Comparison of free and restrained bulge forming by finite element method simulation

Abstract

Most finite element analysis of bulge forming or more specifically bulge testing were done for possible simplest cases. These analyses used pressure as forming load holding the periphery fixed thus involving no contact phenomenon. In real forming cases contact is an essential feature and involves pushing of material into the bulge. Ahmed and Hashmi[4] simulated bulge forming of a circular plate applying pressure on plate surface and inward displacement of the plate periphery in a die configuration. It was observed that the bulge formed by the combined load is higher, has more uniform thickness and has less stress and strain. It is expected that if the bulge is restrained at the polar region rather than allowed to form free, it might result in a bulge with longer cylindrical part which is more desirable from manufacturing point of view. This paper presents the results of simulation of bulge forming by combined load with and without a restraining load and without one. It is found that the bulge formed with a restraining load not only has longer cylindrical part but also has higher bulge height than in that obtained without a restraining load at the polar region. However, the restrained bulge developed more stress and strain but their distribution in the bulge are relatively smoother.