Optimization Of Soldering Process Of Traction Motor Stator Lead And Neutral Ring Resistance

In the practical operation of high-power asynchronous traction motor for railway vehicles,the lead wire of three-phase winding of the motor is often broken due to the influence of complex operating environment and periodic vibration of the locomotive.The traction motor stator leads and the neutral ring are generally connected by resistance brazing technology.The assembly method is that the two leads are distributed along the wide edge and then overlapped on the neutral ring.Only the first lead is usually broken.It is of great significance to improve the mechanical properties of the lead and the service life of the traction motor to study the fracture mode and failure reasons of the lead and optimize the assembly structure and process parameters of the joint.In this paper,the fracture form of the failed joint is analyzed,and the effect of welding temperature on the microstructure and mechanical properties of the lead is analyzed with the gradient annealing test of the original oxygen-free copper lead.Lead is studied through numerical simulation with different neutral ring assembly structure in the characteristics of the welding temperature field and thermal cycle,it is concluded that a better form of wiring and the corresponding process parameters,finally with the optimized way of wiring and welding process parameters for the actual welding,through actual welding joint organization and performance testing to verify the optimization results.The results show that the fracture of the lead occurs in the heat-affected area of the upper wire when the T-joint is overlaid,and the fracture is characterized by cleavage fracture,which is fatigue fracture.When the annealing temperature of oxygen-free copper leads exceeds650 ?,the microstructure grain grows and the hardness and strength decrease.When the current process of superposition wiring is adopted to weld the joint,the temperature field distribution of the joint is not uniform,showing the distribution state of low upper height,high in front and low in back.The temperature in the welding area and the heat-affected area of the two leads exceeds 650 ?.The temperature of the upper lead is always higher than that of the lower lead,resulting in serious softening problem of the upper lead.In order to solve the problem of uneven temperature field and ensure the current carrying capacity of lead wires,two new wiring methods are tried,namely parallel wiring and upper and lower wiring.The temperature field of parallel wiring is symmetrical to the left and right.The temperature field of the two leads is the same.The temperature field of upper and lower wiring presents symmetrical distribution,and the high temperature part appears in the area where the upper and lower leads contact with the graphite electrode.After comprehensive consideration of ensuring reliable connection of brazed joints and reducing the influence of welding heat cycle on the properties of base material,the optimal wiring method and process parameters obtainedare: horizontal wiring,welding current 2.22 k A,and welding time 4.8 s.The welding joint with new technology and structure can melt the filler metal completely.Compared with the old process,the grain size of the two leads is significantly smaller,the grain size at the end of the drill joint and the heat-affected zone is inhibited,the softening degree of the leads is reduced,and the hardness and tensile strength of the leads are obviously improved.