Transfer presses for small and medium sized parts

4.4.6 Transfer presses for small and medium sized parts

Mech an ical an d h yd rau lic t ran sfer p resses are u sed fo r t h e m an u fact u re o f read y-t o -assem ble co m p o n en t s fo r t h e au t o m o t ive in d u st ry, it s su p - p liers, t h e elect rical an d h o u seh o ld ap p lian ce sect o rs, an d o t h er bran ch es o f in d u st ry Fig. 4.4.23 . Th ese p resses gu aran t ee h igh o u t p u t rat es becau se all fo rm in g o p erat io n s req u ired t o m an u fact u re a wo rk- p iece are in clu d ed in o n e an d t h e sam e lin e. Fu rt h erm o re, all t h ese o p erat io n s are p erfo rm ed n early sim u lt an eo u sly. A p art is co m p let ed wit h each st ro ke o f t h e slid e, irresp ect ive o f t h e n u m ber o f d ie st at io n s in u se. Tran sfer p resses are eit h er su p p lied fro m st acks o f blan ks fro m t h e blan kin g lin e Fig. 4.4.15 o r t h ey p ro cess st o ck d irect ly o ff t h e co il cf. Fig. 4.3.1 . In t h e fo rm er case, t h e p ress is eq u ip p ed wit h a d est acker; in t h e seco n d it is eq u ip p ed wit h it s o wn co il lin e in clu d in g d eco iler, st raigh t en er an d feed syst em . By lo cat in g t h e sh earin g st at io n fo r blan k- 229 Sheet metal forming lines Fig. 4.4.23 M echanical transfer press for the production of w heel hubs nominal press force: 42,000kN; number of stations: 11; feed pitch: 700 mm; slides: 3; strokes per minute: 10-28 Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 in g ou tsid e of th e p ress u p righ t, it is p ossible to ch oose between lateral or lon gitu d in al m aterial feed to th e p ress. Lateral coil feed offers th e ben - efit th at th e scrap web can be rolled in to a coil again . Th e d rawback h ere is th e greater sp ace req u irem en t of a lateral coil feed system . Gen erally sp eakin g, h owever, th e sp ace req u irem en t of a tran sfer p ress is con sid er- ably less th an th at of a p ress lin e; th e lower sp ace req u irem en t also serves to red u ce an cillary costs. Fo rm in g an d blan kin g o p erat io n s can be eco n o m ically p erfo rm ed bo t h o n m ech an ical an d h yd rau lic t ran sfer p resses: blan kin g, in it ial d raw an d su bseq u en t d rawin g p ro cesses, co n t o u r p ressin g, calibrat io n , flat p ressin g, flan gin g, t rim m in g, h o le p u n ch in g, et c. O n t h e o n e h an d , even p art s wit h ext rem e d raw d ep t h s an d co m p lex o r asym m et rical sh ap es can be m an u fact u red o n t ran sfer p resses wit h o u t an y p ro blem s. Ho rizo n t al wed ge-d riven cu t t in g an d fo rm in g t o o ls are also u sed cf. Fig. 4.1.17 . O n t h e o t h er h an d , d ies can o ft en be sim p lified by m akin g m o st effect ive u se o f t h e exist in g n u m ber o f st at io n s. Th e n u m ber o f d ie st at io n s wit h in t h e d ie set s u sed d o es n o t n ecessarily n eed t o be id en t i- cal. Id le st at io n s can easily be byp assed . Tran sfer p resses wit h a large n u m ber o f d ie st at io n s p erm it t h e p ro d u ct io n o f t wo d ifferen t p art s sim u lt an eo u sly p ro vid ed t h e d ie set s are able t o fo rm t h e p art o n fewer st at io n s. In t h ese cases, t h e blan ks are fed syn ch ro n o u sly t o t wo d iffer- en t p o in t s in t h e p ress. Th e total n om in al force an d en ergy costs of tran sfer p resses are gen er- ally lower th an it is th e case for in d ivid u al in terlin ked p resses. Op eratin g an d m ain ten an ce costs are red u ced to a sin gle u n it, an d favorable con - d ition s