Die an gles ran ge between 10 an d 45° an d gen erate tap ers with sh ou l- d ers between
a
= 5 an d 22.5° on th e p ressed p art cf. Fig. 6.1.2
. Th e p u n ch load is of m in or im p ortan ce, an d d ep en d s on th e billet m aterial.
It sh ou ld n ot u p set th e billet p lastically, an d cau se bu cklin g stresses in slen d er billets. Neith er of th ese stress valu es sh ou ld be exceed ed . Th e
p rocess is h igh ly sen sitive to flu ctu ation s in th e stren gth of th e startin g m aterials an d to th e q u ality of lu brication , i. e. p h osp h atin g an d soap in g.
6.5.5 Ironing
Iron in g is a p rocess wh ereby a tu bu lar p art with a bottom e. g. backward extru ded or drawn cu p is drawn to redu ce th e wall th ickn ess cf.
Fig. 6.1.2 . Th is is a p rocess in wh ich th e force is in trodu ced m ain ly
th rou gh th e bottom of th e workp iece an d p artially by th e m an drel fric- tion force. As a resu lt, in addition to com p ressive stress at th e die sh ou lder
in let, ten sile stress also occu rs after exit from th e die in th e wall of th e workp iece drawin g p rocess. Th is is in direct con trast to redu cin g, in
wh ich th e force an d th u s also th e com p ressive stress occu rs in th e work- p iece cross section before th e die sh ou lder in let p ress th rou gh p rocess.
Th e p art sh ap e is gen erated by th e drawin g m an drel an d th e iron in g die rin g. It is also p ossible to arran ge several iron in g rin gs on e after th e oth er.
Th e m axim u m d egree o f t ru e st rain ach ievable wh en iro n in g st eel is aro u n d
w
= 0.5
«
A
= 40 d ep en d in g o n t h e m at erial ch aract erist ics. Fo r d ifficu lt t o fo rm m at erials t h is valu e d ro p s t o
w
= 0.35
«
A
= 30 . Die o p en in g an gles m ay ran ge u p t o aro u n d 45°, wh ich resu lt s in t ap ers
u p t o 22.5° in t h e fin ish ed p art cf. Fig. 6.1.2
Cu st o m ary d ie o p en in g an gles fo r iro n in g ran ge bet ween 5 an d 36°. A m in im u m p u n ch fo rce is
ach ieved at an iro n in g an gle o f aro u n d 12°, wh en t h e p ro babilit y o f wall fract u re is m in im u m . Iro n in g is a p ro cess in wh ich an ext rem ely
go o d su rface q u alit y an d excellen t t o leran ces are ach ieved , an d it is, t h erefo re, u sed freq u en t ly as a sizin g o p erat io n .
6.5.6 Upsetting
Up set t in g is d efin ed as “free fo rm in g”, a p ro cess in wh ich t h e p art h eigh t is red u ced , gen erally bet ween flat p arallel d ie su rfaces u p set t in g
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Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
d ies cf. Fig. 6.1.2
. If u p set t in g is carried o u t in a clo sed d ie wit h o u t flash fo rm at io n , fo r exam p le in o rd er t o p ress cylin d rical o r len s-sh ap ed
p re-fo rm s, t h is is referred t o as sizin g. Free u p set t in g cf.
Fig. 2.2.1 is ch aract erized by t h ree p ro cess lim it s:
Dep en d in g o n t h e m at erial, t h e m axim u m t ru e st rain o f
w
= 1.6 can be ach ieved . Th e u p set t in g rat io h
d h eigh t t o d iam et er o f t h e st art in g
wo rkp iece m ay n o t exceed 2.3 fo r sin gle p ressin g, 4.5 fo r d u al p ressin g an d 8.0 fo r t rip le p ressin g, as o t h erwise bu cklin g m ay o ccu r an d t h e
fiber flo w is in t erru p t ed cf. Fig. 6.2.1
. Th e m axim u m d ie p ressu re is 2,300 N m m
2
. In co n t rast t o u p set t in g in wh ich t h e ext erio r co n t o u r an d d im en -
sio n are free fo rm ed , in sizin g t h e wo rkp iece is fu lly en clo sed t rap p ed d ie. Th e sam e p ro cess lim it in g valu es exist as fo r free u p set t in g.
Ho wever, t h e sam e m agn it u d e o f t h e u p set t in g p u n ch lo ad is reach ed at lo wer levels o f d efo rm at io n , as t h e m at erial lean s again st t h e d ie wall.
6.5.7 Lateral extrusion
