OBRABOTKAMETALLOV technology Vol. 24 No. 1 2022 8]. In this connection, temperature is associated with such a factor as wear intensity and is further used as a limiting factor in determining rational (or optimal) cutting modes [5] (Figure 1). Figure 1 shows that the minimum wear rate of the tool for 70% Ni-Cr-W-Mo-Ti-Al and 70% Ni-Cr-WMo-Ti-Al-Nb alloys is the same and corresponds to a temperature value of about 750 oС at a cutting speed of 25 m/min. Fig. 1. Dependence of the wear rate of the cutter and the cutting temperature on the type of workpiece and cutting speed [5] So there are recommendations [5, 9], according to which it is expedient to assign cutting modes, maintaining rational (optimal) temperature values. In the work of A. D. Makarov [5], it was proposed to take into account the effect of cutting temperature on cutting speed. He formulated the principle that with various combinations of cutting speed, feed and depth of cut, a constant temperature in the cutting zone (optimal temperature) can be found, corresponding to the minimum average wear rates. In a number of works [10-12], the cutting temperature was determined either experimentally (by the method of natural – artificial thermocouple), or theoretically [6, 13]. Temperature measurement by experimental methods in production conditions is inefficient and leads to great difficulties. These difficulties are primarily associated with setting up expensive equipment for constantly changing cutting conditions (for example, the material of the workpiece has changed, the geometry of the cutting tool has changed, etc.) and calibration of the received thermal EMF signals (for thermocouples). If temperature measurements are made by non-contact methods (thermal imagers), then in this case there is a need to calibrate constantly the device when changing the processed material and to produce constant focusing when the cutting tool moves. In addition, it is impossible to measure the temperature by non-contact method when milling using coolant, or when the cutting zone is closed by the processed material, or chips. In this connection, it is advisable to use programs (methods) that allow theoretically calculating (predicting) the temperature for a certain group of processed materials, taking into account the influence of changes in mechanical characteristics during the cutting process, without resorting to a large number of experiments. Thus, Ezel et al. [14] proposed a theoretical model for calculating the temperature for high-speed end milling of die steels based on the finite element method. Based on the experimental data, the coefficients of the model were obtained, which were included in the DEFORM-2D software. Thus, the numerical method was limited to a specific material and specific machining conditions, and accuracy was compromised by assuming that the yield strength of the material is independent of strain, strain rate, and temperature during the milling process.
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