OBRABOTKAMETALLOV Vol. 27 No. 1 2025 technology µ ⋅ ⋅ ϕ = µ ⋅ = 0 sin 2 fr N Ð F P , (4) where µ is the empirical coefficient of friction. After transformation, we obtain: µ = + ⋅ ⋅ ϕ 0 0 4 ( ) fr Ì Ð D d sin . (5) Then, using the maximum values of the friction torque, as well as the applied axial force, the empirical coefficient of friction for the considered case is determined. Results and their discussion The measured friction torque Mfr at a constant axial load P0 = 2,000 N using various metalworking fluids (MWFs) is presented graphically in Fig. 5. Analyzing the obtained data (Fig. 5), the maximum empirical coefficient of friction (μ = 0.48) was observed under “dry” friction conditions, without MWF. The addition of NMA as a modifier to MWFs reduces the empirical coefficient of friction. The most significant reduction occurred with sunflower oil (μ = 0.11) compared to mineral oil-based MWF (μ = 0.19). This suggests that the sunflower oil-based MWF with NMA exhibits improved lubricity, providing boundary lubrication, and possibly even liquid lubrication. Fig. 5. Empirical friction coefficient (μ) values in various MWF environments Therefore, sunflower oil modified with NMA is the most effective MWF, compared to sunflower oil without NMA, mineral oil I-20A without NMA, and mineral oil I-20A modified with NMA. This indicates the high lubricating and bearing capacity of the experimental MWF. Determining the empirical friction coefficient using the described methodology provides a quantitative assessment of the tribological properties of the modified MWFs and allows for a more comprehensive understanding of the influence of modifiers, in this case NMA, on the friction force. Following the investigation of the influence of modified MWFs on the empirical friction coefficient, the cutting force during drilling was determined using similar MWFs. To accomplish this, an experimental
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