Research On Electromagnetic Force Distribution And Material Forming Experiment In Tube Bulging Forming With Axial Compression

Although traditional mechanical pressure and hydraulic pressure forming technologies have been perfected,many problems will occur in the application of lightweight alloys,such as local fracture caused by poor ductility,stress concentration,and low forming limit,Prone to springback,cumbersome processes,etc.,due to various defects,the traditional forming technology is not suitable for light alloys.EMF technology can solve the problem of light alloy forming.The traditional one-coil electromagnetic has a single structure,which leads to serious wall thinning and mechanical strength reduction.restricted the further development of electromagnetic tube expansion and industrial application.In order to solve the problem of thinning the wall thickness of the workpiece during traditional one-coil electromagnetic tube expansion,some scholars have innovatively proposed a three-coil axial compression electromagnetic tube expansion method,that is,axial electromagnetic force and radial electromagnetic force bidirectional loading.The three-coil axial compression electromagnetic tube expansion can realize the axial compression of tube and solved the problem of the wall thickness reduction existing in the electromagnetic tube expansion of traditional single coil.However,its tooling structure is complex,and the matching between the coils is difficult,resulting in its expansion effect is not ideal.In order to realize the bidirectional loading of axial electromagnetic force and radial electromagnetic force more simply and effectively,In this paper,the two-coil axial compression electromagnetic tube expansion is proposed.In this method,two symmetrical electromagnetic coils are placed at both ends of the top and bottom of the tube,and achieve axial and radial electromagnetic force bidirectional loading.The change of the coil structure can change the direction and size of the electromagnetic force.Taking the coil structure as the starting point,the electromagnetic force and the forming performance of the pipe fitting are analyzed from the aspects of the basic principle of electromagnetic forming,multiphysics coupling and simulation.By optimizing the shape size of coils and the relative position of the coils to the tube,the top and bottom coils provide both axial and radial electromagnetic force.Thus can realize the bidirectional loading of axial electromagnetic force and radial electromagnetic and the coil structure can besimplified.The electromagnetic-structural coupling model of the tube electromagnetic expansion process was established using the finite element method,and electromagnetic force distribution law and tube expansion property of the traditional one-coil electromagnetic tube expansion,three-coil and two-coil axial compression electromagnetic tube expansion are analyzed.Further studied the coil geometry size the effect on the electromagnetic force distribution and wall thickness of the tube.The analysis result shows that when the inner wall expansion amount is the same,the two-coil structure can generate a greater axial electromagnetic force,and the wall thickness of the tube is reduced by 28.2% compared with traditional single coil.Finally,the two-coil axial compression electromagnetic tube expansion was carried out,which solved the problem of excessive wall thickness reduction of the traditional one-coil electromagnetic tube expansion and the complicated problem of the two-coil axial compression electromagnetic tube expansion.The experiment verified the correctness of the numerical analysis results.The experimental results show that two-coil axial compression electromagnetic tube expansion relative to three-coil axial compression electromagnetic tube expansion is greatly simplified because there is no intermediate coil,and the two-coil is easier to tooling and more operable.Compared with the traditional single coil electromagnetic tube expansion,the wall thickness reduction of the two-coil axial compression electromagnetic tube expansion are significant reduced under the condition that the expansion of inner wall is equal.