M aterials and heat treatment

5 Hydroforming

5.5 M aterials and preforms for producing hydroformed components

5.5.1 M aterials and heat treatment

Basically th e sam e m aterials wh ich can be u sed for oth er cold form - in g tech n iq u es su ch as d eep -d rawin g cf. Table 4.2.3 are su itable for h yd roform in g ap p lication s. Th e m aterial sh ou ld h ave a fin e-grain ed m icrostru ctu re an d be soft-an n ealed . Th e best fo rm in g resu lt s are ach ieved u sin g m at erials wit h a h igh d egree o f u lt im at e elo n gat io n , wh ereby t h e u lt im at e elo n gat io n at righ t an gles t o t h e lo n git u d in al d irect io n o f t h e t u be – i. e. gen erally at righ t an gles t o t h e ro llin g d irect io n o f t h e sh eet m et al – is im p o rt an t fo r t h e co n figu rat io n o f h yd ro fo rm co m p o n en t s. A h igh d egree o f st rain h ard - en in g is ben eficial. Th e t u be m an u fact u rin g p ro cess an d p re-fo rm in g brin g abo u t a st rain h ard en in g effect wh ich m ay h ave t o be elim in at ed by an n ealin g fo r cert ain co m p o n en t s p rio r t o t h e h yd ro fo rm in g p ro cess. If t h e fo rm a- bilit y o f t h e m at erial is exceed ed d u rin g a p ro d u ct io n st ep in t h e m an - u fact u rin g p ro cess, fo rm in g m u st be p erfo rm ed u sin g several st ages p ro gressive fo rm in g wit h in t erm ed iat e an n ealin g. Ho wever, d u e t o t h e ad d it io n al co st s in vo lved , h eat t reat m en t sh o u ld o n ly be carried o u t wh en all o t h er p o ssibilit ies, fo r exam p le d esign o r m at erial m o d ifi- cat io n s, h ave been exh au st ed . Th e p referable m et h o d o f h eat t reat m en t fo r austenitic st eels is so lu - t io n izin g – id eally u sin g in ert gas. Fo r sm all p art s, a co n t in u o u s fu rn ace can be u sed . Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 In t h e case o f ferritic st eel, t h e t yp e an d p ract icalit y o f h eat t reat m en t d ep en d h eavily o n t h e resp ect ive m at erial an d it s fo rm in g h ist o ry. O n p rin cip le, eit h er o f t wo p o ssible p ro cesses can be u sed : recryst allizat io n an d n o rm al an n ealin g. Gen erally, Mn o r Si allo ys are u sed fo r alum inium . Th e m o st favo rable m et h o d o f h eat t reat m en t m u st be d et erm in ed in each in d ivid u al case, wh ereby p art icu lar at t en t io n m u st be p aid t o t h e lo n g-t erm beh avio r o f t h e m at erial, an d in t h e case o f st rain h ard en in g allo ys, t o rap id fu rt h er p ro cessin g.

5.5.2 Preforms and preparation