Large-panel tri-axis transfer presses

4.4.7 Large-panel tri-axis transfer presses

Du rin g th e sixties an d seven ties, d evelop m en ts in th e field of p ress lin e tech n ology led to con tin u ou s p erform an ce im p rovem en t, cu lm in atin g in th e syn ch ron ized p ress lin e with fu lly au tom atic p art tran sp ort cf. Sect. 4.4.5 . As a resu lt of d evelop m en ts in large-p an el tran sfer p resses, it was p ossible to im p rove p rod u ction tim es p er p art an d to fu rth er red u ce cap ital in vestm en t, p rod u ction an d storage costs. In con ju n ction with th e in tegrated grip p er rail tran sfer system , th is p ress con cep t in corp orates all th e p rocessin g stages req u ired in a p ress lin e Fig. 4.4.27 . Large-p an el t ran sfer p resses wit h a d ist an ce bet ween d ie cen t ers o f ap p ro x. 2,200 m m an d d ie wid t h s o f u p t o 3,000 m m can p ro cess large wo rkp ieces m easu rin g u p t o 2,500 3 1,500 m m . Th e fo rm in g st at io n s are m o ved so clo se t o get h er t h at several st at io n s can be acco m m o d at ed u n d er a sin gle slid e. Th is red u ces t h e sp ace req u irem en t by 50 an d 70 . Th e req u ired p o wer is red u ced by 40 t o 50 an d t h e in vest m en t by 20 t o 40 . O t h er ben efit s are gain ed as a resu lt o f red u ced m an - 234 Sheet metal forming and blanking Fig. 4.4.26 Transfer die set for a press w ith active counter draw ing and fixed stops stop first draw second draw edge trimming edge flanging slide e ector draw cushion bolster Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 p o wer req u irem en t , in creased safet y again st accid en t s an d red u ct io n o f n o ise at lo wer co st . In th e in itial layou ts of p ress lin es, th e large-p an el tran sfer p ress was com bin ed with a d ou ble-action d raw p ress cf. Fig. 3.1.8 and Fig. 4.4.28 a , m ean in g th at th e d rawin g tech n iq u e cu stom ary on d ou ble-actin g p ress- es was retain ed . Th e ad d ition ally req u ired tu rn over d evice an d syn - ch ron ization of th e p resses, h owever, red u ced th e ou tp u t to ap p rox. 12 p arts p er m in u te. In ad d ition , d u e to th e u se of th e tu rn over d evice cf. Sect. 3.1.3 , th e tim e req u ired for d ie ch an gin g was con sid erably lon ger. In vestm en t, op eration an d sp ace costs still su bstan tially exceed ed th ose of a sin gle-action large-p an el tran sfer p ress. 235 Sheet metal forming lines Fig. 4.4.27 Large-panel tri-axis transfer press nominal press force: 38,000kN; slides: 3; w ork stations: 6; feed pitch: 2,000 mm; strokes per minute: 8-18 Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th ro u gh t h e u se o f recen t ly d evelo p ed , co n t ro lled d raw cu sh io n s in t h e p ress bed , t o d ay it is p o ssible t o execu t e all t h e n ecessary p ro d u c- t io n st ep s o n a large-p an el t ran sfer p ress cf. Sect . 3.1.4 . As wo rkp iece t ran sp o rt fro m t h e first t o t h e last p ro cessin g st at io n n o w o n ly t akes p lace u sin g a sin gle t ran sfer syst em , h igh er t ran sp o rt sp eed s are p o ssi- ble. Dep en d in g o n t h e t ran sfer st ep , t h ese lin es are cap able o f an o u t p u t o f bet ween 15 an d 25 p art s p er m in u t e. Th is co rresp o n d s t o an in crease in o u t p u t o f so m e 50 o ver an au t o m at ed p ress lin e. 236 Sheet metal forming and blanking Fig. 4.4.28 Large-panel transfer press systems a double-action press combined w ith a transfer press b press w ith three uprights c press w ith four uprights 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 a b c Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Press layout Th e d esign o f a large-p an el t ran sfer p ress d ep en d s o n t h e n u m ber o f st a- t io n s an d t h e d ist ribu t io n o f fo rces. Th e fo u r t o seven d ie set s req u ired fo r t h e p ro d u ct io n o f sh eet m et al p art s are d ist ribu t ed o ver o n e, t wo o r t h ree slid es. Th e t ran sfer st ep d ep en d s