Bulging behavior of metallic tubes during the electromagnetic forming process in the presence of a background magnetic field

Abstract

Improving the strength and controllability of the magnetic force that acts on a workpiece is important to enhance the forming ability and outcome during the electromagnetic forming (EMF) process. For this purpose, the present article introduces the concept of a background magnetic field (BMF) to enhance or reverse the forming force and proposes a dual-coil EMF system to generate a BMF for tube forming. Relative to the conventional electromagnetic tube forming system with a single coil, the magnetic force and forming capability can be improved with the aid of a BMF. In addition, a BMF can be used to change the magnetic force direction to induce bulging in small tubes by mounting the two coils outside these tubes. To validate the feasibility of this method and the proposed system, experimental and simulation studies were performed to investigate the bulging behavior of aluminum alloy tubes (AA6061-O). The results show that with a BMF, the deformation depth of the tube can be significantly increased, and the optimal strength of the BMF can be determined. Moreover, a BMF can improve the morphology of the workpieces by enlarging the forming areas and reducing their thickness reduction. Furthermore, tube bulging induced by attractive forces can be realized by using a BMF. The presented method and results are significant for EMF system design and practical applications.