Multi-objective optimization of laser peening process parameters using Taguchi orthogonal array and gray relational analysis

Laser peening is one of the life-enhancing process that by radiation of laser pulse with sufficient energy at very short time on the surface of the metal results in the penetration of shock waves inside the material and the formation of compressive residual stresses inside it. The purpose of this research is the multi-objective optimization of the laser peening process parameters. Finite element method is used for modeling, Taguchi orthogonal array for design of experiment and the gray relational analysis for multi-objective optimization. The diameter, pressure, time, and overlap rate between two adjacent laser pulses are considered as design factors that change in 4 levels and the Taguchi L16 orthogonal array is used for experiments layout. The average residual stress at the surface of first pulse, minimum and maximum residual stress and the mean of the residual stress depth in the center of two laser pulses were considered as optimization target functions. By performing a gray-relational analysis, the Gray relational grade for each experiment was calculated and the optimal level of each parameter was obtained. The results indicate that the optimal state of each parameters of diameter, pressure, time and the overlap rate between the two laser pulses are at the fourth, fourth, first and fourth levels, respectively are 8 mm, 4 GPa, 30 ns and 75%. Also, analysis of variance was performed on the results to determine the effect of each parameters on the output that the laser time with 58.87% is the most effective parameter on the results.