Comparison between the effects of PVC mandrel and mandrel-cores die on the forming quality of bending rectangular H96 tube

A new type of mandrel, which is PVC material and supposed as elastic–plastic deformable part in the simulation, is proposed to use in rotary-draw bending process, due to it can fill the tube entirely. The effect of PVC mandrel on the forming quality of rectangular H96 tube, such as tube damage distribution, wall thickness variation, section deformation, springback, is researched by comparing with the traditional mandrel-cores die. It is found that, the maximum damage value obtained with PVC mandrel is smaller than that with mandrel-cores die. The PVC mandrel leads to a smaller tube thickness variation and a more uniform tube thickness distribution compared with the mandrel-cores, for the PVC mandrel brings about smaller stress in the bending process. The PVC mandrel is recommended to be used in the rotary-draw bending process due to its advantage in the prevention of height deformation, though, the constraint effect on the tube width provided by the PVC mandrel is a little weaker than that by mandrel-cores die. Especially, the PVC mandrel with 1.5 times plastic hardening performs excellent well on the reduction of sectional height deformation of symmetrical line. The springback angle obtained with mandrel-cores die is smaller due to the retracting mandrel process. The PVC mandrel should be taken away from the tube before the springback occurs, which can be realized by heating the mandrel to soft.