Characteristic evaluation of electromagnetic forming system and its application to deformation prediction in bulge forming

Electromagnetic forming (EMF) is an emerging nonconventional technology that relies on the usage of electromagnetic forces to deform a workpiece at high speed. Recently, studies on the application of EMF have been underway, and evaluating the characteristics of an EMF system, that is, the system circuit parameters (resistance, inductance, and capacitance), is necessary to understand the effect of circuit configuration on the performance and to design the coil. In this study, two practical methods were utilized for evaluating the system circuit parameters of a high-voltage EMF system connected with a flat spiral coil involving wires and connectors: the semi-analytical method and inverse optimization method. The semi-analytical method simply obtains the system circuit parameters by subtracting the coil circuit parameters from the equivalent circuit parameters. The coil circuit parameters are calculated analytically from the coil geometry, while the equivalent circuit parameters are extracted from the measured equivalent electric current profile. In the inverse optimization method, an optimization process is performed to obtain the system circuit parameters that achieve the best match between the predicted and measured equivalent electric current profiles. As examples of EMF application, two types of bulge tests, with circular and elliptical shapes, were performed, and they were successfully predicted by the EMF simulation with the obtained system circuit parameters. As a result, the feasibility of the two utilized methods as practical approaches to understand the effect of circuit configuration on the performance and to design the coil was verified.