The effect of coil polarity on electromagnetic forming using a multi-coil system

Abstract

Electromagnetic forming, by combining multiple coils and multiple capacitor banks, is an emerging manufacturing method that can produce flexible spatial-temporal patterns of the Lorentz force to shape metal workpiece. In this process, the polarity of the discharge currents is a key element because it determines the polarity of the magnetic field that is individually induced by each coil, which in turn affects the resulting magnetic field, the Lorentz force, and ultimately the deformation of the workpiece. Aiming to evaluate the potential effects of coil polarity, this paper performed a comparative experimental and numerical study, using a dual-coil system. It is found that the workpiece deformation is sensitive to the coil polarity with respect to both energy efficiency and performance. Furthermore, the analysis of the electromagnetic dynamics shows that the coil polarity would affect the workpiece deformation by altering the electromagnetic interaction between the coils and the workpiece. In this way, both the discharge currents on the coils and the eddy currents on the workpiece would be altered. And consequently, the produced Lorentz forces and thereby the workpiece deformation are affected. The results in this study can be useful for the coil polarity selection that is required in multi-coil forming processes.