Billet or slug preparation

M aterial group Abbreviation No. DIN US designation UNS JIS pure copper E-Cu F20 2.0060 1787 ETP 99,95 C0-0,04O C11000 OFCu SF-Cu 2.0090 1787 DHP Copper C12200 DCu copper alloys CuZn10 2.0230.10 17660 Commercial copper C22000 BS , RBS CuZn28 2.0261.10 17660 Cartridge brass 70 C26000 RBS CuZn40 2.0360 17660 M untz M etal C28000 RBS CuNi2Si 2.0855 17666 Silicon bronze C64700 CN 1 CuNi12Zn24 2.0730.10 17663 65Ni-12Ag C75700 CuNi20Fe 2.0878.10 17664 Cu-20Ni C71000 CuAl11Ni 2.0978 17665 Aluminium bronze C63200 CuSn2 2.1010 17662 Phosphor bronze C50500 als are age-h ard en able th rou gh h eat treatm en t. Th e m ost im p ortan t cop - p er alloys are th e brass fam ily. Th e form ability of th e m aterial im p roves as th e cop p er con ten t in creases an d th e Zn con ten t d ecreases. With a Zn con ten t above 36 , th e m aterials becom e brittle an d th eir cold form a- bility d ecreases rap id ly. As a resu lt, h ot form in g m eth od s sh ou ld p refer- ably be u sed . Flow stress cu rves for cop p er alloys are given in th e VDI Gu id elin es 3134 an d 3200. O t h er m at erials su ch as lead , zin c, t in , t it an iu m o r zirco n iu m an d t h eir allo ys can also be su ccessfu lly fo rm ed . Ho wever, in t erm s o f q u an - t it y an d eco n o m ic sign ifican ce, t h ese p lay o n ly a m in o r ro le.

6.3.2 Billet or slug preparation

Th e wo rkp iece m at erials are sp ecified by t h e u ser: An y m o d ificat io n s t o t h e m at erial, t o exp lo it t h e ben efit s o ffered by co ld fo rm in g h ard en - in g o r t o sim p lify t h e fo rm in g p ro cess, m u st be agreed u p o n wit h t h e d ie m aker an d t h e p ro d u ct io n en gin eer. In ad d it io n t o t h e wo rkp iece m at erial it self, t h e n at u re o f t h e sem i-fin ish ed p ro d u ct , it s sep arat io n t o p rep are in d ivid u al billet s, an d t h e h eat an d su rface t reat m en t are all im p o rt an t p o in t s fo r co n sid erat io n . Sem i-finished products Wires, bars an d t u bes are u sed as sem i-fin ish ed p ro d u ct s fo r t h e p ro - d u ct io n o f billet s o r slu g. Wire is d elivered in co il fo rm an d gen erally 454 Solid forming Forging Table 6.3.3: Selection of copper materials for cold extrusion Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 ran ges from 5 to 40 m m in d iam eter. Wire d iam eters of u p to 50 m m are p rocessed in in d ivid u al cases, alth ou gh th e h an d lin g cap ability of th e wire bu n d le becom es in creasin gly d ifficu lt as th e coils in crease in weigh t. Lo w-co st ro lled wire in acco rd an ce wit h DIN 59 110 an d 59 115 h as a wid e d iam et er t o leran ce an d a ro u gh su rface fin ish . It t h erefo re req u ires p relim in ary d rawin g o n a wire breakd o wn m ach in e. Th e red u ct io n in cro ss sect io n sh o u ld be bet ween 5 an d 8 . Th e wire m u st be an n ealed , d e-scaled an d p h o sp h at ed . Drawn wire aft er DIN 668 K K = co ld d rawn is u sed t o p ro d u ce p art s wit h a lo wer t ru e st rain sm all red u ct io n in area, as t h e m at erial h as alread y u n d ergo n e a cert ain d egree o f p relim in ary st rain h ard en in g d u rin g t h e d rawin g p ro cess. Th is m at erial also h as t o be d escaled , p h o s- p h at ed an d p o ssibly also lu bricat ed st earat e d rawn . W h en a h igh er d egree o f t ru e st rain is in vo lved e. g. cu p backward ext ru sio n , aft er p re- lim in ary d rawin g, an n ealin g G o r sp h ero id ized an n ealin g GKZ m u st be p erfo rm ed in o rd er t o rest o re t h e o rigin al m at erial fo rm abilit y. Th e fo rm o f d elivery is sp ecified wit h t h e d esign at io n s K+G o r K+GKZ. Ligh t o ilin g h elp s p reven t ru st fo rm at io n o n t h e wire. In t h e case o f h igh - allo y st eel q u alit ies, a