HYDROFORMING SHEET-METAL WITH INTERMITTENT CHANGES IN THE DRAW-IN CONDITION OF THE FLANGE

The hydroforming process is performed with and without the presence of the inward flow of the flange. In single-stage hydroforming, improvem ent in sheet formability is observed when draw-in of the flange is pre sent The formability of the blank material is further examined when th e blank is subjected to two double-stage hydroforming processes of dif ferent deformation paths. in Path A, the first stage, which is the pre straining-stage, involves hydroforming the blank with draw-in permitte d to a polar height before the onset of instability, followed by the s econd stage in which draw-in is prevented Path B involves hydroforming with draw-in prevented as the first deformation stage, followed by hy droforming with claw-in permitted as the second. The good correlation between the theoretical and experimental results suggests that double- stage hydroforming can be modelled as a single-stage process having in termittent changes in the draw-in condition of the flange. The finding s herein would also provide better understanding of bow the formabilit y of the blank material is affected by the level of prestrain in each deformation path.