are created for red u cin g p rod u ction costs d u e to th e elim in ation of tran sp ort d istan ces an d in term ed iate station s. Mechanical transfer presses Mech an ical t ran sfer p resses are bu ilt wit h t wo , t h ree o r fo u r u p righ t s. Dep en d in g o n t h e ran ge o f p art s t o be m an u fact u red an d t h e n u m ber o f st at io n s, t h e p resses are eq u ip p ed wit h o n e, t wo o r t h ree in d ep en - d en t ly d riven slid es Fig. 4.4.23 . Each slid e is d esign ed in d ivid u ally t o sat isfy t h e req u irem en t s fo r size, n o m in al fo rce an d st ro ke. In p art icu lar fo r larger p resses wit h d ifferen t p ress fo rce req u irem en t s at vario u s fo rm in g st at io n s, t h is t yp e o f m u lt ip le u p righ t co n st ru ct io n o ffers co n sid erable ad van t ages. It is cu st o m ary in t ran sfer p resses t o in t egrat e a d raw cu sh io n in t h e bed cf. Fig. 3.1.11 . A h yd rau lic o verlo ad syst em 230 Sheet metal forming and blanking Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 p ro t ect s again st o verlo ad o r in ext rem e cases again st breakage o f t h e slid e, d ie o r p ress as a resu lt o f excessive fo rces cf. Fig. 3.2.10 . In t h e case o f t ran sfer p resses wit h h igh lo ad s at in d ivid u al st at io n s, a t o t al p ress o verlo ad syst em is also p ro vid ed . To eject p art s t h at m ay st ick t o u p p er d ies, it is p o ssible t o eq u ip each st at io n in d ivid u ally wit h p n eu m at ic, h yd rau lic o r m ech an ical eject o rs cf. Fig. 3.2.12 . Th eir eject io n fo rce can be ad ju st ed by m ean s o f p res- su re red u cin g valves o r p ressu re axes. In co n ju n ct io n wit h m ech an ical h o ld -back d evices, t h e eject o rs can also be u sed fo r t h in -walled p art s. In m ech an ical t ran sfer p resses, p art s are t ran sp o rt ed fro m o n e st at io n t o t h e n ext by a grip p er rail syst em wh o se t wo o r t h ree-d im en sio n al m o vem en t is gen erally co u p led m ech an ically t o t h e slid e m o t io n Fig. 4.4.24 . In two-d im en sion al system s, th e grip p er rails execu te on ly th e op en - in g an d closin g as well as forward an d retu rn feed m ovem en ts. If th e workp ieces h ave to be raised at certain station s of th e form in g seq u en ce, th is is execu ted by sp ecial grip p ers. A th ree-d im en sion al tran sp ort sys- tem is u sed in cases wh ere workp ieces req u ire a lift m otion at m ost sta- 231 Sheet metal forming lines Fig. 4.4.24 Tool area of a transfer press for producing oil filter housings Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 tion s. Th e en tire grip p er rail system is th en eq u ip p ed with a lift stroke. Th is p rin cip le, wh ich is d escribed in Sect. 4.4.7 “tri-axis tran sfer p resses”, is gen erally in th e p rod u ction of larger p an els. All t h ree axes o f t h e grip p er rail d rive syst em s are p o sit ively d riven by d o u ble cam s. Co n figu rat io n o f t h e m o t io n cu rves in acco rd an ce wit h m at h em at ical p rin cip les p reven t s jerky accelerat io n s – in o t h er wo rd s, n o cen t rifu gal effect s are creat ed wh ich wo u ld jeo p ard ize reliable wo rk- p iece t ran sp o rt . Th e d ist an ce bet ween t h e grip p er rails p erp en d icu lar t o t h e d irect io n o f t ran sp o rt can be ad ju st ed in fin it ely o r o n a st ep -by-st ep basis. In t h e case o f p art s wit h sm all d im en sio n s, t h is elim in at es t h e n eed fo r lo n g grip p ers an d co rresp o n d in g m o t io n o f large m asses. Hydraulic transfer presses In t h