o n t h e size o f t h e p art s. Th e slid es are gu id ed in eigh t t racks cf. Fig. 3.1.5 . In t wo - an d t h ree-u p righ t p resses, t wo , t h ree o r six d ie set s are each d ist ribu t ed t o o n e slid e Fig. 4.4.28c . Here, t ilt in g o f t h e slid e can o ccu r as a resu lt o f o ff-cen t er lo ad s, an d m u st be p art ially co m p en sat ed by ap p ro p riat e co u n t erm ea- su res in t h e d ie set . In t h e case o f ext rem ely h igh d rawin g fo rces in t h e first wo rk st at io n , a fo u r-u p righ t p ress wit h a sep arat e slid e fo r t h e first st at io n is reco m m en d ed Fig. 4.4.28c . Mo d ern large-p an el t ran sfer p resses are eq u ip p ed wit h lin k d rive sys- t em s in o rd er t o red u ce t h e clo sin g sp eed o f t h e d ies cf. Fig. 3.2.3 . Th e p ress cro wn is sp lit in t o t wo p art s, t h e p ress bed in t o t wo o r t h ree p art s. Th e p ress bo d y is clam p ed by h yd rau lically p re-t en sio n ed t ie ro d s cf. Fig. 3.1.1 . Autom ation Blan k feed , wo rkp iece t ran sp o rt , d raw cu sh io n co n t ro l, p art rem o val an d in so m e cases also t h e st ackin g o f fin ish ed p art s as well as elect rical co n t ro l o f t h e en t ire t ran sfer p ress are fu lly au t o m at ic Fig. 4.4.11 . W h en ch an gin g from on e stack to th e n ext an d wh en ejectin g dou ble blan ks, con tin u ou s op eration of th e destacker is essen tial. Su p p lem en tary attach m en ts for wash in g an d lu bricatin g th e blan k in th e destacker are also freq u en tly in tegrated. Th e first blan k is sep arated off th e stack by fan - n in g m agn ets an d lifted by su ction u n its. It is th en tran sferred to th e cen - terin g station by m ean s of m agn etic belts an d roller con veyors cf. Sect. 4.4.4 . Th e feeder to th e first station lifts th e blan k from th e cen terin g sta- tion an d tran sfers it to th e first p ress station . Su bseq u en t workp iece tran s- p ort is p erform ed by th e tri-axis grip p er rails. Th e grip p er rails in dex th e workp ieces from on e station to th e n ext Fig. 4.4.29 . Dep en din g on th e blan k geom etry, th e rails are eq u ip p ed with p n eu m atically actu ated active grip p ers or sh ovels wh ich su p p ort th e workp iece du rin g tran sp ort. In order to ach ieve a h igh er ou tp u t, th e grip p er rail m ech an ism is m an u fac- tu red for op tim u m weigh t savin gs as a box-typ e con stru ction u sin g h ol- low p rofiles. Th e en tire tran sfer system is electron ically m on itored to ch eck for p art p resen ce, p osition an d o t h er fu n ct io n s. 237 Sheet metal forming lines Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 If t h ere is an u p righ t lo cat ed aft er a d ie st at io n , t h e grip p ers d ep o sit t h e p art o n an in t erm ed iat e st at io n . Th e t h ree m o vem en t s execu t ed by t h e grip p er rails are p erfo rm ed in t h e lo n git u d in al d irect io n t o t ran s- p o rt t h e p art s fro m o n e st at io n t o t h e n ext , in t h e t ran sverse d irect io n in t h e fo rm o f a clo sin g m o vem en t fo r grip p in g t h e wo rkp ieces an d in t h e vert ical d irect io n t o lift o u t t h e d rawn p art s. Th e p at h co vered by t h e grip p er rails in t h e lo n git u d in al d irect io n is eq u al t o t h e d ist an ce bet ween d ie cen t ers. Th e lo n git u d in al m o vem en t o f t h e grip p er rails is act u at ed d irect ly fro m t h e p ress d rive via in t erm ed iat e gears, cam s an d cam levers. Th e clo sin g bo xes fo r lift in g an d lo werin g, an d fo r o p en in g an d clo sin g t h e grip p er rails, are d riven via cam levers an d t h ru st ro d s. Th u s, p art t ran sfer is m ech an ically syn ch ro n ized wit h t h e p ress d rive syst em an d it is t h erefo re p recisely rep ro d u cible. It is p art icu larly ben e- ficial fo r t h e en t ire t ran sfer d rive syst em t o be lo cat ed abo ve flo o r level, as t h is red u ces d ist an ces an d also ch an ges in t h e d irect io