Forming limits for electromagnetically expanded aluminum alloy tubes: Theory and experiment

The electromagnetic forming process is a high-velocity manufacturing technique which uses electromagnetic (Lorentz) body forces to shape sheet metal parts. One of the several advantages of this technique is the considerable ductility increase observed in several metals, with aluminum featuring prominently among these. Motivated by the quasistatic case, recent work has extended the concept of forming limit diagrams (FLDs) to model the ductility of electromagnetically formed sheets. This general theory is hereby applied to study the ductility of freely expanding electromagnetically loaded aluminum tubes. Necking strains are measured in tubes of various geometries which are loaded by different coils and currents. The experimental results are plotted in principal strain space and show reasonable agreement with the corresponding theoretical FLD predictions, which indicate a 2- to 3-fold increase in the forming limits with respect to the quasistatic case.