Gas Pressure Profile Prediction from Variable Strain Rate Deformation Paths in AA5083 Bulge Forming

Abstract

Two approaches to gas pressure profile prediction for bulge forming of AA5083 sheet under Quick Plastic Forming (QPF) conditions at 450 °C were investigated. The first was based on an algorithm internal to ABAQUS™ wherein the gas pressure results from maintaining a constant effective target strain rate at the dome pole. In the second, the nonlinear long wavelength stability analysis was combined with a single creep mechanism material model that accounts for hardening/softening. A series of stability curves, which denote combinations of strain and strain rate for unmitigated thinning and, ultimately, rupture of an AA5083 bar, were computed. These are based on a parameter that characterizes an assumed geometric non-uniformity, η. The associated uniaxial strains and strain rates were expressed in terms of von Mises effective strains and strains rates, and pressure profiles were computed. An ancillary approach to variable strain rate path prediction based on a thinning factor was used to suggest a suitable value of η in the stability analysis for a reasonable thinning level at the end of forming. Key advantages and disadvantages of both approaches to pressure profile prediction are examined relative to bulge forming time and thinning at a 50-mm dome displacement.