Do u ble p art s can be m o st su ccessfu lly p ro d u ced Fig. 4.4.39
o n eigh t -cylin d er d raw cu sh io n s wit h a sp lit p ressu re p ad . Th is allo ws in d i-
vid u al ad ju st m en t o f fo u r cylin d ers p er p art .
4.4.9 Presses for plastics
Metal com p on en ts are bein g rep laced by p lastics in a n u m ber of ap p lica- tion s, in clu d in g th e au tom otive en gin eerin g in d u stry. Th e m aterials u sed
h ere in clu d e FRTP glass fiber-rein forced th erm op lastics an d SMC sh eet m old in g com p ou n d . Th e m an u factu re of th ese p arts im p oses p articu -
250
Sheet metal forming and blanking
Fig. 4.4.39
Hydraulic draw cushion w ith eight displacement cylinders and a split pressure pad
mo ing boster pin holding plate
external box internal box
connection pressure column
crossbar control cam
pilot cylinder outside cylinder
central cylinder intermediate stop
accelerator piston stroke limitation
pressure pin
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
larly st rin gen t req u irem en t s o n t h e p ressin g p ro cess Fig. 4.4.40
. Th e m ajo r d ifferen ce bet ween p ressin g glass fiber-rein fo rced p last ics an d
sh eet m et al fo rm in g lies in t h e m at erial beh avio r, t h e wall t h ickn ess o f t h e p ro d u ced co m p o n en t s an d t h e fo rm in g sp eed .
In sh eet m et al fo rm in g, t h e t h ickn ess o f t h e p art d ep en d s o n t h e st art in g blan k. Th e m at erial t h ickn ess o f a p last ic p art , in co n t rast , is
d et erm in ed by t h e p arallelism an d t h e cavit y o f t h e t o o l. Fu rt h erm o re, p last ic is in sert ed in t h e p ress in a m alleable co n d it io n . It is sh ap ed ,
wh en u sin g t h e SMC p ro cess, by t h e ap p licat io n o f h eat an d wh en u sin g t h e FRTP p ro cess by t h e d issip at io n o f h eat t o fo rm a st able co m -
251
Sheet metal forming lines
Fig. 4.4.40
Hydraulic plastic press for SM C and FRTP parts nominal press force: 18,000 kN; maximum stroke: 1,300 mm
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
p o n en t . Th is im p o ses ad d it io n al d em an d s o n t h e fu n ct io n s o f t h e p ress, in p art icu lar o n t h e sp eed o f t h e slid e. Th is calls fo r t h e u se o f sp ecial
co n t ro l syst em s cf. Sect . 3.3.3
. W h en p ressin g t h erm o p last ics in refrigerat ed d ies, fo rm in g m u st be
p erfo rm ed q u ickly, an d t h e co o lin g p ro cess m u st t ake p lace at a co m - p let e st an d st ill an d wit h o p t im u m p arallelism o f t h e t wo d ie h alves.
In t h e case o f t h erm o set p last ics, a layered m at is in sert ed in t h e d ie. Th e co m p o u n d m at erial – glass fiber an d resin – m u st be p ressed
acco rd in g t o a p recisely sp ecified sp eed p at t ern wit h p recise p arallelism o f t h e t wo d ie h alves, in o rd er t o avo id fiber o rien t at io n . Th e m at erial
h ard en s as h eat is ap p lied . In o rd er t o ach ieve a u n ifo rm p art t h ickn ess, t h e slid e m u st be kep t 0.1 m m m p arallel. Th ese p ro cess p aram et ers
are essen t ial fo r t h e p ro d u ct io n o f h igh -grad e SMC p art s an d can o n ly be im p lem en t ed u sin g a h yd rau lic p ress wit h m u lt ip le axis co n t ro l. Th e
t ech n o lo gical req u irem en t s – fast clo su re, in o rd er t o m in im ize h eat t ran sfer bet ween t h e wo rk-
p iece m at erial an d t h e d ie befo re fo rm in g, – p ressin g at t h e sp ecified sp eed p at t ern t o en su re u n ifo rm fro n t flo w
beh avio r, – p ressin g wit h t h e sp ecified fo rce p at t ern t o en su re ap p licat io n o f t h e
sp ecial p ressu re level req u ired fo r p recise fo rm in g, – h o ld in g t h e p ressu re at a p rescribed level wh ile t h e wo rkp iece h ard -
en s at t h e p recisely p arallel p o sit io n o f t h e t wo d ie h alves, – co n t ro lled o p en in g m o t io n t o avo id d am age t o t h e wo rkp iece
can o n ly be ach ieved u sin g a h yd rau lic p ress. Th e d rive syst em is bu ffered by p ressu re accu m u lat o rs in o rd er t o assu re t h at t h e req u ired
d ifferen t o il vo lu m es are available cf. Table 3.3.1
. Th e slid e o p erat es in a clo sed co n t ro l lo o p , m o n it o red by sen so rs an d co n t ro lled by servo
valves. Th e p arallelism o f t h e slid e is m ain t ain ed wit h in ext rem ely clo se t o leran ces by fo u r cylin d ers act in g o n t h e slid e co rn ers cf.
Fig. 3.3.5 .
4.4.10 Stacking units for finished parts
