Simulation of multi-stage tube hydroforming and optimization of forming conditions

Tube hydroforming processes are composed of multiply stages such as bending, springback, pre-forming and hydroforming. To allow designers to carry out the tube hydroforming simulation efficiently and accurately, the new features for tube bending and hydroforming are developed and supplemented to the multi-stage sheet metal forming system JSTAMP-Work. In the system, the commercial FEM codes LS-DYNA, JOH/NIKE are adopted. As the examples, the authors simulated bending, springback, pre-forming and hydroforming processes sequentially using JSTAMP-Works. The effects of previous stages on the results of hydroforming are investigated. According to the results, it is concluded that not only the initial displacement, but also the initial stress, strain, thickness induced in previous stages must be fully considered in the simulation. Furthermore, the authors take internal pressure and axial displacement in hydroforming process as design variables, and then the optimal forming parameters are determined using a general optimization program AMDESS. Based on the numerical results, the formable conditions can be estimated.