Numerical and experimental approach to reduce bouncing effect in electromagnetic forming process using cushion plate

Electromagnetic forming (EMF) is a high strain rate forming process that uses Lorentz force. In this study, electromagnetic forming with a rectangular block shape in the center of the forming die was examined to determine the possibility and applicability of EMF. However, the high speed of the process in the absence of a medium between the coil and the workpiece results in bouncing of the workpiece, which may result in poor forming. So, in this study, the use of a cushion plate is proposed as a means of reducing the degree of bounce in an EMF process. A 3D electromagnetic numerical model using a spiral forming coil was considered. An RLC circuit, coupled with the spiral coil, was numerically simulated to determine the deformation behavior and design parameters, such as the input current and the magnetic forces. A cushion plate was used between the forming coil and the sheet to be deformed to reduce the extent of bounce. In the numerical simulation, the sheet was found to be well fitted to the objective die with the cushion plate. The simulation results showed that the extent of bounce was drastically reduced because of the velocity direction of the workpiece and the cushion plate. The experiment was performed using 24 kJ to deform Al 1100 with a thickness of 1.27 mm, based on the simulation results. The deformed sheet was well formed, and closely fitted the objective die with a minimum of wrinkling, relative to the results obtained without a cushion plate. As a result, an EMF process with a middle-block die was successfully established both numerically and experimentally to reduce the bouncing.