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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. [ABSTRACT FROM AUTHOR]

Multi-point stretch forming (MPSF), by replacing the traditional rigid fixed-shape stretching die with the multi-point die (MPD), is an important flexible forming technique in sheet metal forming process. However, the particular dimples will be generated on the formed part surface when forming by MPD. In this paper, we prove that the dimple formation can be suppressed by changing the punch units of MPD arrangement. Therefore, the forming effect can be largely improved. Spherical parts are selected as the study objects. Under the same loading condition, two MPSF finite element numerical models are established for conventional arrangement multi-point die (CAMPD) and staggered arrangement multi-point die (SAMPD), respectively. Through the numerical simulations and the stretch forming experiments, the stress, strain, thickness, springback, and shape accuracy are compared between the two parts formed by CAMPD and SAMPD. The results show that the values of the stress, strain, thickness thinning rate, and springback of the formed part are smaller when forming by SAMPD. Moreover, the distributions of the stress, strain, and thickness are more uniform. Also, the surface forming quality and the shape accuracy are improved. These results provide a valuable guidance during developing the new types of MPD. [ABSTRACT FROM AUTHOR]