Rupture instability in hydroforming deep-drawing process

Abstract

The critical fluid-pressure locus above which rupture by tensile instability may occur in the hydroforming deep-drawing process, is formulated and tested. The formulation is based on the classical theory of plasticity (with simple power-law hardening and Mises-Hill normal anisotropic yielding) assuming plane strain tensile failure. Further simplifications, such as assuming constant blank thickness and a constant Coulomb friction coefficient, enable one to account for the coupling effect between the self-adjusted blank curvature and the governing material parameters on rupture. Experiments with copper blanks are aimed to demonstrate that under certain conditions, failure by rupture may be prevented if the path of the working fluid pressure nowhere exceeds the predicted critical-pressure locus path. On the other hand, it is shown that the working fluid pressure should nowhere be lower than a predetermined minimum pressure locus to prevent wrinkles at the rim. Thus a distinct operating zone, lying between the upper and the lower pressure loci, is identified and recommended for practical use.