Effect of die structure parameters on deformation behavior of bent tube in free bending process

The bending section of tube between the bending die and the guider is in a less constrained state during the free bending process. The free bending dies have the important impact on the plastic deformation behavior and the forming quality of tube. To study the evolution law of the deformation behavior of tube with the die structure parameters and optimize the free bending die parameters, the free bending experiments and the corresponding numerical simulations were carried out. The design principle of free bending die was illustrated. The free bending experiment was conducted to verify the reliability of the numerical simulation method. Based on the numerical simulation results, the influence of the distance between the center point of bending die and the front end of guider on the forming quality of bent tube is more obvious than that of the fillet of guider. However, the fillet of bending die hardly affects the stress and strain distribution and the evolution of the wall thickness. Finally, the free bending experiments with the newly determined free bending dies were conducted. The ultimate bending radius of bent tube is reduced and the forming quality is improved.