OBRABOTKAMETALLOV Vol. 25 No. 1 2023 technology Given the increasing demands on the quality of parts, it is worth focusing on the predictability of roughness parameters during machining, in this study – through correlation. Identified dependencies based on the value of the pair correlation coefficient in Table 2 indicate the possibility of influencing some of the obtained parameters through changing others and the presence of technological parameters predetermining the micro-roughness of the surface. Ta b l e 2 Calculated values of the pair correlation coefficients Compared values Correlation coefficient The existence of a linear relationship Linear connection Ф1 (Ra) R (Rz) 0.91 highly probable increases Ф2 (Rq) R (Rz) 0.92 highly probable increases Ф3 (Rt) R (Rz) 0.98 highly probable increases Ф4 (Rp) R (Rz) 0.93 highly probable increases Ф5 (γ) R (Rz) –0.41 very improbable decreases Ф6 (z) R (Rz) 0.40 very improbable increases Ф5 (γ) Ф6 (z) 0.00 doesn’t exist – Noted in theTable 2 correlations are significant at p < 0.05. It is generally accepted that a linear dependence exists if the modulus of the correlation coefficient corresponds to a value from 0.5 to 1. However, the value of the coefficient in the range of 0.3...0.5 may indicate the existence of a non-linear correlation [24, 25]. The regression graph of the parameter Rz (Fig. 8) indicates the confirmation of the above position. To assess the degree of influence of the angle of inclination on the amplitude parameter of roughness Rz, a multivariate regression analysis is carried out. The result of the analysis is a mathematical model (1), which characterizes the relationship between the value of roughness, feed per tooth, diameter and angle of inclination of the tool, expressed by the normalized model the graphical interpretation of which is shown in Fig. 9. 3 2.77 0.55 1.08 0.51 1 0.22 0 . .2 z z z z z f y D f f D D f D R γ γ γ = + − + − − + − (1) Fig. 8. Parameter Rz depending on the machining angle for a double-tooth cutter (Formulated by the author)
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