– d evelo p m en t o f a co h esive p ressu re an d t em p erat u re-resist an t lu bri- cat io n film , wh ich sep arat es t h e su rfaces o f t h e wo rkp iece an d t h e
d ie, – h igh ad h esive an d sh earin g st ren gt h as well as go o d wet t in g cap abil-
it y, – n o in vo lu n t ary p h ysical o r ch em ical react io n s o n t h e su rface o f t h e
frict io n al p art n ers, – easy an d co m p let e rem o val o f t h e lu brican t fro m t h e fin ish ed p art ,
– n o u n h ealt h y o r en viro n m en t ally h arm fu l su bst an ces.
4.2.4 Hydro-mechanical deep draw ing
Hyd ro -m ech an ical d eep d rawin g in vo lves t h e u se o f a p ressu re m ed i- u m , gen erally o il wat er em u lsio n , t o p erfo rm t h e fo rm in g p ro cess cf.
Fig. 2.1.13 . Hyd ro -m ech an ical d eep d rawin g is carried o u t u sin g d o u -
ble-act io n h yd rau lic p resses. In ad d it io n , a bed cu sh io n is u t ilised fo r h yd ro -m ech an ical reverse d rawin g.
Die layout Th e lo wer d ie is a so -called p ressu re m ed iu m reservo ir o r wat er co n -
t ain er. It is d esign ed as a p ressu re ch am ber an d serves as a h o ld er fo r t h e p art -sp ecific fem ale d ie
Fig. 4.2.9 . Th e wat er co n t ain er is co n n ect ed t o
t h e p ressu re regu lat o r in t h e p ress. In o rd er t o fast en t h e fem ale d ie o n t h e wat er co n t ain er a clam p o r a sh rin k rin g is u sed . Th is rin g h as
gro o ves, wh ich carry away em ergin g leakage flu id t h ro u gh t h e o ver- flo w. Th e fem ale d ie h as a circu lar gro o ve at t h e ed ge o f t h e d rawin g
rad iu s in o rd er t o lo cat e a st rin g like p o lyu ret h an e seal. Th is is o ver- lap p ed at bo t h ed ges by an an gle o f ap p ro x. 45° wh en in sert ed in t h e
sealin g gro o ve. Th is sealin g gro o ve can be elim in at ed in t h e case o f ro t at io n ally-sym m et rical h o llo w co m p o n en t s, p ro vid ed t h at t h e fem ale
d ie is d esign ed acco rd in gly. Th e u p p er p art o f t h e d ie co n sist s o f t h e blan k h o ld er an d t h e d raw
p u n ch . Th e blan k h o ld er is n o rm ally a cast in g in t o wh ich t h e p art - sp ecific blan k h o ld er in sert is at t ach ed . Th is co n t ain s a circu lar sp lash
rin g d esign ed t o co n t ain leakin g flu id . Th is p o rt io n o f t h e d ie serves also t o brid ge a larger blan k h o ld er o p en in g in t h e p ress. Th e d raw
p u n ch is lo cat ed in sid e t h e blan k h o ld er. Th is is, in gen eral, p ro vid ed
185
Deep draw ing and stretch draw ing
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
wit h an ext en sio n p iece. Th e p u n ch ext en sio n is gu id ed in t h e blan k h o ld er. In p ro d u ct io n d ies, an in t ern al m ech an ical st o p sh o u ld be p ro -
vid ed t o lim it t h e d raw d ep t h . Functional sequence
Th e p ress is o p en ed an d t h e wat er co n t ain er is filled in t h e h o m e p o si- t io n
Fig. 4.2.9 . Aft er t h e in sert io n o f t h e blan k, t h e p ress clo ses an d t h e
blan k h o ld er grip s t h e blan k. Th e blan k h o ld er p ressu re, set at t h e p ress,
186
Sheet metal forming and blanking
Fig. 4.2.9
Layout and function of a hydro-mechanical deep draw ing die 1
2 3
4 slide
blank holder slide
draw punch blank holder
splash ring pressure medium
pressure medium tank
female die shrink collar
press bed pressure control device
seal overflow
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
seals t h e p ressu re ch am ber an d t h e act u al fo rm in g p ro cess is in it iat ed . Th e m ed iu m p ressu re bu ild s u p as a resu lt o f p en et rat io n o f t h e d raw
p u n ch in t o t h e wat er co n t ain er. Du rin g d efo rm at io n , t h e sh eet m et al is p ressed again st t h e d raw p u n ch . Du rin g t h e fo rm in g p h ase, t h e co n t ro l
syst em wh ich is lin ked t o t h e p ressu re ch am ber co n t ro ls t h e ap p licat io n o f t h e h yd rau lic p ressu re in fu n ct io n o f t h e d raw d ep t h .