fu rt h er fin ish d rawin g p ro cess t akes p lace aft er an n ealin g wit h cro ss sect io n red u ct io n s o f less t h an 6 . Th e fo rm o f d elivery is t h en sp ecified as K+G+K o r K+GKZ+K. In p ract ice, bar st o ck can also be u sed eco n o m ically in t h e larger d iam et er ran ges. Wit h d iam et ers o f u p t o 70 m m , bars o f bet ween 6 an d 12 m in len gt h are p ro d u ced . Ho t -ro lled ro u n d st eel t o DIN 1013 an d DIN 59130 is t h e m o st favo rable select io n in t erm s o f co st . Th e allo wable d iam et er t o leran ces can n o t be red u ced by d rawin g, lead in g t o vo lu m e variat io n s. Th ese m u st be fu lly co m p en sat ed fo r by excess m at erial d u rin g t h e fo rm in g p ro cess. Fo r a co m p o n en t weigh in g aro u n d 1.3 kg wit h a d iam et er o f 46 m m , a weigh t t o leran ce o f 88 g average d eviat io n o r 45 g p recisio n d eviat io n m u st be in t egrat ed in t o t h e d ie if t h e ad m issible t o leran ces are fu lly u t ilized . Th e t ran sfo rm a- t io n clearan ce in t h e first st age h as t o t ake acco u n t bo t h , t h e d iam et er t o leran ce an d also t h e o valit y o f t h e billet cau sed by t h e sh earin g p ro cess. Fo r a m at erial wit h a d iam et er o f 46 m m , t h e first t ran sfo rm a- t io n clearan ce will be ap p ro x. 2.5 m m . W h ere ro u n d st eel is bein g co ld fo rged , t h e d escalin g, p h o sp h at izin g an d lu bricat in g o p erat io n s t ake p lace p rio r t o fo rgin g. In t h e case o f warm fo rgin g, t h e billet s are fed d irect ly t o t h e h eat in g lin e. 455 M aterials, billet production and surface treatment Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Diameter Tolerances DIN 668 DIN 59110 59115 DIN 1013 approx. in mm DIN 970 971 DIN 59130 Precision h9 h11 DIN 1013 deviation Usual deviation 15 – 0.04 – 0.10 + – 0.5 + – 0.20 20 – 0.05 – 0.13 + – 0.5 + – 0.20 25 – 0.05 – 0.13 + – 0.6 + – 0.25 30 – 0.05 – 0.13 + – 0.6 + – 0.25 35 – 0.06 – 0.16 + – 0.8 + – 0.30 40 – 0.06 – 0.16 + – 0.8 + – 0.35 45 – 0.06 – 0.16 + – 0.8 + – 0.40 50 – 0.075 – 0.19 + – 1.0 + – 0.50 80 – 0.09 – 0.19 + – 1.3 + – 0.60 Brigh t rou n d steel after DIN 970 an d 971 is d rawn or p eeled followin g h ot rollin g, to toleran ces h 9 h 11. Th e weigh t toleran ce for th e above given exam p le is red u ced to 5 an d 9 g resp ectively, wh ich , in clu d in g an ad m issible len gth toleran ce of 0.2 m m , corresp on d s to th e cu stom ary weigh t toleran ce of between 0.5 an d 1 . By weigh in g th e billets an d ad ju stin g th e cu t-off len gth , it is p ossible to ach ieve weigh t toleran ces of + 1. Peelin g of h ot-rolled bar allows th e elim in ation of su rface in clu - sion s an d seam s as well as an y su rface d ecarbu rization . Table 6.3.4 gives th e d iam eter toleran ces for d ifferen t rou n d m aterials. Alt ern at ively t o bar m at erial, t u bu lar o r rin g-sh ap ed fo rm ed p art s can also be p ro d u ced u sin g t u be sect io n s as billet s o r p refo rm s. Crit eria t o be co n sid ered h ere in clu d e wall t h ickn ess t o leran ce, co n cen t ricit y an d eco n o m y in co m p ariso n t o p ro d u cin g t h ese p refo rm s fro m sh eared bil- let s t h ro u gh u p set t in g, backward cu p ext ru sio n , p iercin g, iro n in g an d by u sin g vario u s in t erm ed iat e h eat t reat m en t s. W h ere h eigh t -t o -d iam et er rat io s are h d 0.2, p ro d u ct io n u sin g sh eared billet s o r blan ks cu t o u t o f h o t -ro lled co il st o ck DIN 1016, flat st eel DIN 1017, t h icker sh eet m et al DIN 1542 1543 is ben eficial. Th is is t h e case p art icu larly wh en irregu lar st art in g sh ap es p refo rm s are req u ired . W h en p ro cessin g wire, it is u sefu l t o h ave t h e p relim in ary t reat m en t p erfo rm ed by t