Process Research On Nuts Projection Welding Of Inverter Cabinet

Heavy haul locomotive haulage in the modern world railroad for bulk, bulkcargo transportation is the most important technical achievement, can save energyand reduce the pollution of the environment, which has the profound significance toour country’s sustainable development strategy. As the core device of train tractiondrive system, traction inverter directly influences the security and stability of theheavy haul locomtive, and presents high demand for the cubicle and assembly parts.Based on the nut welding inverter cabinet production as the research background,projection welding method is chosen as the welding method in order to avoid theshortcoming of MAG welding and TIG welding. Welding tests were conducted onQ235A nut and2mm thick hot rolled09CuPCrNi-A atmospheric corrosion resistantsteel, and obtained the optimal process. Through the study on the joint performanceand microstructure observation, the factors that affect joint properties and weldformation process were illuminated.Welding cracks, the black oxidation serious defects of nut root, electrodeadhesion and splash would occur in the joint when the welding parameters wereinappropriate. Adjusting the welding parameters and changing the parent metalsurface state can avoid these problems. Welding parameters, such as welding energyQw, welding time twand welding electrode pressure Fw, as well as the parent metalsurface state affected the joint strength. The best process parameters interval couldbe obtained through optimizing the welding parameters, which were removing theparent metal surface oxidation film,56~62%of the welding energy Qw,3~5cycles of the welding time tw,0.14~0.17MPa of welding electrode pressure Fw.Due to fast heating and cooling effect of resistance welding, the quenchedstructure formed in the joint. The highest hardness was obtained in the joint centerregion. With the increase of distance with the joint center, hardness showed adecline tendency. Increasing the welding energy Qwand welding time twcanincrease the joint hardness. The formation of solder joint can be divided into severalstages, which are, temperature increasing due to the heating effect at welding start,bumps melted and molten metal fills gaps under pressure, solid connection interfaceforms at the original convex point and sheet location under the effect of weldingelectrode pressure and molten metal solidified, the joint forms.Auxiliary pulse, such as preheat, slow cooling, or tempering pulse, can improvethe joint strength to some extent, but the effect is not obvious. Preheating, slowcooling and tempering pulse will affect joint welds hardness. According to the effect of reduce joint hardness and hardenability, the order could be preheating pulse, slowcooling pulse and tempering pulse. Through the joint fracture analysis, the fracturemode of single pulse welding joint is obvious brittle fracture. The fracture mode canbe transformed into plastic fracture through adding tempering pulse, which cansignificantly improve the joint plastic toughness.