weigh in g accu racy is belo w
0.2 o f wo rkp iece weigh t . Th ese d evices are able t o weigh au t o m at i- cally u p t o 80 p art s p er m in u t e.
Die change Fast d ie ch an ge can be a d ecisive factor wh en it com es to th e econ om ic
viability of a p ress, in p articu lar wh en workin g with sm all batch sizes. Both d ie set an d in d ivid u al d ie ch an gin g system s are u sed cf.
Fig. 3.4.5 .
Th e basic d ie ch an ge p rin cip le u sed in p resses for sh eet m etal form in g an d solid form in g are very sim ilar. A m ore d etailed d escrip tion is p ro-
vid ed in Sect. 3.4
. However, d ie ch an ge is on ly on e asp ect wh ich d eter- m in es sh ort set-u p tim es in au tom atic p ress lin es. Fast resettin g of th e
load in g an d feed system s is eq u ally im p ortan t h ere.
6.8.5 Special features of hot and w arm forming lines
Th e sp ecial su p p lem en t ary eq u ip m en t d escribed in Sect . 6.8.4 is also u sed fo r h o t fo rm in g. An ad d it io n al an d essen t ial req u irem en t o f h o t
fo rm in g syst em s is an effect ive co o lin g an d lu bricat io n syst em . Dep en d in g o n t h e d egree o f fo rm in g d ifficu lt y, basically t wo d ifferen t
syst em s are u sed : Flooding
Dies are cooled an d lu bricated by con tin u ou s flood in g u sin g sp ecial lu brican ts, som e of wh ich are m ixed with water at a ratio of between
1 : 2 an d 1 : 4. Th e lu brican t an d water m ixtu re is fed toward s th e d ie th rou gh boreh oles an d sp ray rin gs, an d d rain s away via gen erou sly
d im en sion ed ch an n els. Th e lu brican t is su p p lied from a cen tral reservoir with a cap acity of between 400 an d 1,000 l by m ean s of m ed iu m p res-
su re p u m p s workin g at a p ressu re level of 10 to 20 bar cf. Sect. 3.2.11
. Used lu bricatin g em u lsion is collected , p u rified an d retu rn ed to th e
reservo ir, wh ich is eq u ip p ed wit h a re-co o lin g syst em . Filt ers in t h e ret u rn an d p ressu re circu it s t ake care o f t h e n ecessary p u rificat io n . Th e
lu brican t is m ixed wit h bact ericid es in o rd er t o p reven t bact erial in fes-
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t at io n . As t h is wo u ld ren d er t h e lu brican t u n u sable, bact ericid es are gen erally ad d ed t o t h e lu brican t s by m o st su p p liers. Th e lu brican t
q u an t it ies are set u sin g sim p le m an u al co n t ro l d evices. Au t o m at ic d evices fo r co n t ro llin g t h e lu brican t q u an t it y are available. W h ere
lu brican t s co n t ain grap h it e, an agit at in g d evice in t h e reservo ir is essen - t ial in o rd er t o p reven t so lid grap h it e p art icles fro m set t lin g d o wn in
t h e reservo ir. Spray system s with com pressed air as carrier
Mist coolan t ap p lication system s p rovid e an extrem ely fin e su rface film of coolan t an d lu brican t for op tim u m coolin g an d lu brication . Coolan ts
an d lu brican ts are fed u sin g a join t p ip e. Water is u sed for coolin g, wh ile d ep en d in g on th e p rocess in volved , d ifferen t lu bricatin g agen ts can be
u sed . Grap h ite-free em u lsion s con tain in g water-m ixable oils are gen er- ally u sed for sim p le form in g op eration s. W h ere m ore com p lex form in g
p rocesses h ave to be p erform ed su ch as con stan t velocity join t com p o- n en ts u sed in veh icle d rive system s, em u lsion s m ad e of oil an d grap h ite
are u sed . Th ese em u lsion s com p rise a 1 : 1.3 to 1 : 4 m ixtu re with water. Th e wat er an d lu brican t q u an t it ies are co n t ro lled alt ern at ively by elec-
t ro -valves. Co m p ressed air is u sed as a carrier m ed iu m fo r t h e lu brican t . Co m p ressed air an d wat er o r lu brican t are m ixed t o creat e a m ist in a
m ixin g valve an d fed t o t h e d ie t h ro u gh a jo in t p ip e. Th e elect ro -valves are co n t ro lled in d ivid u ally fo r each st at io n .
Cooling system s for forging Du rin g au t o m at ic fo rgin g, h igh -p ressu re sp ray syst em s 80 –120 bar are
u sed fo r co o lin g p u rp o ses. Th ere is gen erally n o n eed fo r ad d it io n al lu brication . In ord er to ach ieve th e n ecessary d egree of h eat d issip ation ,
con sid erable q u an tities of water are req u ired between 40 an d 60 m
3
h . Th e coolin g water is clean ed , recooled an d th en re-u sed . Th e scale col-
lected in th e water m u st be rem oved u sin g screen s an d filters. Billet heating
Billet s are h eat ed by in d u ct io n . Fo r t h e t em p erat u re ran ge o f 760 t o 800 °C, in d u ctor ou tp u ts of ap p rox. 0.24 kW are req u ired p er kg of steel.
Dep en d in g on th e billet d iam eter, th e freq u en cy ran ge lies between 2 an d 4 kHz. For forgin g tem p eratu res from 950 to 1,100 °C, arou n d 0.40
to 0.45 kW kg of steel are req u ired at freq u en cies of 1 to 2 kHz. In gen -
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Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
eral, alu m in iu m an d alu m in iu m allo ys are also h eat ed by in d u ct io n t o t em p erat u res bet ween 420 an d 480 °C, d ep en d in g o n t h e allo y. Th e
req u ired in d u ct o r o u t p u t is ap p ro x. 0.35 t o 0.4 kW kg wit h a freq u en cy o f 0.5 t o 1 kHz.
Th yrist o r-co n t ro lled syst em s are u sed as co n vert ers. Co n sid erable q u an t it ies o f co o lin g wat er are req u ired t o co o l t h e in d u ct o rs. Reco o l-
in g is p erfo rm ed in t h e p lan t ’s o wn reco o lin g syst em s o r in sep arat e in st allat io n s.
Billet preparation Warm fo rm in g 680 t o 800 °C o f sh aft -sh ap ed p art s m ad e o f st eel fre-
q u en t ly calls fo r co at in g p re-grap h it izin g o f blan ks. Th is m easu re serves t o in crease d ie service life an d is p art icu larly ben eficial fo r first
p ressin g op eration s gen erally forward extru sion or red u cin g op eration s. Th e grap h ite can eith er be tu m bled on p rior to h eatin g, or sp rayed on
d u rin g th e h eatin g p rocess. Th is en tails in d u ctive p re-h eatin g of th e blan ks ap p rox. 180 °C, followed by sp ray ap p lication of th e grap h ite-
water m ixtu re. Th e water evap orates over a relatively sh ort travel, d u rin g tran sp ort to th e m ain in d u ction h eater. Th u s, th e billets are h eated with
a d ried -on coatin g of grap h ite. Alth ou gh a p rop ortion of th e ap p lied grap h it e bu rn s, a relat ively h igh p ercen t age ap p ro x. 60 st ill p erm it s
lu bricat io n an d , t o get h er wit h a very t h in scale layer, creat es t h e d esired lu bricat in g an d sep arat in g effect in t h e d ie.
6.8.6 Sizing and coining presses
