Analysis of tube hydroforming in a square cross-sectional die

A mathematical model considering sliding friction between the tube and die is proposed to explore the plastic deformation behavior of the tubes during a hydraulic expansion process in a square cross-sectional die. This model is used to predict the forming pressure needed to hydroform a circular tube into a square cross-section and the thickness distribution of the product. FE simulations on tube expansion have also been carried out to compare the analytical results with those by the proposed mathematical model. The effects of the friction coefficient between the die and tube, upon the forming pressures needed and thickness distributions after the expansion process are discussed. Experiments of tube expansion in a square die using a self-designed apparatus are also conducted. The analytical results of forming pressure and thickness distributions of the formed parts are compared with the experimental measurements to verify the validity of this newly proposed model.