OBRABOTKAMETALLOV Vol. 25 No. 2 2023 technology that the calculation error of 23.99 % was obtained only at one point. The error in determining Kc at other points did not exceed 15 %. Thus, a point with an error of 23.99 % can be neglected. Since it was found that the calculation error according to the formula of the dependence Kc = f(Θ) is the smallest, the following dependence can be used to predict the effectiveness of the coolant by the lubricating action during friction of the 15% TiC–79% WC–6% Co alloy pad and the rotating roller made of steel 45 (0.45% C): Kc = 0.0069·Θ + 0.1308. (4) Thus, the method of accelerated evaluation of the lubricating properties of coolant used in metal cutting presumes the following algorithm: 1) apply a drop of the test coolant to the workpiece made of the required material using a pipette; 2) after the coolant drop has assumed a static position, fix its image using an electron microscope; 3) using a CAD software (COMPASS v18 or another similar one), draw a straight line on the resulting image, which is a projection of the surface of the workpiece, as well as a line that is a projection of the interface between the coolant drop and the surrounding air; 4) at the intersection point of the constructed lines, draw a tangent to the surface of the coolant drop; 5) measure the angle between the tangent line to the drop surface and the projection of the workpiece surface (wetting edge angle); 6) calculate the efficiency coefficient of coolant by lubricating action according to the formula (4) (for steel workpiece); 7) by the value of Kc, evaluate the efficiency of coolant. At the same time, the efficiency of coolant can be discussed if the value of Kc < 0. The smaller the Kc, the more effective the coolant is in terms of lubricating action. Conclusion After evaluating the results of the studies presented in this paper, the following conclusions were made. 1. In the work, the dependences of the coolant efficiency coefficient on the lubricating action determined for the friction between the roller made of steel 45 (0.45% C) and the pad made of 15% TiC–79% WC– 6% Co alloy on the coolant density and the coolant limiting wetting angle are established: Kc = f(ρ; Θ), Kc = f(ρ ) and Kc = f(Θ). 2. The greatest accuracy of calculations from 2.75 to 15% is provided by the formula of dependence Kc = f(Θ): Kc = 0.0069·Θ+ 0.1308. 3. The dependence Kc = f(Θ) is proposed to be used for the methodology of accelerated evaluation of the lubricating properties of coolant during friction of the 15% TiC–79% WC–6% Co alloy pad and the rotating roller made of steel 45 (0.45% C). The proposed method presupposes measuring the limiting wetting edge angle of a drop of coolant on the surface of the workpiece and calculating the derived empirical dependence of the coolant efficiency coefficient on the lubricating action. The lubricating action is one of the main, but not the only functional action of the coolant. Therefore, with different processing modes, the degree of influence of this action on the cutting process will be different. The use of coolant chosen according to the proposed method will have a positive effect, but the greatest effect will be under conditions when the lubricating action is dominant. For example, at low cutting speeds, when high temperatures do not occur in the processing zone and the lubricating effect overlays. References 1. Li G., Yi S., Li N., Pan W., Wen C., Ding S. Quantitative analysis of cooling and lubricating effects of graphene oxide nanofluids in machining titanium alloy Ti6Al4V. Journal of Materials Processing Technology, 2019, vol. 271, pp. 584–598. DOI: 10.1016/j.jmatprotec.2019.04.035.
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