h e sem i-fin ish ed p ro d u ct su p p lier, as a large in vest m en t is req u ired fo r t h is t yp e o f eq u ip m en t an d t h e sp ect ru m o f req u ired t reat m en t t yp es varies great ly. 456 Solid forming Forging Table 6.3.4: Diameter tolerances for round materials w ith selected diameters in mm Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 W h en u sin g bar an d flat m at erial, t h e billet s are gen erally sh eared by t h e fo rger an d su bject ed t o h eat an d su rface t reat m en t . St rain -h ard en - in g effect s wh ich o ccu r p art ially at t h e flat su rfaces o f t h e billet d u e t o t h e sh earin g p ro cess are t h u s elim in at ed p rio r t o fo rgin g. Billet separation Th e m o st co m m o n ly u sed billet sep arat io n p ro cess is sh earin g. Slicin g o n t h e t rim m in g lat h e is u sed o n ly rarely, fo r exam p le fo r t est p u rp o s- es. Blan kin g an d fin e blan kin g are exp lain ed in Sect s. 4.5 an d 4.7 . Sh earin g is ch aract erized by p ract ically lo ss-free sep arat io n at an ext rem ely h igh level o f o u t p u t , in t erm s o f q u an t it y. Th e sh ear blad e p last ically d efo rm s t h e m at erial u n t il it s d efo rm at io n lim it in t h e sh ear- in g zo n e h as been exh au st ed , sh earin g cracks ap p ear an d fract u re o ccu rs. Wit h all fo u r sh earin g p rin cip les – wit h o u t bar an d cu t -o ff h o ld - er, wit h bar h o ld er, wit h bar an d cu t -o ff h o ld er an d wit h axial p ressu re ap p licat io n – p last ic flo w lat eral t o t h e sh earin g d irect io n is in creasin g- ly p reven t ed , wh ile co m p ressive st ress in creases d u rin g t h e sh earin g o p erat io n . Bo t h t en d en cies exercise a p o sit ive in flu en ce o ver t h e geo m - et ry o valit y, t o leran ce o f t h e sh eared su rface. Th e m o st accu rat e billet s are p ro d u ced u sin g t h e sh earin g p rin cip le wit h bar an d cu t -o ff h o ld er. Fo r co ld fo rgin g, t h e sh eared billet s sh o u ld h ave t h e great est p o ssible rect an gu larit y, vo lu m e co n t ro l an d lit t le p last ic d efo rm at io n . Th e sh eared su rfaces sh o u ld be free o f sh earin g d efect s an d exh ibit o n ly a m o d erat e am o u n t o f st rain -h ard en in g. Th e ap p earan ce o f t h e sh eared su rfaces is t h e resu lt o f in t eract io n s bet ween wo rkp iece ch aract erist ics, t o o l, m ach in e an d frict io n . Th e sh earin g clearan ce exercises a m ajo r in flu en ce h ere. Th e great er t h e st ren gt h o f t h e st eel, t h e sm aller is t h e sh earin g clearan ce cf. Fig. 4.5.12 . Ho wever, alu m in iu m an d lead always req u ire a sm all blan kin g clearan ce. Th e fo llo win g valu es m ay be t aken as a gu id elin e fo r t h e sh earin g clearan ce o f st eel: so ft st eel t yp es 5 – 10 o f t h e st art in g m at erial d iam et er in m m h ard st eel t yp es 3 – 5 brit t le st eel t yp es 1 – 3 Ro u gh fract u red su rfaces, t ears an d seam s in d icat e an excessively wid e sh earin g t o o l clearan ce. Cro ss fract u red su rfaces an d m at erial t o n gu es 457 M aterials, billet production and surface treatment Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 in d icat e an in su fficien t t o o l clearan ce. Wit h in creasin g sh earin g velo c- it y, t h e d efo rm at io n zo n e red u ces, t h e h ard n ess d ist ribu t io n beco m es m o re u n ifo rm an d t h e h ard n ess in crease in t h e sh eared su rface beco m es less p ro n o u n ced , i. e. t h e m at erial ch aract erist ics beco m e m o re “brit t le” excep t io n : au st en it ic ch ro m e-n ickel an d ch ro m e-m an gan ese st eels. O p en sh ears an d clo sed sh earin g gu id es are u sed as t o o ls Fig. 6.3.2 . Sh earin g gu id es p ro d u ce very h igh q u alit y blan ks, bu