Study On New Welding Technology Of Butt Joint Of Metro Bogie Frame

Metro Bogie Frame is an important bearing body and power transmission component of metro vehicles,which plays a vital role in the safety of vehicle operation.However,the frame used in the subway is a complex structural welding component,with a large amount of welds,and multi-layer and multi pass welding process is adopted.Because residual stress and deformation will inevitably occur in the process of welding,which will seriously affect the dimensional stability and fatigue life of the frame.Therefore,it is necessary to study and develop the butt welding process package of frame with low stress,small deformation and high reliability and the backing methods of high-frequency pulse MAG welding and cold welding,analyze the evolution mechanism and control measures of post welding stress and deformation of multi-layer and multi pass welds,and study the reliability optimization design of welding sequence,It has very important academic value and engineering application prospect for promoting the technical development of frame welding forming and quality and the safety and stability of service application.In this paper,the butt welding process tests of S355J2 W weather resistant steel plate with3 mm gap and 12 mm thickness were carried out by using high frequency pulse MAG welding(cold welding backing)and conventional pulse MAG welding;By studying the changes of thermal cycle temperature,residual stress after welding,macro morphology,metallographic microstructure,hardness and mechanical properties of the welded test plate,and using SYSWELD welding simulation software,the temperature field and stress field in the welding process are numerically simulated and analyzed,and the excellent welding process parameters are obtained,which provides an experimental research basis for the welding of S355J2 W weathering steel of Metro Bogie Frame.(1)The weld forming quality is good and there are no welding defects.Both sides are welded on one side and formed on both sides.Compared with conventional pulse MAG welding,the microstructure of high-frequency pulse MAG welding joint is more ideal,because there is some acicular ferrite in the weld,the content of pre eutectoid ferrite is low,there is no side plate ferrite in the fusion zone,the range of heat affected zone is small and the grain coarsening degree is small.(2)According to the tensile test results,the tensile sample breaks at the base metal away from the weld,and the tensile strength of the welded joint meets the standard;The bending test results show that when the specimen is bent to 180°,the joint has no crack and meets the standard-The results of 40℃ low temperature impact test show that the impact energy of high frequency pulse MAG welding joint is higher than that of conventional pulse MAG welding,27.5 % and 23.5 % higher than that of weld and heat affected zone respectively;The fatigue test shows that the fatigue strength of high frequency pulse MAG welding joint is more than 5.7 %higher than that of conventional pulse MAG welding.(3)The welding thermal cycle curve obtained by numerical simulation of joint temperature field is very close to the measured value,and the overall trend is basically the same;The peak temperature of the temperature measuring point of high frequency pulse MAG welding is lower than that of conventional pulse MAG welding,and the cooling speed of the temperature measuring point is faster in the process of cover welding.The stress distribution obtained by numerical simulation of joint stress field is also consistent with the measured results.(4)Through the numerical simulation and comprehensive analysis of the temperature field,residual stress,macro morphology,microstructure,hardness,mechanical properties,temperature field and stress field of the butt joint of the welding test plate,the comprehensive performance of the welded joint of high-frequency pulse MAG welding(cold welding backing)is the best.