Effect of the sheet thickness and current damping exponent on the optimum current frequency in electromagnetic forming

Abstract

Current frequency is one of the key effect factors on forming efficiency during electromagnetic forming (EMF) process. In the past, many scholars considered that the optimum current frequency corresponds to the skin depth which should be less than workpiece thickness. This is because the magnetic field will greatly lose if the skin depth is larger than workpiece thickness. In this paper, the 2D sequence simulation method is utilized to predict the electromagnetic sheet bulging, and the simulation results are both in agreement with experimental results. It can be found that the larger of the magnetic field losses, the bigger displacement can be obtained in experiments. This is in stark contrast to previous results reported in literature. We also found that the sheet thickness and current damping exponent both have great effects on optimum current frequency if the discharging energy keeps constant, which can cause the skin depth corresponding to the optimum current frequency to be larger than the sheet thickness. Thus, the current frequency is a very complex factor on electromagnetic forming, and it is difficult to choose the optimum current frequency.