Parameter Optimization for Laser Ring Welding Dissimilar Steel Piston Rods
F-P. Yao, J-H. Li and T-Y. Liu
Laser ring welding is performed with a fibre laser on the shock absorber piston rod composed of 20Mn2 and Q345D in order to obtain better laser beam welding (LBW) process parameters to ensure welding quality with good shape, large weld depth and high surface strength. Laser power, scanning angular velocity and defocusing were taken as independent variables. Based on the orthogonal experimental arrangement the data is optimized in multiple ways based on the grey relational analysis (GRA) system theoretical model. Analytic hierarchy process (AHP) and GRA are used to calculate the influence of degree single-objective and multi-objective optimization. The simulation results show that the influence of each parameter on welding quality is scanning angular velocity, defocus amount and laser power. The final optimized process parameter combination is a laser power of 1500 W, a scanning angular velocity of 18 rad/s and defocus of –10 mm. The experimental results show that the optimized parameters increase the welding depth by 2.5 mm compared with the original parameters, increased the weld seam hardness from 470 to 530 HV and produced welds with no pores, cracks, arc craters or other defects in the weld morphology. Also, there was a lot of martensite and retained austenite in the microstructure so the strength and formability of the welds are enhanced. This optimization method can provide theoretical application and experimental reference for laser welding of piston rod.
Keywords: Fibre laser, 20Mn2 and Q345D dissimilar steel, piston rod, laser ring welding, weld morphology, process parameters, optimization, analytical hierarchy process (AHP), grey relational analysis (GRA)