Effect of overhang between die and blank holder on thickness distribution in multi-point forming

This In sheet metal stamping, the use of a blank holder is essential to eliminate wrinkling and improve geometric accuracy. It is necessary to leave a gap between the blank holder and the die to facilitate the flow of material during forming. The size of the gap can significantly affect the evenness of the sheet thickness and amount of wastage material. Previous studies focused on the effect of blank holder force and blank holder type to eliminate defects, improve shape accuracy and reduce thickness variation. However, the effect of the overhang distance between the die and the blank holder on thickness distribution has not been considered. This study investigated the influence of the overhang distance on thickness distribution in a flexible multi-point stamping die. The aim was to determine the appropriate gap to obtain the best thickness uniformity. Finite element analysis was employed to simulate multi-point stamping with a blank holder to produce hemispherical parts with different gap values. For the setup used, the simulation results show that a 10mm gap gave a reasonable thickness distribution over the whole deformed sheet. This has been validated experimentally.