Optimal Design And Research On Structural Parameters Of Magnetic Pulse Welding Coils For Plate Parts

For energy shortage and environmental pollution problems,the lightweight of automobiles is especially important.There are two ways to realize the lightweight of automobiles: structure lightweight and material lightweight.Material lightweight replaces conventional steel through the use of lightweight materials such as aluminum and magnesium and their alloys.And thi s will inevitably involve joining techniques of dissimilar materials.As an efficient and environmentally friendly connection technology,magnetic pulse welding(MPW)has broad applications in the automotive industry.In the MPW system,the welding coil is the carrier of the discharge current,and its structure directly affects the magnitude of the electromagnetic force.Therefore,the coil is a key component of MPW system.However,the welding process involves many disciplines.It is difficult to compare coils from the theoretical analysis.In this paper,the method for calculating electrical parameters of special-shaped coils was proposed and the numerical model for MPW was established.Based on the corresponding calculation results,the performance of sin gle-sided welding coils with different structures(E-shaped,“?”-shaped and “? ”-shaped coils)was compared.The best coil structure was chose,and its parameters were optimized.The specific research is as follows:Firstly,COMSOL software was used to calculate the electrical parameters of single-sided welding coils with different structures.Then,based on the discharge current curve of the E-shaped coil and the electrical parameters of the E-shaped coil itself,the electrical parameters of the equipment other than the coil were obtained.And the equivalent electrical parameters and discharge current curves of coils under the same discharge energy were obtained.So far,the preliminary preparations for the numerical simulation had been completed.Secondly,the numerical simulation models of different coils were established.The PDV test results under the action of the E-shaped coil were used to verify the accuracy of the numerical simulation.Then,according to the numerical simulation calculation results,various data in the electromagnetic field and the structure field were compared.Due to the asymmetry of the structure of the “ ? ”-shaped coil,the current density and force were asymmetry.It was difficult to form a stable weld at the joint and the coil would be subjected to additional torque.The E-shaped coil and the“?”-shaped coil had similar performance in the electromagnetic field.Due to their symmetrical structure,the current density and Lorentz force were also symmetrical.Because of the difference in inductance and the number of side arms,the various values under the action of “?”-shaped coil were higher.In the structural field,both of them appeared stress concentration at the corners.The maximum stress value of the“?”-shaped coil was twice of the E-shaped coil.Therefore,the “?”-shaped coil was more likely to fail due to cracks.In addition,under the action of the “? ”-shaped coil,there were necking deformation at the edge of flying plates.The necking deformation reduced the strength of the welded joint.On the whole,the E-shaped coil structure is better.Finally,based on Isight and Minitab,parameter optimization of E-shaped coil was carried out.The side arm width,bottom width and coil thickness were extracted.And the sensitivity analysis was carried out to prove the rationality of parameter extraction.Subsequently,an approximate model was established and the NLPQL was used to obtain the parameter values of the optimal coil.Finally,the coils before and after optimization were compared in numerical simulation and experiment.The results showed that the optimal coil had excellent performance in current density,the speed of flying plate,joint tensile strength and energy saving.The optimization effect was obvious.In addition,the error between the simulated current density value of the optimized coil and the predicted value during optimization was very small,only1.91%.And the PDV speed measurement results and simulation results of each coil were within 5%.A series of results verified the accuracy of the numerical simulation and the effectiveness of optimization.