6 Solid forming Forging
6.4 Formed part and process plan
Before p rod u cin g a p art by form in g, p rocesses cold , warm , h ot, p rocess com bin ation s, p rocessin g step s, p relim in ary treatm en t, p rocess p lan
an d in term ed iate treatm en t stages m u st all be d efin ed . In ad d ition , th e force an d en ergy req u irem en ts, as well as relevan t d ie stress levels h ave
to be com p u ted . On ly on th e basis of th ese calcu lation s it is p ossible to d efin e th e p ress con figu ration con cern in g fu n ction al ch aracteristics
su ch as p ress force, n u m ber of station s, d istan ce between station s, strokin g rate, len gth of slid e stroke an d au tom ation related q u estion s.
In so lid fo rm in g ap p licat io n s, p ro cessin g freq u en t ly t akes p lace at t h e lim it s o f p h ysical feasibilit y fo r eco n o m ical reaso n s. Th is ap p lies fo r
exam p le regard in g t h e lim it s o f m at erial fo rm abilit y crack fo rm at io n , st rain h ard en in g, t h e lo ad cap abilit y o f d ies in t ern al p ressu res o f u p t o
3,000 N m m
2
an d lu bricat io n co o lin g co ld weld in g. Fo r t h is reaso n , t h e eco n o m ical ap p licat io n o f so lid fo rm in g d ep en d s t o a large d egree
o n t h e exp erien ce o f t h e d esign er an d t h e d ie m aker. Wit h an efficien t co m bin at io n o f su it able fin it e elem en t p ro gram s fo r p ro cess sim u lat io n
an d exist in g fact o ry flo o r exp erien ce, in m et al fo rm in g p lan t s a bal- an ced relat io n sh ip can be said t o exist bet ween t h eo ry an d p ract ice.
6.4.1 The formed part
Lot size and m aterials So lid fo rm in g rep resen t s a co m p et it ive su bst it u t e fo r m ach in in g
p ro cesses an d in so m e cases also fo r cast in g p ro cesses cf. Sect s. 2.1.1
an d 6.2.1
. Th e h igh d evelo p m en t co st s an d t h e d egree o f in vest m en t
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
req u ired fo r p resses an d d ies m ean t h at cert ain m in im u m p ro d u ct io n q u an t it ies are n ecessary. O n t h e o t h er h an d , becau se o f in creasin g raw
m at erial an d en ergy co st s, t h e h igh d egree o f m at erial u t ilizat io n p o ssi- ble u sin g so lid fo rm in g is exp an d in g t h e lim it s o f eco n o m ic viabilit y
co n t in u o u sly t o ward s sm aller bat ch sizes. Even fo r co m p lex p art s, t h is t en d en cy m ean s t h at bat ch es as sm all as 10,000 p art s p er year can st ill
be eco n o m ically p ro d u ced . A p recise feasibility stu d y is on ly p ossible by con sid erin g th e in d ivid -
u al p art con cern ed an d by m akin g cost com p arison s with m ach in in g p rocesses. Neverth eless, th e an n u al p rod u ction lot sizes listed in
Table 6.4.1 can be con sid ered as th e m in im u m econ om ically viable batch
sizes with resp ect to p art weigh t. Design rules
W h en d esign in g a fo rm ed p art , t h ere are t wo areas o f co n sid erat io n : a geo m et rical asp ect s o f t h e fin ish ed p art an d b t h e lim it at io n s o f t h e
in d ivid u al p ro cessin g o p erat io n s u t ilized in t h e t o t al p ro cess seq u en ce. O n t h e basis o f t h e fin ish ed assem bly read y p art geo m et ry, first o f all
a co ld o r warm fo rged p art is d evelo p ed , t akin g in t o acco u n t t h e fo l- lo win g geo m et rical asp ect s:
– m ach in in g allo wan ces; – ro t at io n ally sym m et rical geo m et ries are very well, axially sym m et ri-
cal geo m et ries well su it ed fo r co ld an d warm fo rm in g; – wall t h ickn esses can be p ressed n o lo wer t h an 1 m m fo r st eel, n o lo w-
