A study of process variables in the electromagnetic bulging of tubes

Abstract

The electromagnetic free-bulging of tubular work pieces of aluminium alloy samples of different hardness, annealed cartridge brass and commercially pure copper has been investigated. For a given capacitance and workpiece metal, a logarithmic plot of the maximum true hoop strain against the electrical energy discharged per unit tube thickness was found to be linear. These results could be expressed by an equation of identical form to a theoretical relationship, enabling the identification of the electrical and material properties concerned. The strain hardening characteristics of the workpiece material were found to play a vital role. For a given electrical energy per unit workpiece thickness, increase in capacitance yielded an increase in tube deformation, as predicted by theory. Deviations from theory occurred with the hard materials and with annealed copper. The former can be explained in terms of the breakdown of assumptions made in the derivation of the theoretical equation and the necessary corrections have been made. In the case of copper, the deviation was considered to be due to the strain rate sensitivity of the material.