Nanosecond laser ablation of micro-pits in Ni60/WC coatings with coupled thermal-stress simulation and parameter optimization

Abstract

In order to solve the problem of crack sprouting inside the micro-pit caused by improper design of laser ablation process parameters, this study establishes a thermal-stress coupling simulation model of nanosecond laser ablation of micro-pits on Ni60/WC coated surfaces. It researches the influence of laser process parameters (laser power, scanning speed, processing times) on the index parameters of micro-pit diameter, depth, and maximum residual stress. The weighting of diameter, depth and maximum residual stress sub-objectives in the comprehensive evaluation objectives of micro-pits are calculated. The response surface method of Central Composite Design (CCD) and regression analysis are used to fit the response surface functions of micro-pit diameter, depth, and maximum residual stress as a function of the variation of laser ablation process parameters. The Genetic Algorithm (GA) is used to minimize value of the maximum residual stress sub-objective function and to optimize the process parameters of laser ablation of micro-pits, using the values interval of the micro-pit diameter and depth functions as nonlinear constraints. The results show that the maximum residual stress varies quadratically with laser power and scanning speed, increases linearly with the processing times, and is coupled with the ablation process parameters. A design method for optimizing the parameters of nanosecond laser ablation by maximum residual stress is established, and the process parameters are optimized to meet the design parameters and quality requirements of micro-pits: laser power of 12 W, scanning speed of 276 mm/s, and 4 times of processing. The optimized process is provided for the parameter tuning nanosecond laser ablation of micro-pits on Ni60/WC coating surfaces.