Forming evaluation of complex tube hydroformed components

Currently, the main feedstock of tubular blank material for tube hydroformi ng is derived from slit steel coil, which has been roll formed and electric resistance welded (ERW). From ERW tubular blank, a number of intermediate processing stages such as prebending and preforming may be necessary to ach ieve the final formed component. The end result is a component that may hav e experienced a complex strain path history. The traditional forming limit (strain) curve (FLC) is inherently affected by non-linear strain paths; hen ce, a suitable alternative forming limit criterion has been studied and is proposed for complex tube hydroforming processes. The criterion proposed is the forming limit stress curve (FLSC), which is theoretically independent of strain path and prestrain history. The methods used to generate the FLC and FLSC for tubular blanks are described, and prebending is used as an exa mple to demonstrate how complex tubular component forming operations, and s ubsequent formability, may be evaluated through use of the FLSC. (C) 2000 I oM Communications Ltd.