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

OBRABOTKAMETALLOV Vol. 23 No. 3 2021 technology Fig. 2. Microstructure of sample No. 4 heating and cooling rates increases a hardening zone from the solid phase, which has a brittle martensitic base. Together, these factors add to the risk of transverse cracking in long weld seams. Reducing the laser power and welding speed allows providing cast iron melting without its intense boiling and vaporisation. In this case, complete dissolution of graphite inclusions is possible. The weld bead of the required dimensions can be obtained at various powers and welding speeds (Fig. 3). The choice of the optimal technological parameters that ensure a high-quality seam is a multi- criteria optimization problem. On the other hand, it would be desirable to carry out a welding process at a minimum power and at a maximum speed. In the optimization problems for several dependent variables (penetration, width, weld convexity, hardening zone thickness), assessing a certain complex quality indicator is required. To resolve the issue of power and welding speed optimal levels, the method of grey relational analysis was chosen [19, 20]. An orthogonal matrix (9×2) was constructed, which was a passive experiment, consisting of 9 experiments, in which the factors varied at 3 equidistant levels. The experimental design and the geometric parameters of the weld seams calculated using regression models (Table 2) are presented in Table 4. The initial data for the analysis should be normalized. The melting zone penetration was normalized in accordance with the “bigger is better” principle according to the formula: − = − max max min j ij ij ij j ij j ij y y x y y where y ij – is the value of the i-th parameter (penetration of the melting zone) in the j-th experiment. Other geometrical parameters of the weld seam are suitable for the “less is better” characteristic: − = − min max min ij j ij ij j ij j ij y y x y y The degree of discrepancy between the ideal (best) and experimental settings is expressed by the value of gray relational coefficients, which are calculated by the formula: