Analysis of a bulging-pressing compound-forming process for the sheet metal part with a small round corner feature

This study presented a new bulging-pressing compound-forming process to solve the manufacturing problem of a thinwall specimen with a small round corner radius. Its key process parameters were the pre-forming depth, pre-forming concave round corner, and matching relation between the liquid bulging pressure and the backpressure punch velocity in the final forming process. The pre-forming depth determines the material reserves of the small round corner area in final forming. The best pre-forming concave round corner is the minimum punch corner in hydro-mechanical deep drawing. The calculating methods for the pre-forming depth and the pre-forming concave round corner were provided by a theoretical analysis. The mechanical model of the bulging-pressing compound forming process was built. Moreover, the deformation situation in the round corner area with different matching relations between the liquid bulging pressure and the backpressure punch velocity was provided by the stress state analysis. Meanwhile, the influences of the pre-forming depth and the matching relation between the liquid bulging pressure and the backpressure in final forming on the quality of the part were researched based on the finite element simulations and experiments. The accuracy of the theoretical analysis was verified. In addition, the applicability of the new process was proven.