Development of Multilayered Uniform Pressure Tooling Coils for Electromagnetic Pulse Forming

Pulsed power is fundamental to electromagnetic forming methods, which are high-strain rate non-conventional manufacturing processes used for shaping sheet metal, tubes, joining, and explosive welding. Conventionally, thick machined coils (single turn or coils with very thick conductors) are used for forming applications due to their higher mechanical strength. Nevertheless, these coils exhibit low inductance, resulting in exceedingly high peak currents and discharge frequencies. This causes excessive stress in the coil, poor forming efficiency, and increases the cost of switching devices due to current requirements. Wire-wound multiturn coils are also used for forming applications, improving the forming efficiency compared with single-turn coils, but geometrical constraints also limit its design. In this manuscript, the authors have studied the design of multiturn and multilayer coils for electromagnetic forming. The authors have used a uniform pressure tooling coil (UPTC) system and conducted free bulging studies on AA-6061-T6 aluminum sheets to validate the results. The focus of this manuscript is on electromagnetic principles critical in designing multilayered tooling coils. In the electromagnetic formulation, the authors have used an analytical model using current filament methods to calculate the tooling coil parameters and magnetic pressure on the workpiece. In addition, the skin depth of the material is a critical parameter that affects the forming efficiency of the forming system. The authors have also studied the effect of the coil design on the forming efficiency with multilayered coils.