Welding Technology And Numerical Simulation Of 160km/h EMU Body Side Wall With Low Stress And Small Deformation

With the rapid development of the rail transit industry,in order to ensure the safety,comfort and convenience of passenger transportation and realize the upgrading of 25T model express train with long distance and point-to-point transportation,160km/h power concentrated EMU was developed.As an important component of the train,the side wall has high quality requirements in the production process.Fusion welding and resistance spot welding is the initial technological means of side wall structure welding,will produce large residual stress and serious welding deformation after welding,which will adversely affect the appearance,performance and assembly accuracy of the car body,and it is difficult to meet the quality requirements of train operation.Cold arc welding and laser welding can realize thin plate welding with low stress and small deformation due to their low heat input,and have the advantages of no indentation,good sealing,excellent joint microstructure and high strength.This article mainly aim at low stress,small deformation welding process of the side wall.Using cold arc welding and laser welding to complete the welding process test,and analyze the microstructure and hardness distribution of welded joint and shear performance,discuss the influence law of parameters on joint performance with different welding process,and then extract the optimal laser welding process parameters.Thermal-elastic-plastic method was used to simulate the temperature field,stress field and deformation in laser welding process of"local"typical element,and the results were verified with the welding process test.After that,the natural strain method is used to simulate the residual stress distribution and deformation law of the side wall"integral"frame under different constraints.The results show that:Cold arc welding and laser seam welding joint shape is uniform,stable and without defects.The microstructure of arc cold welding joint is preeutectic ferrite distributed along grain boundary,and the ferrite in grain is fine strip ferrite,a little pearlite,acicular ferrite and granular bainite.The microstructure of laser seam welding joint is columnar crystal,the growth direction is perpendicular to the fusion line to the weld center,and the dendrite structure is near the fusion line.The hardness trend of arc cold welding joint is heat affected zone>weld zone>base metal,and the hardness trend of laser joint is weld zone>heat affected zone>base metal.The fracture zone of arc cold arc welding joint is located at the base metal side of Q310NQL2,and the joint has high strength and good quality.The fracture area of the laser seam welding joint is located in the weld,and the tensile shear is proportional to the welding depth and width.Through range analysis,the optimal level combination is P=2950W,V=60cm·min^-1,f=0mm.Through range and variance analysis,it can be seen that welding speed is the main factor affecting the maximum shear force of welded joints,and the effect is significant.The results of temperature field,stress field and post-weld deformation are in good agreement with the measured values.There is a"keyhole"area in the center of the weld,and the maximum temperature is up to 3100K.The longitudinal residual tensile stress is larger in the weld zone,and the transverse residual compressive stress is mainly concentrated at both ends of the plate.According to the simulation results of the natural strain method of the"integral"side wall,the welding residual stress is mainly concentrated in the weld zone and the intersection of beam and column.The side wall as a whole presents a"saddle"shape,and the welding deformation can be effectively controlled by applying different constraints.