t in vo lve a n u m - ber o f d rawbacks: Sh eared billet s are m o re d ifficu lt t o eject , st o p s h ave t o be u sed an d d em an d s o n t h e d iam et er t o leran ce o f t h e st art in g m at e- rial are m o re st rin gen t . Fo r ro u n d m at erials, t h e relat ive sh earin g clear- an ce fo r each billet t h ickn ess t o be sh eared can be kep t co n st an t by grin d in g an ellip t ical relief cu t o n t h e gu id es. Th e p art s sh eared in t h is way d em o n st rat e im p ro ved an gu larit y an d red u ced bu rr fo rm at io n at t h e ed ge o f t h e fract u red su rface. Mo reo ver, t h e sh eared billet q u alit y is less d ep en d en t o n variat io n s in m at erial p ro p ert ies, wh ich in t u rn red u ces variat io n s in vo lu m e. Th e sh earin g fo rce F S an d sh earin g wo rk W S can be calcu lat ed ap p ro xim at ely wh en sep erat in g ro u n d m at erial wit h t h e d iam et er d u sin g t h e fo llo win g fo rm u la: F S = A S · k S W S = x · F S · s , wh ereby A S is t h e sect io n al su rface t o be sh eared , k S t h e sh earin g resis- t an ce o f t h e billet m at erial an d s ap p ro x. 20 h ard , brit t le m at erials t o 40 so ft , t en acio u s m at erials o f t h e sh earin g st ro ke, i. e. t h e d iam - et er d . Th e co rrect io n fact o r x in d icat es t h e ext en t t o wh ich t h e in crease in fo rce d eviat es fro m a rect an gu lar fo rce-st ro ke cu rve. In gen eral, x is t aken t o be bet ween 0.4 an d 0.7. Th e sh earin g resist an ce k S am o u n t s t o ap p ro xim at ely 0.7 t o 0.8 · R m . Heat treatm ent of steel So ft -an n ealin g sp h ero id ized an n ealin g p lays a p art icu larly im p o rt an t ro le in t h e h eat t reat m en t o f st eel m at erials u sed fo r billet p ro d u ct io n . Recryst allizat io n an n ealin g, n o rm alizat io n an d u n d er cert ain circu m - st an ces also reco very an n ealin g are t yp ical h eat t reat m en t s u sed fo r in t erm ed iat e an n ealin g o f alread y fo rm ed wo rkp ieces wh o se fo rm abili- t y h as been exh au st ed . 458 Solid forming Forging Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th e soft annealing p ro cess sp h ero id izes an y exist in g h ard er flaky ele- m en t s o f t h e m icro st ru ct u re. W h ile t h e h ard n ess is ret ain ed , t h e flo w st ress cf. Sect . 2.2.3 o f t h e m at erial is red u ced . Recrystallization annealing is ad van t ageo u s fo r au st en it ic st eels wit h a lo w carbo n co n t en t , as wit h t h is h eat t reat m en t t h e lo west flo w st ress levels are o bt ain ed . Ho wever, if co arse grain o ccu rs as a resu lt o f lo cally lo w levels o f t ru e st rain o r d efo rm at io n cf. Sect . 2.2.2 d u rin g recryst al- lizat io n an n ealin g, an d if t h is t yp e o f co arse grain is n o t p erm issible, a n o rm alizat io n p ro cess sh o u ld be carried o u t . As a resu lt of two-fold recrystallization p erlite + ferrite = au sten ite an even , fin e-grain ed an d fin e-lam ellar p erlite m icrostru ctu re is ach ieved th rou gh norm alization. Th is can be re-an n ealed if req u ired to create grain ed p erlite soft-an n ealin g. A m arked d ifferen ce in m icrostru ctu re coarse an d fin e grain s can also resu lt d u rin g warm form in g as a resu lt of locally d ifferin g coolin g con d ition s an d d egrees of tru e strain . Th ese d if- feren ces can cau se cracks d u rin g su bseq u en t cold sizin g op eration s red u cin g, iron in g. Th is p roblem can be avoid ed by n orm al an n ealin g. Recovery annealing o ffers a lo w-co st alt ern at ive t o recryst allizat io n o r so ft an n ealin g, p ro vid ed t h e d efo rm at io n in t h e su bseq u en t fo rm in g o p erat io n is m in im al, i. e. t h e level o f t ru e st rain is n o t t o o large.

6.3.3 Surface treatment