er t h an 0.1 m m fo r alu m in iu m ; – d raft an gles, u sed in h o t fo rgin g, are gen erally n o t req u ired fo r co ld
an d warm fo rged p art s in sid e, o u t sid e; – sm all h o les wit h len gt h t o d iam et er rat io s l d 1.5 can n o t be eco -
n o m ically p ro d u ced ;
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Formed part and process plan
Table 6.4.1: M inimum economical batch sizes for solid forming w hen compared w ith machining
Weight Production quantity per year Cold forming Warm forming
0.10 – 0.25 kg 200,000 300,000 0.25 – 0.75 kg 150,000 200,000
0.75 – 2.50 kg 25,000 100,000
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
– sm all variat io n s in d iam et er o n t h e in sid e an d o u t sid e su rface o f t h e fo rm ed co m p o n en t s sh o u ld be avo id ed ;
– m at erial o verflo w m u st be p ro vid ed fo r, d u e t o flu ct u at io n s in billet weigh t e. g. d u rin g fo rward ro d ext ru sio n in t h e ro d len gt h , d u rin g
backward cu p ext ru sio n in t h e cu p h eigh t ; – t ran sit io n rad ii m u st be co n figu red as large as p o ssible; sh arp ed ges
can o n ly be p ressed by u sin g sp lit d ies; – u n d ercu t s can be p ro d u ced , bu t in crease t o o lin g co st s;
– it is gen erally n o t p o ssible t o p ress p lu n ge cu t s, p arallel key gro o ves, t ran sverse bo res et c.;
– slip -on gearin g can be p rodu ced by p ressin g, h igh -p recision in volu te gearin g ru n n in g gears can be p rodu ced with in creased die an d p rocess
develop m en t effort. Th e p ro cess en gin eerin g fact o rs d ep en d o n t h e ext ru sio n t ech n iq u e,
t h e select ed p ro cessin g st ep s, t h e wo rkp iece m at erial, t h e p erm issible d ie lo ad in g an d t h e resp ect ive t ri-axial st ress st at e. Pro cess en gin eerin g
co n sid erat io n s m ay rest rict t h e ran ge o f p art geo m et ries t h at can be fo rm ed fro m billet cf.
Sect . 6.5 .
Volum e calculation Fo llo win g t ran sfo rm at io n o f t h e en d p ro d u ct assem bly read y p art
geo m et ry in t o a fo rm ed p art geo m et ry, vo lu m e calcu lat io n s are m ad e fo r t h e relevan t geo m et ry. In p ract ice, t h e vo lu m e is calcu lat ed by
d ivid in g t h e o verall p art geo m et ry in t o sim p le vo lu m et ric elem en t s, su ch as cylin d ers, t ru n cat ed co n es o r rin gs, wh o se calcu lat ed in d ivid u al
vo lu m es are ad d ed t o o bt ain t h e t o t al p art vo lu m e. Th e calcu lat io n m u st t ake in t o acco u n t p u n ch in g an d sh earin g scrap wh ich allo ws fo r
m at erial o verflo w d u rin g t h e fo rm in g p ro cess. Exp erien ce h as sh o wn t h at t h e vo lu m e calcu lat io n o f t ran sit io n rad ii can be n eglect ed , as
t h ese vo lu m es p art ially can cel each o t h er o u t . A far m o re sign ifican t in flu en ce is d u e t o vo lu m et ric variat io n s t h at resu lt fro m t h e elast ic
d eflect io n an d exp an sio n o f fo rgin g d ies o r m at erial o verflo w wh ich is d ifficu lt t o calcu lat e. Co m p lex ro t at io n ally sym m et rical 2D geo m et ries
are calcu lat ed easily u sin g CAD an d acco rd in g t o Gu ld in ’s law. Ext rem ely co m p lex 3D geo m et ries are h an d led u sin g t h e vo lu m et ric
calcu lat io n m o d u les o f 3D CAD syst em s.
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Solid forming Forging
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
6.4.2 Process plan
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