n o f m o t io n s. Lo wer m asses, less st rain an d less p lay are t h e resu lt t h u s p erm it t in g a 238 Sheet metal forming and blanking Fig. 4.4.29 Transportation of parts using mechanically driven gripper rail transfer motion curve shovel part-specific tooling gripper rail intermediate station transfer die Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 h igh er st ro kin g rat e an d reliable p art t ran sp o rt . A sp ecial co m p u t er p ro gram o p t im izes t h e m o t io n cu rve o f t h e t ran sfer m o vem en t s regard - in g m ass an d accelerat io n so t h at t h e sh o rt est p o ssible cycle t im es an d ext rem ely sm o o t h m o vem en t s are en su red fo r all st ro kin g rat es Fig. 4.4.30 . Mo t io n cu rves are est ablish ed fo r each t ran sfer syst em an d t h ey are u sed t o ch eck t h e clearan ce o f t h e grip p er rail syst em relat ive t o t h e d ie m o vem en t . A safet y clearan ce o f at least 20 m m m u st be en su red bet ween t h e t o o l an d t h e cu rve in each case. All elem en t s wh ich m ay im p ed e t h is clearan ce, su ch as cam d rives o r gib elem en t s m u st be t ak- en in t o co n sid erat io n cf. Sect . 4.1.6 . Electrically driven transfer In st ead o f m ech an ical t ran sfer syst em s, elect rically d riven syst em s can also be u sed fo r large-p an el p resses Fig. 4.4.31 . Th e p at h , accelerat io n an d sp eed valu es o f elect rical t ran sfers can be freely p ro gram m ed , wh ich allo ws t h e syst em t o be ad ju st ed t o d ifferen t set s o f d ies. 239 Sheet metal forming lines Fig. 4.4.30 M otion diagram of a tri-axis transfer system slide mo ement part transport by transfer transfer return without part lift gripper rails lower gripper rails open gripper rails close gripper rails stroke [mm] crank angle [ ] 2600 2200 1800 1400 1000 600 200 0 30 60 90 120 150 180 210 240 270 300 330 360 Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Wo rkp iece-sp ecific axis d at a, lift in g st ro kes, clo sin g d ist an ces an d wh ere ap p licable also t ran sfer st ep s are en t ered in t o t h e p ress co n t ro l syst em . Elect rical t ran sfers m ake p art icu lar sen se wh erever ju st -in -t im e p ro d u ct io n o f sm all bat ch sizes is called fo r Fig. 4.4.32 . Here, t h e t ran s- p o rt syst em can be ad ju st ed t o a d ifferen t n u m ber o f st at io n s, in so m e cases d ifferen t d ist an ces bet ween d ie cen t ers an d o t h er p aram et ers by accessin g t h e valu es fo r each p art fro m t h e d at a m em o ry. Ho wever, fo r reaso n s o f safet y, t h is h igh d egree o f flexibilit y m ean s co m p ro m isin g o n cycle sp eed s in co m p ariso n wit h m ech an ically co u p led t ran sfer syst em s. In t h e case o f grip p er rails fo r h igh st ro kin g rat es wit h h igh valu es o f accelerat io n an d sp eed , ext rem ely ligh t co m p o sit e m at erials an d alu - m in iu m allo ys are u sed . 240 Sheet metal forming and blanking Fig. 4.4.31 Layout of an electrical transfer system part-specific tooling press upright transverse drive direction of transport gripper rail moving bolster lift low er drive longitudinal drive Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Draw cushion W h en p rodu cin g car body p arts on large-p an el tran sfer p resses, th e blan k h older fu n ction m u st be p erform ed by th e draw cu sh ion in th e p ress bed in order to p erm it th e p art to be fu rth er p rocessed in th e sam e p osition cf. Fig. 3.1.11 . Provided th e geom etry of th e drawn p art is su itable an d with adeq u ate p re-acceleration of th e draw cu sh ion , good resu lts can be obtain ed u sin g p n eu m atic draw cu sh ion s. However, th e blan k h older force con trol is even m ore favorable wh en u sin g m icrop rocessor-con - trolled h ydrau lic draw cu sh ion s Fig. 4.4.33 an d cf. Fig. 3.1.12 . Even with large drawin g dep th s u p to 250 m m , th e u se of th is typ e of draw cu sh ion p rodu ces workp iece q u ality com p arable to th at