Aft er reach in g t h e m ech an ically lim it ed d raw d ep t h , t h e p ressu re in t h e ch am ber is released an d t h e p ress t ravels back t o it s h o m e p o sit io n .
Special features of the Hydro-Mec form ing process Th e reaction p ressu re activated with in th e water con tain er by th e p en e-
tration of th e d raw p u n ch h as a m u lti-lateral effect d u rin g th e form in g p rocess an d forces th e m etal to be sh ap ed again st th e p u n ch
Fig. 4.2.10 .
Th e d ry friction between th e p u n ch an d th e sh eet m etal is th ereby su b- stan tially in creased . As a resu lt, th e d rawin g forces in crease to levels con -
sid erably h igh er th an th ose reach ed in con ven tion al d eep d rawin g. At th e sam e tim e, th e p ressu re of th e flu id in th e exp osed p art of th e blan k
between th e fem ale d ie an d th e p u n ch cau ses th e m aterial to bu lge u p ward s. Th is d eform ation creates rad ial ten sile stresses an d tan gen tial
com p ressive stresses.
187
Deep draw ing and stretch draw ing
s w
R b = R+2 mm
s: sheet metal thickness, w : w ater gap, R: draw ing radius, b: w eb w idth at least 7 mm
Fig. 4.2.10 Formation of the draw ing gap during
hydro-mechanical deep draw ing
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Hyd ro -m ech an ical d eep d rawin g allo ws t o ach ieve a sign ifican t ly larger d raw rat io t h an t h at ach ievable in co n ven t io n al d rawin g o p era-
t io n s. W h ilst t h e lim it in g d rawin g rat io u sin g co n ven t io n al t ech n o lo gy is b 2.0, d eep d rawin g ratio lim its of u p to 2.7 can be ach ieved in
h yd ro -m ech an ical d eep d rawin g. Sin ce n o in t erm ed iat e d rawin g an d an n ealin g o p erat io n s are req u ired , very co st -effect ive fo rm in g is p o ssi-
ble. Th e t o o l co st s can also be red u ced becau se o f t h e red u ct io n in t h e n u m ber o f n ecessary fo rm in g o p erat io n s. An o t h er n o t able ben efit is t h e
q u alit y o f t h e su rfaces o f t h e d rawn p art s, as t h e sh eet m et al h as n o t been d rawn o ver a rigid d rawin g ed ge bu t o ver a flu id bead . Co st s fo r
fin ish p ro cessin g o p erat io n s su ch as p o lish in g o r grin d in g are su bst an - t ially red u ced o r o ft en co m p let ely elim in at ed .
Du e t o t h e p ressin g o f t h e blan k again st t h e p u n ch wh ich red u ces t h e am o u n t o f sp rin g back, d im en sio n ally accu rat e p art p ro d u ct io n is p o s-
sible. Th is is p art icu larly im p o rt an t in reflect o r p ro d u ct io n , as n o t o n ly m easu rem en t t o leran ces bu t also o p t ical q u alit ies are t est ed . Th e t h ick-
n ess of th e sh eet m etal for h yd ro-m ech an ically d eep d rawn p arts rem ain s con sisten t with in n arrow lim its. Th is ap p lies p articu larly to th e sm all
red u ction in th ickn ess on th e base rad ii, so th at th in n er blan k can fre- q u en tly be u sed for form in g th e d esired p art.
Press fo rce is h igh er in h yd ro -m ech an ical d rawin g t h an in o t h er fo rm in g m et h o d s u sin g rigid t o o ls, d u e t o t h e react io n p ressu re in t h e
wat er co n t ain er. Here, t h e slid e fo rce F
St
[kN] is t h e su m o f t h e co n ven - t io n al fo rm in g fo rce F
U
[kN] an d t h e react io n fo rce F
Re
[kN], wh ich act s o n t h e p u n ch su rface t h ro u gh t h e p ressu re m ed iu m
Fig. 4.2.11 .
Dep en d in g u p o n t h e p art icu lar blan k m at erials bein g p ro cessed , t h e fo llo win g p ressu res o ccu r in t h e wat er co n t ain er:
– alu m in iu m : 50 – 200 bar – st eel: 200 – 600 bar
– st ain less st eel: 300 – 1,000 bar
4.2.5 Active hydro-mechanical draw ing
