Abstract: Multi-gripper flexible stretch forming(MGFSF) is a new innovation of flexible forming. Spherical part is selected as the research object and finite element models of MGFSF are built. The effects of different transition zones on forming force, strain and thickness distributions, and springback of the formed parts are analyzed comparatively. The effects of strain values and strain distribution conditions on springback are also analyzed. The simulation results reveal that the shorter the transition length is, the smaller the forming force is and the easier for the metal sheet gets shape of the die. Furthermore, the shorter the transition length is, the smaller the strain and the thickness reductions will be, in addition, the higher uniformity of the strain and thickness distributions will be. In particular, the metal sheet can get the desired shape without transition zone with MGFSF, which significantly improves the utilization of materials and saves the manufacturing costs. It is also founded that, improving the uniformity of strain distribution has a more effective reduction in springback compared with increasing the strain values. The experimental validation is conducted on the self-developed MGFSF machine.

Key words: flexible forming;stretch forming;numerical simulation;transition zone;springback