Research On The Technology And Reliability Of Micro-resistance Welding For Long Life Conducting Ring Brush

In recent years,in the aerospace,weapon,medical devices,microwave devices and other fields,with the development of lighter and smaller electron devices,the requirement for microstructures with greater function,smaller scale and higher reliability has been increasing.For the connection between microscale wire and nanoscale plating,traditional bonding methods,which have their unique shortcomings,are becoming more and more dissatisfied,and a new bonding method is urgently needed to be developed.In this paper,micro resistance welding is developed to solve the connection between wires and the brush blades in collector rings,and product the micro joint with great function and good quality.For Au Ni9 brush wires with three different diameters and beryllium bronze alloy brush blade,traditional electrode was improved and the appropriate welding structure was designed.Based on the average shear strength of welding joints,the process parameters were optimized,and the influence of process parameters on the quality of welding joints was studied.The finite element software was used to simulate the micro-resistance welding process,the current-carrying reliability tests and the random vibration test.The results show that the quality of the micro-resistance spot welding joints wtih coating is significantly improved compared with that formed without coating.In this test,the Ni coating was used and the electroplating process was adopted.The current density was 3 A / dm2 and the thickness of the coating should be between 5 and 20 ?m.The optimized process parameters were 0.55 k A-15 ms,0.85 k A-25 ms and 0.95 k A-20 ms,and the average shear strength of corresponding joints were 0.74 kgf,3.22 kgf and 5.32 kgf.The most influential factor of joints is the welding current,with which became larger the area of joint was bigger.For brush wires with the same diameter,the shear strength of joints was larger.The fracture location was between the coating and the brush blade,and the fracture area increased with the increase of welding current.The scanning results of the micro section of the welding joint show that the interface area was larger and smoother with less defects under the bigger welding current.In the process of micro-resistance welding,the recrystallization process happened at the welding interface.The larger the melting area was,the thicker the equiaxed crystal area was.The diffusion of Au atom and Ni atom was driven by atomic concentration and the electric field force.The larger the welding current was,the farther the diffusion distance was.The change of welding time has little effect on the migration distance of elements.The modal calculation results of random vibration reliability test show that the first eight natural frequencies of joints are smaller than 150 Hz.The spectral analysis results show that the dangerous point of the joint is located in the mutation of the joint,and the fatigue damage degree is small.The simulation results of current aging reliability test show that the current accumulation phenomenon occurs at the bottom of solder joint,and the maximum current density value can reach 3.16 × 105 A / cm2,which has the risk of electromigration failure.