On the issue of selecting and optimizing parameters of continuous laser welding of cast iron

Introduction. Cast iron extremely poorly tolerate thermal welding cycles, and therefore it is necessary to choose carefully the technological parameters. The main parameters of continuous laser welding are: the power of laser radiation, the welding speed, the parameters of the focusing system. The aim of the work is to determine the optimal power and speed of continuous laser welding of cast iron, depending on the geometry of the weld. In this paper, the welding seams obtained on samples of gray alloyed cast iron with a pearlitic metal base, using an LS-1 ytterbium fiber laser, are studied. Research methods. The geometric parameters of the joints were quantified in the program for quantitative analysis and image processing ImageJ. The obtained data were processed by regression analysis. To optimize the process parameters, an orthogonal plan of the passive experiment was developed, including nine experiments in which the factors varied at three equally spaced levels. The quality parameters in the passive experiment were the geometric dimensions of the weld pool and the size of the quenched zone. To solve the optimization problem, we used the methods of gray relational analysis and linear programming. Results and Discussions. The obtained regression models explain a significant proportion of the variance of the dependent variables, the regression coefficients, as well as the models themselves, are statistically significant, which indicates a close linear relationship between the seam geometry and the process parameters. The calculated shape of the weld pool depending on the radiation power and welding speed shows that the required welding seam of the required dimensions can be obtained at various process parameters which allow solving a multi-criteria optimization problem. The gray relational evaluation of the geometric parameters of the seam shows that the most correct parameters in terms of obtaining the seam of the maximum depth with the minimum width, convexity (concavity) and the quenched zone are the minimum power and maximum welding speed. The calculation of the optimal radiation power and welding speed depending on the seam depth showed that welding of small thicknesses is optimally carried out with minimal power, and the seam depth is adjusted by changing the beam speed. Welding of large thicknesses is optimal at high speed, and to increase the depth of the seam, the power must increase.