Material Formability and Coil Design in Electromagnetic Forming

Pulsed electromagnetic forming is based on high-voltage discharge of capacitors through a coil. An intense transient magnetic field is generated in the coil and through interaction with the metal work-piece; pressure in the form of a magnetic pulse is built up to do the work. Data on formability of two aluminum alloys employed for exterior (6111-T4) and interior (5754) automotive body panels will be shown. Comparison of traditional Forming Limit Diagrams obtained by stretching of aluminum sheet with hemispherical punch to the results on formability, where hemispherical punch is replaced by a coil will be provided. It will be shown that material formability in high-rate forming conditions can significantly depend upon interaction with the forming die: electromagnetic forming into an open round window provides only slight improvement in formability, while forming in a V-shape die or into a conical die indicates a significant improvement. An important part of the electromagnetic forming technology is the design of the coil. The coil failure modes and measures preventing them are discussed.