OBRABOTKAMETALLOV technology Vol. 27 No. 3 2025 from the nominal value ∆T and the amplitude of its change at the moments of AT fluctuations are also presented (Table 1, 2, column 11–12). According to the simulation results, at n = 630 rpm, the greatest increase in instantaneous temperature occurs when the cutting depth reaches its minimum value. At the same time, at the moments of fluctuations, there are combinations of parameters V, s, and t, at which their complex values practically level out the change in instantaneous temperatures (at V → max; s → min). It should also be noted that, as a result of vibrations under these processing conditions, the maximum instantaneous temperature may decrease relative to the nominal value (at V → max; t → max). When the cutting speed is increased, negative temperature deviations at moments of fluctuation are less pronounced or cease altogether. Thus, when turning at a speed of V = 343.6 m/min, for any combination of cutting mode parameters, the instantaneous temperature changes only increase (Table 2, column 11). The amplitudes of temperature spikes generally increase with an increase in spindle speed, and the factors contributing to the generation of positive temperature spikes also change. If at V = 216.5 m/min the main sources of temperature spikes with maximum amplitude are the moments of reaching extreme values of the parameters t and V, then at higher speeds, fluctuations in cutting depth and feed rate have a significant effect. Thus, when turning at V = 343.6 m/min, fluctuations with heating of the tool surface by an additional 61–70 °C occur more frequently, which is due to significant variations in the area of the cut layer due to vibrations characteristic of this machining mode. Table 3 shows the amplitudes of periodic temperature changes for different spindle speeds n. The highest values of the AT parameter at each machining speed are underlined, thus highlighting the cutting mode parameters whose fluctuations contribute most to the instability of the thermal state of the cutting zone at each value of n. The investigated speed range has a pronounced local minimum corresponding to a speed of 270 m/ min, for which the lowest values of the AT parameter are achieved at all extreme values of the turning modes. Increasing the spindle speed above this value leads to a change in the nature of temperature spikes (sources V, t are replaced by s, t) and an increase in AT amplitudes. Ta b l e 2 Variations of technological modes, cutting forces and main tribological parameters for V = 343.6 m/min Parameter state at the moment of fluctuation V, m/min s, mm/rev t, mm FXY, N l1, mm h, μm τк, MPa Ka Tmax, оС ∆T, оС AT, оС (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) nominal 343.6 0.198 0.5 142 0.24 14 319 1.962 1092.2 0 – V→max 345.4 0.17 0.507 149 0.21 15 386 1.967 1117.9 +25.8 32.8 V→min 343.5 0.158 0.47 139 0.19 15 423 1.974 1124.9 +32.8 s→max 344.2 0.207 0.509 205 0.25 20 430 1.959 1152.8 +60.7 60.7 s→min 344.5 0.151 0.47 119 0.17 13 382 1.975 1101.3 +9.1 t→max 344.7 0.168 0.519 194 0.21 19 496 1.966 1162.5 +70.3 70.3 t→min 343.8 0.157 0.45 139 0.18 15 447 1.976 1132.6 +40.4 Ta b l e 3 Calculated amplitudes of periodic temperature variations ΔT at moments when parameters V, s, and t reach extreme values Cutting parameters Amplitude AT, оС 216.5 m/min 252 m/min 270 m/min 294 m/min 318 m/min 343.6 m/min V 26.8 31.1 17.8 21.2 24.8 32.8 s 14.1 18.1 12.5 36.1 42.5 60.8 t 35.9 43.2 26.4 41.6 51.4 70.3
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