ach ieved on dou ble- action p resses. However, th is system n ecessitates adju stin g th e die design to th e p ress cf. Fig. 4.1.16 an d tran sfer system , so th at m argin ally h igh er die costs m u st be taken in to accou n t. Retrofittin g of existin g die sets for u se in th is typ e of large-p an el tran sfer p ress m u st be reviewed in d ivid u - ally in each case as regard s co st s an d feasibilit y. A p art icu larly eco n o m - 241 Sheet metal forming lines Fig. 4.4.32 Electrical transfer in a large-panel tri-axis transfer press Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 ical so lu t io n is t o in t egrat e a large-p an el t ran sfer p ress in t o t h e p ro d u c- t io n p ro cess wh en a m o d el ch an ge is m ad e an d wh en n ew d ie set s h ave t o be m an u fact u red . Die change In large-p an el tran sfer p resses, d ies are also exch an ged u sin g m ovin g bol- sters wh ich m ove au tom atically in an d ou t on th e left an d righ t of th e p ress, in som e cases sim u ltan eou sly cf. Fig. 3.4.4 . Th e d ie ch an ge area is safegu ard ed by ligh t barriers an d p artially m on itored by vid eo cam eras. Th e d ie ch an geo ver seq u en ce is d ep ict ed in a d ie ch an ge d iagram . In it ially, t h e p art -sp ecific co n t o u red n est s o f t h e in t erm ed iat e st at io n s are au t o m at ically t ran sferred t o t h e m o vin g bo lst er. Th e p art o f t h e grip p er rails bet ween t h e u p righ t s t o wh ich t h e p art -sp ecific grip p ers are at t ach ed , m u st be exch an ged as p art o f t h e d ie ch an ge p ro cess. 242 Sheet metal forming and blanking Fig. 4.4.33 Hydraulic four-point draw cushion w ith pressure pins displacement cylinders pressure column pressure pins lifting cylinder lifting bridge die cushion box Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Th ese co m p o n en t s are sep arat ed fro m t h e p art o f t h e rail wh ich rem ain s in t h e p ress by m ean s o f an au t o m at ic co u p lin g d evice, an d d ep o sit ed o n t h e m o vin g bo lst er. Aft er releasin g t h e p o wer co n n ect io n s, t h e m o vin g bo lst er wit h t h e d ie an d p art -sp ecific accesso ries t ravels t o o n e sid e o u t o f t h e p ress, wh ile t h e slid in g bo lst er wit h t h e n ext d ie en t ers fro m t h e o t h er sid e Fig. 4.4.27 . Aft er au t o m at ic co u p lin g o f t h e grip p er rails an d p o wer co n n ect io n s, t h e d ie d at a su ch as p ressu re levels an d p o sit io n s are accessed fro m t h e d at a m em o ry an d au t o m at ically set . W h en t h e m o v- in g bo lst er wit h a n ew d ie set is set u p o u t sid e t h e p ress, all t h e p art -sp e- cific d evices su ch as grip p ers an d co n t o u red n est s are exch an ged an d p rep ared fo r t h e n ext p ro d u ct io n p ro cess. A ch aract erist ic feat u re o f large-p an el t ran sfer p resses is t h eir h igh p ro d u ct ivit y wit h an o u t st an d in g d egree o f flexibilit y m ad e p o ssible by sh o rt set -u p t im es. Th e au t o m at ic d ie ch an ge p ro cess p o ssible in large- p an el t ran sfer p resses can be co m p let ed in less t h an 5 m in . Th u s, a m ajo r p reco n d it io n is sat isfied fo r t h e red u ct io n o f cap it al co st s an d o f t h e n eed fo r in t erm ed iat e st o rage o f fin ish ed p art s bet ween t h e st am p - in g p lan t an d t h e bo d y assem bly p lan t . Th is m ean s t h at , d ep en d in g o n bat ch size, it m ay be p o ssible t o p erfo rm several d ie ch an ges p er p ro - d u ct io n sh ift cf. Sect . 4.9.2. Dep en d in g on th e p ress op eratin g p eriod , on a large-p an el tran sfer p ress between 5 an d 30 d ifferen t d ie sets are u sed with batch sizes of 3,000 to 10,000 p an els. To en su re econ om ic u tilization of th e p ress, p arts with n early id en tical form an d size an d a sim ilar d egree of form in g com - p lexity sh ou ld be grou p ed to create fam ilies of p arts cf. Fig. 4.9.2 an d 4.9.3 .

4.4.8 Crossbar transfer presses