Multi-criteria optimization of weld bead in pulsed Nd:YAG laser welding of stainless steel 316

Laser welding is widely used for its advantages like deeper weld penetration, narrow heat affected zone, higher welding speeds and better weld quality with less damage to the workpiece compared to arc welding processes. The purpose of this paper is to determine the influence of major laser welding process parameters of beam pulse energy, travel speed and focal position on weld fusion zone geometry in stainless steel and optimizing these parameters to obtain maximum penetration and minimum weld width simultaneously. The experiments were planned according to Taguchi's L16 orthogonal array. The grey-based Taguchi method was then employed to convert the multiple quality criteria into one single relational grade. Based on the calculated relational grade, Taguchi tools such as analysis of variance and signal-to-noise ratio were used to analyze and obtain the significant parameters and evaluate the optimum combination levels of the mentioned process parameters. Moreover, the effect of optimization procedure was studied on the microstructure and micro-hardness of the weldments. It was concluded that this optimization method can lead to elimination of chain ferrite precipitation and more uniform micro-hardness across the weld bead. The confirmation experiments verified that this method can effectively improve multiple performance characteristics and the results are reproducible in laser welding.