## 4 Results and Discussion  
Works [49; 53; 56] consider the issue of the phase transformation of matter under the impact of laser pulses of different powers. A comparison of existing ideas about the effect of an increase in pulse power density on the transition of a substance to the stages of melting, evaporation, and ionization with the behavior of the parameters of AE signals allowed us to draw a particular conclusion. The meaning of this conclusion is that with an increase in the power density of the thermal effect on a substance, the RMS amplitudes of the AE signal increase in the high frequency range, which is faster than the increase in the RMS amplitudes in the low frequency range. This result is reflected in a drop in the K\({}_{\rm f}\) parameter with an increased heat flow power density. This conclusion was confirmed by the results of experiments with EDM processing and electron beam processing. For example, Figure 13b shows records of changes in the components of the AE signal in the high and low frequency ranges during the WEDM processing of the HG20 alloy. The recording was carried out from the very beginning of cutting until the wire electrode broke. The reason for the break was that erosion products gradually accumulated in the gap between the electrodes, which absorbed part of the energy of the discharge pulses. As a result, the valuable power density decreased and the proportion of evaporated substance decreased. In this case, melted material accumulated on the electrodes, and the gap between the electrodes was reduced, causing a short circuit. Subsequent heating of the electrodes led to a loss of strength of the wire electrode and its breakage. Figure 13c shows how the K\({}_{\rm f}\) parameter changed by the time of the break. If the machine had an acoustic monitoring system, it would have been possible to prevent electrode breakage by promptly stopping its feed and carrying out relaxation to remove erosion products from the gap. The situation with electron beam processing is very similar to what was observed when exposed to laser pulses with different power densities (Figure 14b). The difference lies in the heat flow carriers. An increase in the power density of the electron flow causes increased evaporation of the doping coating [53; 54; 55; 56; 57]. To prevent its complete evaporation, it is necessary to limit the discharge voltage of the electron gun. Thus, an increase in the discharge voltage corresponds to a rise in the power density of the heat flow and is accompanied by an increase in the proportion of evaporated material. Evaporation processes cause an increase in the energy of acoustic radiation at high frequencies, which determines the drop in the K\({}_{\rm f}\) parameter shown in Figure 14b. The ability to monitor the parameters of AE signals is beneficial when debugging new technological processes with unstudied properties of doping coating materials [49; 50; 57]. Figure 16: Change in the RMS of the amplitudes of the AE signal in the octave bands of 8 and 16 kHz and the K\({}_{\rm f}\) parameter when exposed to laser pulses with different power densities q\({}_{\rm s}\) on a steel workpiece. If the connection between the features of changes in the parameters of AE signals and changes in power density and, accordingly, the proportion of evaporated material during processing with concentrated energy flows is clear, then the connection between acoustic parameters and wear of a blade tool needs an explanation. In this case, there are no thermal pulses, the power density of which can be associated with changes in the parameters of the AE signals. From the theory of spectral analysis of pulse signals, it is known that the frequency of the upper limit of the decomposition of a pulse signal into a spectrum containing the bulk of the pulse energy is inversely proportional to the pulse duration [58]. The mechanisms of changing the time of pulses during cutting can be different. The main ones include the following:  
1.