3 Fundamentals of press design
3.7 Casting components for presses
Th e p rop ortion of cast com p on en ts in p resses in term s of th eir weigh t d iffers con sid erably. In in d ivid u al p resses su ch as m in tin g an d coin in g
p resses cf . Sect. 6.8.7
or au tom atic n otch in g m ach in es cf. Sect. 4.6.4
, som e 80 of th e total p ress weigh t is m ad e u p of gray cast iron , in gen -
eral in n od u lar cast iron . Th is p rop ortion is m ad e u p p red om in an tly of large com p on en ts su ch as u p righ ts, p ress fram es an d p ress bod ies
cf. Fig. 3.1.1
. In th e case of large p resses with in d ivid u al p art weigh ts exceed in g 20 t, h owever, weld ed con stru ction s p red om in ate. Freed om
from scale, good m ach in in g p rop erties, n on -leakage of oil an d ad h er- en ce to m ech an ical valu es laid d own in th e d rawin g sp ecification s are
criteria wh ich govern th e q u ality of castin gs. Th ey d eterm in e th e com - p lian ce of castin gs with gen eral m ech an ical en gin eerin g req u irem en ts.
Du e to th e size of th e castin gs an d th eir low p rod u ction volu m e, th ese p arts are typ ically m ad e u sin g th e m an u al m old in g tech n iq u e, i. e. with -
ou t th e u se of m ech an ical aid s. Th e cast in g in d u st ry is ch allen ged t o a far great er d egree by t h e p ro -
d u ct io n o f co m p o n en t s t o d rive m ech an ical p resses, in p art icu lar t ran s- fer p resses. Eccen t ric wh eels, fo r exam p le, cam wh eels, red u cin g gears,
co n n ect in g ro d s an d clu t ch co m p o n en t s rep resen t a p art icu lar ch al- len ge t o t h e cast in gs p ro d u cer d u e t o t h e sp ecial q u alit y req u irem en t s
in vo lved cf. Sect . 3.2.6
. Th e fo cal p o in t o f t h is t yp e o f d rive syst em is t h e eccen t ric wh eel, wh ich can h ave a p art weigh t ran gin g an ywh ere
fro m 5 t o 25 t Fig. 3.7.1
. Fo r t h is t yp e o f co m p o n en t , d u ct ile cast in gs in GGG-70 q u alit y are in creasin gly u sed , wh ile in t h e p ast it was cu s-
t o m ary t o u se st eel cast in gs. Th is ch an ge n ecessit at ed ext en sive exp eri- m en t at io n an d co n t in u o u s fu rt h er d evelo p m en t fro m t h e p o in t o f view
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Fig. 3.7.1
Eccentric w heel of a large-panel transfer press
bo t h o f m et allu rgical an d cast in g t ech n o lo gy. Maxim u m care in t h e p ro d u ct io n p ro cess is an u n d erlyin g req u irem en t . Acco rd in g t o t h e cu r-
ren t st at e o f t h e art in t h e field o f fo u n d ry p ract ice, t h e fo llo win g st rin - gen t req u irem en t crit eria can be co vered wit h GGG-70:
– h igh resist an ce t o wear, i. e. t h e m icro st ru ct u re m u st be p u rely p er- lit ic even wit h wall t h ickn esses o f u p t o 200 m m ,
– gu aran t eed h ard n ess o f 240 t o 300 HB in all wall t h ickn esses – also at t h e t o o t h ro o t ,
– elo n gat io n o ver 2 in o rd er t o avert fract u res an d t o in crease resis- t an ce t o o verlo ad in g.
In it s raw cast st at e, i. e. wit h o u t t ran sfo rm at io n an n ealin g, t h ese m ech an ical req u irem en t s are ach ieved u sin g a select ive allo yin g t ech -
n iq u e. Th e ap p lication of coolin g elem en ts m ad e of iron , steel an d sili- con carbid e, eith er cooled or u n cooled , also serves to en h an ce h ard n ess.
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Casting components for presses
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
However, th e castin g tech n ician can on ly alloy an d cool with in restrict- ed lim its, as elon gation d rop s with in creasin g h ard n ess. Du e to th is typ e
of m etallu rgical-tech n ological op eration , an d becau se of th eir geom etri- cal sh ap e, castin gs su ch as eccen tric wh eels are in evitably exp osed to
h igh d egrees of resid u al stress. As a resu lt, stress relief an n ealin g at 560 to 580 °C is an absolu te n ecessity.
In th e fou n d ry, q u ality stan d ard s m u st be assu red in ord er to avert th e risk of cracks an d fractu res in th e castin gs. Th e m arked ten d en cy of th e
m aterial to form scale su bstan tially im p ed es th e p rod u ction of com p o- n en ts m ad e of GGG-70. Th e p orosity risk th erefore is ad d ressed by feed -
in g an d selective solid ification . All com p on en ts, n atu rally in clu d in g also large p arts for p ress d rive system s, are su bject to h igh ly strin gen t q u ality
con trols, in clu d in g u ltrasou n d , X-ray, crack d etection an d h ard n ess test- in g, as well as testin g of m ech an ical valu es u sin g test-bar sp ecim en , cast
togeth er with p rod u ced com p on en t.
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Fundamentals of press design
Bibliography
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presses, American National Standards Institute Inc., New York 1971. Becker, U., Ostermann, H.-J.: Wegw eiser M aschinenrichtlinie, Bundesanzeiger-Verlag, Cologne 1995.
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Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
4 Sheet metal forming and blanking
4.1 Principles of die manufacture 4.1.1 Classification of dies
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