Study on formability of tube hydroforming through elliptical die inserts

This paper proposes a novel experimental approach to evaluate the formability for tube hydroforming under biaxial stretching through elliptical bulging. The idea comes from the hydraulic stretch-drawing tests with elliptical dies for the right hand side of forming limit curve (FLC). Based on the deformation theory and the classical Hosford yield criterion, an analytical model is constructed for the elliptical bulging of tube hydroforming. Then the novel experimental device is designed with five upper elliptical die inserts and one lower die insert used to produce ellipsoidal bulged domes and some experiments are performed. The linear strain paths in different strain states are verified and the right hand side of FLC for roll-formed QSTE340 seamed tube is determined through the proposed experimental approaches. Finally, a comparison between the theoretical results and experimental data is performed. The theoretical predictions show good agreement with the experimental results.