Coil Development for Electromagnetic Corner Fill of AA 5754 Sheet

Abstract

Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency magnetic field to form the workpiece into a desired shape. It has been reported by several researchers that EM forming (EMF) increases the formability of hard-to-form aluminum alloy sheet under certain circumstances. EMF can be combined with conventional forming (e.g. stamping) operations to create a hybrid forming operation that exploits the strengths of each process. One such operation is the “corner fill” operation, which consists in pre-forming sheet using conventional forming and then using EMF to reduce the radii of different features on the part to values that could not be obtained with conventional forming. This paper describes the development of a coil used for a hybrid operation that consisted on pre-forming AA 5754 1 mm into a v-shape with a 20 mm outer radius and then reducing or “sharpening” the radius to 5 mm using EMF. The coil is one of the most important components of an EMF operation, since it is the means of delivering the energy to the workpiece. Coils are subjected to very high stresses and are typically the element of an EMF operation that will fail first. One successful and four unsuccessful coils designs are presented. The successful coil was a single loop design, with the section closest to the part narrowed to increase the current density. The simplicity of the shape was chosen for its current flow characteristics and for its structural strength.