Investigation of the electromagnetic attractive forming utilizing a dual-coil system for tube bulging

The electromagnetic force between the tube and the coil is generally dominated by repulsive Lorentz force in the existing electromagnetic tube forming systems. In these cases, the coil has to be placed inside the tube for tube bulging, which makes it difficult to achieve when the inner space of the tube is not large enough to accommodate the coil. To solve this problem, a new electromagnetic tube bulging process with an external dual-coil system was developed in this work. According to both numerical and experimental studies, it has been demonstrated that the AA6061-O aluminum alloy tube with a diameter of 33 mm and a thickness of 1 mm can be attracted toward the coil, and the maximum deformation is more than 4 mm after a single discharge. Meanwhile, the tube deformation can be significantly increased by multiple discharges using the attractive forming process. Furthermore, a series of simulations and experiments were carried out to systematically investigate the attractive forming behavior of the tube under different discharge conditions, showing that the discharge voltages of the two coils and the current waveform controlled by a crowbar circuit have a great impact on the tube forming.