Electromagnetic forming of aluminum circular tubes into square tubes: Experiment and numerical simulation

This work discusses dynamic deformation behavior and deformation control during 5A02 aluminum alloy tube expansion into square section ends by electromagnetic forming (EMF) per both numerical simulations and experiments. The results show that as the tube is deformed through single-step EMF, its straight side fails to attach to the die for high-speed impact and rebounding; the corner is thus difficult to fill. Necking and rupture occur in the straight side close to the corner under the combination of the tensile stress caused by the rebound due to the high-speed impact and the inhomogeneous friction along the straight side of the tube. A two-step EMF method is proposed that consists of a uniform circular tube bulging to maximum diameter followed by corner-filling to realize coordinated deformation between the straight side and corner. During the two-step EMF process, necking of the straight side close to corner during singe-step EMF is effectively inhibited and deformation uniformity along the circular direction of the tube is improved. Maximum relative thickness deviation was reduced from 28% to 7% in an experimental validation of the two-step EMF.