Electromagnetic Force and Formability Analysis of Tube Electromagnetic Bulging Based on Double-Layer Concave Magnetic Field Shaper

Electromagnetic forming technology has significant advantages over mechanical processing technology in the processing of light alloy materials and is an important way to realize energy saving and emission reduction in aerospace, automobile manufacturing and other fields. However, the traditional electromagnetic tube expansion process has the defects of serious wall thinning and uneven axial deformation. Based on the traditional electromagnetic tube expansion system, this paper proposed a novel type of double-layer field shaper to regulate the distribution of magnetic field and electromagnetic force. The new field shaper structure can adjust the radial electromagnetic force distribution characteristic from “small at the ends, large in the middle” mode to “large at the ends, small in the middle” mode. And the smaller axial electromagnetic force at the end of the tube can be adjusted to a larger electromagnetic force. The adjustment of the radial electromagnetic force field distribution can weaken the radial electromagnetic force in the middle of the formed tube, thus changing the deformation shape of the tube and improving the characteristics of uneven axial deformation of the tube; the adjustment of the axial electromagnetic force field distribution can promote the flow of the material at the end of the tube to the middle area, compensating for the reduction of the wall thickness of the tube due to radial expansion, thus suppressing the wall thickness thinning phenomenon of the tube. To verify the effectiveness of the double-layer field shaper, the finite element model of electromagnetic coupling structure for the electromagnetic tube expansion system was established by using COMSOL software. In this paper, the change laws of the key physical quantities, such as, the electromagnetic force distribution, the axial deformation uniformity and the wall thickness thinning amount were compared and studied under the condition with or without field shaper. On this basis, the influence of the inner cavity depth of the field shaper on the forming effect of tubes was further explored. The simulation results show that the new field shaper structure improves the axial uniformity by 2.31 times compared with the traditional expansion process, and reduces the wall thickness thinning from 22.07% to 8.30%. The effectiveness of the new field shaper structure in improving the wall thickness thinning and uneven axial deformation of tubes was verified. In addition, increasing the concave height of field shaper is helpful to restrain the wall thinning of tubes, and increase the axial uniformity in a certain range. However, with the further increase of the concave height of field shaper, the radial and axial force fields in the tube forming area are further regulated, the axial uniformity will slightly decrease, but it is still significantly better than the traditional tube expansion effect. It is worth mentioning that the bulging method proposed in this paper adopts single drive coil with simple structure and convenient toolingcompared to multi-coil electromagnetic forming systems. The actual effect of the bulging method will be further verified from the experimental level in the future. © 2024 China Machine Press. All rights reserved.