Combined electrohydraulic and flexible pin die forming: a novel high strain rate forming die setup

Electrohydraulic forming (EHF) is one of the high-velocity metal forming processes that can significantly increase the formability of metals compared with quasi-static forming processes. On the other way, multi-point forming (MPF) is one of the flexible forming methods that provides different sheet metal geometries by varying the height of the pins. The purpose of this study is to take the advantages of both the EHF and MPF processes by presenting a design for flexible dies to be used in the electrohydraulic forming process. As the first step, electrohydraulic free-forming was performed to investigate the reproducibility and to obtain some of the parameters needed for simulations. Then, the ABAQUS finite element software and Coupled Eulerian-Lagrangian method were used to simulate this process. Afterward, the experimental tests were undergone to determine the defects of the forming process using a flexible pin die. Various geometries were produced by conducting experiments and inserting the proper elastic layer to eliminate the dimpling. The reproducibility and validity of the flexible pin die forming simulation was investigated by analyzing the dome height and final profile of the specimens. After ensuring the accuracy of the simulation, a thicker elastic layer was used to remove the dimpling defect completely. The results of the experiments and simulations illustrated that the use of flexible pin die is possible in the process of EHF and the proper final forms can be obtained by applying the appropriate thickness of the polyurethane layer.