Research On Uniformity Of Tube Electromagnetic Forming

Tube electromagnetic forming contains bulging and tube-compression. Due to the end effect, tube deformation is non-uniform along the axial direction. The realization of uniform deformation of tube has great significance to improve surface accuracies of workpiece and strength of the joints by EMF.The boundary conditions and axial symmetry of the electromagnetic field model were presented. The elastic-plastic FEM formulation was introduced, including yield criterion, hardening criterion and constitutive equations. The NEWMARK integration method was used in the solution of dynamics analysis, and the sequential coupled physics analysis method was chosen to solve the coupled field in the electromagnetic forming.The numerical simulation flow of the coupled electromagnetic-structural field was constructed with APDL in the FEM software ANSYS. Based on energy conversion, the discharge voltage of capacitors was estimated, and the current density was applied load. The flow can analyze the interactions of magnetic field, magnetic force and deformation. Based on uniformity criterion which was establishd, length range of uniformly deformed tube was obtained. With the analysis of different parameters, the results show that the discharge voltage and discharge frequency and material properties have hardly any effect on the uniformity of deformation, The coil length, the area of wire section and material properties have great influences on the uniformity. Because the distribution of discharge current is determined by the coil structure and the relative position between forming coil and workpiece, which cause the change of magnetic field and magnetic force, affect the uniformity of deformed tube.According to the simulation result, the influences of technological parameters on uniformity with different length coils were investigated. The results show that, there are uniformly deformed tube for the varied coils. For i.d 32 mm, o.d 42 mm bulging coil and i.d 56 mm, o.d 66 mm tube-compression coil, the proportion curves of uniform deformation have been obtained, and validated by theory and trials. there is a critical discharge energy for the deformation of tube.Moreover, reliabilities of numerical simulation are validated by experiments.