Research On Laser Lap Welding Technology Of SUS301L Austenitic Stainless Steel For Railway Vehicles

For the manufacturing process of stainless steel vehicles by resistance spot welding, some problems have not been well solved up until now, such as larger welding distortion, poorer sealing of joints, lower static tensile strength, lower fatigue strength, and lower production efficiency. Because laser welding technique has many advantages, such as smaller welding distortion, faster welding speed, and better sealing of continuous welded joints. Therefore, in this study, a new method was proposed which carried out non-penetration laser lap joints of austenitic stainless steel for railway vehicles by means of changing the laser irradiation angle technology, and this strategy was also one of the innovations.The research object was austenitic stainless steel for railway vehicles, which was joined by a4kW continuous Nd:YAG laser using non-penetration laser lap welding technology. Heat conduction model of laser lap welding of austenitic stainless steel was established by using the three-dimensional nonlinear transient heat conduction differential equations. On the basis of the analysis of the physical processes of laser welding, the numerical calculation was made using SYSWELD welding simulation software, and the temperature field contours of upper surface and transverse section was obtained, the temperature cycle curve of melting zone, and the distortion distribution contours of the joints, et al.. Compared with the actual measurement data, it was found that the measurement data and simulation data were very consistent, which demonstrated that the high accuracy of the heat conduction model.In order to get laser lap welding joints of smaller distortion and higher strength, this study first proposed a non-penetration laser lap welding method, which utilized the changing the laser irradiation angle. Through the results of theoretical analysis and actual experiment, it can be found that changing the laser irradiation angle can easily get the joints of smaller distortion and higher strength. In addition, changing the laser irradiation angle could effectively reduce the fluctuation range of welding depth of the joints, and then improve reliability of the joints.In order to avoid the experimental errors generated by univariate tests since the relationship among the different factors were usually neglected, the multi-factors interaction tests research was done for the laser lap welding. Meanwhile, the mathematical formulas between input factors and response factors have been given using Design-Expert V7software. The verification results showed that the error range was less than5%. According to the mathematical formulas and the optimization goals, the optimal parameters range were obtained, as laser power of3.50-3.79kW, welding speed of7.40～8.00m/min, laser irradiation angle of65°, focusing distance of Omm, type of shielding gas of N2, and flux of30L/min.For the purpose of reducing the distortion of laser lap welding joints of austenitic stainless steel, this study first proposed a new laser orthopedic method which focused on angular distortion through the analysis of welding deformation feature and mechanism. Based on the numerical simulations and actual experimental studies of this new method, the laser orthopedic process parameters with optimal welding parameters were obtained, as laser power of0.15kW, scanning speed of3m/min, laser irradiation angle of90°, focusing distance of8mm, type of shielding gas of N2, and flux of30L/min, need to scan4times, and the scanning direction same as the welding direction. Through laser welding and laser orthopedic processing, using the optimal laser processing parameters, the angular distortion of welding joints can be reduced by0.88°to0.3°.Through the research of laser lap welding and laser orthopedic of austenitic stainless steel, the optimal laser lap welding joints were obtained, and compared them with the resistance welding joints. The comparison results showed that the static tensile force of laser welding joint with its width of40mm was23.326kN, about2.4times of the resistance welding joint. Under the same condition, and the confidence level of99%, the median fatigue life of laser welding specimens was about1.80-11.72times of the resistance welding specimens.Finally, through the research on this study, laser lap welding of0.8mm thick SUS301L-ST and1.5mm thick SUS301L-DLT austenitic stainless steel plate have been implemented with high efficiency, high strength, no discoloration and smaller deformation.