Numerical Simulation and Test of Multi-step Forming for Bending Exhaust Tube Parts of Automobile

In order to solve the forming difficulties of a bending exhaust tube of an automobile, the bending and hydroforming process of 441 stainless steel tube was studied to improve the forming quality and forming efficiency of the exhaust tube. The influence of key parameters on forming quality of exhaust tube parts was deeply discussed by using finite element simulation software. Firstly, the influence of different relative bending radius on tube forming was studied. The results show that the 1.5D bending radius can effectively improve the wall thickness distribution and reduce the defects. On this basis,the influence of the pre-expansion process on the forming quality of the tube fittings was further studied, and it is found that the pre-expansion process can effectively improve the wall thickness distribution, and the pre-expansion pressure of 40 MPa is determined by simulation as the best loading pressure. At this time, the maximum thinning rate of the tube fittings is only 17.18%, and the maximum thickness increase rate is 19.09%. Finally, based on the simulation results, the bending and internal high pressure forming experiments were carried out, respectively, and the bending exhaust tube parts meeting the requirements were successfully prepared, which verified the validity of the simulation results.