e case o f h yd rau lic t ran sfer p resses, an elect rically d riven grip p er rail syst em t ran sp o rt s t h e wo rkp ieces fro m t h e d est acker t o t h e st o rage lo cat io n beh in d t h e p ress Fig. 4.4.25 . Th e m an u factu re of p arts u sin g th e cou n ter d rawin g m eth od is gen er- ally u sed on ly in h yd rau lic p resses Fig. 4.4.26 , cf. Fig. 3.1.10 an d 4.2.4 . Th e d rawin g p rocess is p erform ed , gen erally in two stages, by active d raw cu sh ion s in th e p ress bed followed by trim m in g an d flan gin g of th e ed ge. Th e slid e closes an d d isp laces th e blan k h old er wh ile th e two rear d ies form th e ed ge. Th e slid e reach es its bottom d ead cen ter wh en it m akes con tact with m ech an ical stop s. On ly after th is stage is reach ed , th e p arts are d rawn u sin g th e p u n ch es by switch in g over th e d rive p u m p s from slid e to bed cu sh ion op eration . Th e blan ks are h eld at every d ie station u sin g th e p re-selected force level actin g from above. On ce th e form in g op eration h as been com p leted , th e slid e op en s wh ile th e bed cu sh ion s retu rn to th eir startin g p osition s. Th e ad van tage of th is form in g m eth od is th at n o tiltin g m om en t acts on th e slid e d u rin g th e form in g p rocess, as th e two h alves of th e d ie set are restin g on each oth er d u rin g th e en tire d rawin g op eration . Th u s, it is p ossible to ach ieve a h igh stan d ard of p art q u ality an d also a favorable en ergy balan ce cf. Sect. 3.3 . If th e p arts are p rod u ced in th e tran sfer p ress u sin g a sin gle-actin g sys- tem with a d raw cu sh ion , large off-cen ter load s can occu r if d rawin g forces com e in to effect in th e first station s, e. g. in th e fron t-m ost d ies, wh ile th e rear d ie station s h ave n ot yet been su bjected to load in g. Th is situ ation lead s to tiltin g of th e slid e, wh ich can be com p en sated with th e aid of a h yd rau lic system con trollin g th e slid e p arallelity cf. Fig. 3.3.5 . 232 Sheet metal forming and blanking Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Wit h in t h e d ist an ce bet ween t h e d ie cen t ers – wh ich co rresp o n d s at t h e sam e t im e t o t h e t ran sfer st ep – t h e d raw cu sh io n s an d bed eject o rs are lo cat ed u n d ern eat h t h e bo lst er. Each d rawin g d ie set req u ires it s o wn d raw cu sh io n wh o se blan kh o ld in g fo rce can be in d ivid u ally ad ju st ed fo r t h e d rawin g p ro cess, carried o u t at each in d ivid u al st at io n cf. Sect . 3.1.4 . Du rin g t h e u p st ro ke m o t io n o f t h e slid e, t h e bed ejec- t o rs raise t h e wo rkp ieces t o t h e t ran sfer p lan e t o allo w t h e grip p er rails t o en gage t h e p art an d t ran sp o rt it fo rward . Hyd rau lic eject o rs in t h e slid e h elp t o p reven t t h e fo rm ed p art s fro m st ickin g in t h e u p p er d ies. Th e fo rce an d t h e sp eed o f t h ese eject o rs m u st be co n figu red in su ch a way t h at t h e p art s rem ain in a d efin ed p o sit io n o n t h e lo wer d ies cf. Fig. 3.2.12 . O p t io n ally, it is also p o ssible t o eq u ip t h e t o o ls wit h lo w-co st sp rin g lo ad ed slid e eject o rs. Ho wever, in t h is case, t h e eject io n o f t h e p art s is n o t well co n t ro lled . 233 Sheet metal forming lines Fig. 4.4.25 Hydraulic transfer press: nominal press force: 42,000 kN; number of stations: 11; feed pitch: 700 mm; slides: 3; strokes per minute: 10-28 Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998

4.4.7 Large-panel tri-axis transfer presses