Research on swinging unit multi-point die with discrete elastic cushion in flexible stretch forming process

Multi-point flexible stretch forming (MPFSF) is a sheet metal forming technology with highly flexible characteristics based on the die and the clamping method. The multi-point die (MPD) surface is composed of many discrete fixed units in MPFSF, and the dimple and stretching ditch will be generated on the formed part surface. Swinging unit multi-point die with discrete elastic cushion can suppress the dimple and stretching ditch, reduce working intensity of elastic cushion removal as well as simplify the process. Two MPFSF finite element numerical models are established for fixed unit with integral elastic cushion (FUIEC) and swinging unit with discrete elastic cushion (SUDEC), respectively. Through detailed numerical simulations and conducting the flexible stretch forming experiments, the results are compared between the two parts formed by FUIEC and SUDEC. According to the results, it is demonstrated that the stress, strain, and thickness distributions are more uniform when forming by SUDEC. Moreover, the stress, strain, and thickness thinning rate values are smaller. In addition, the surface forming quality is improved and the shape accuracy is higher by SUDEC. Therefore, SUDEC can replace FUIEC in a certain extent, and the production efficiency is increased accordingly.