Two-step electromagnetic forming process using spiral forming coils to deform sheet metal in a middle-block die

Two-step electromagnetic forming (EMF) of a metal sheet into the shape of a middle block is proposed in this paper. EMF is a high-speed forming process involving the application of a Lorentz force to the workpiece. The high speed of the forming process produces bouncing of the workpiece, which may result in poor shape accuracy owing to the absence of a medium between the coil and the workpiece. The proposed two-step EMF was used to solve this problem. In the demonstration of the proposed method, a 3D numerical simulation of the current supplied through the forming coil was performed using an LS-DYNA electromagnetism module, and the results were used to select a spiral forming coil with a 50-mm dead zone for the first step of deforming the workpiece. The process did not adequately achieve the desired shape, and, based on the results of another simulation, a second forming coil with a 20-mm dead zone was used for the second forming step of completing the fit with the forming die. The experimental results showed that the accuracy in shape achieved by the proposed multistep forming process was better than that of the single-step process, especially regarding the reduced wrinkling and sharpness of the edge of the workpiece.