OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 4 4 2 Fig. 10. Spectrograms of initial processing stage with use GW 2 and St1 = 0.01; St2 = 0.015; St3 = 0.02 mm/double stroke Fig. 11. Spectrograms of final processing stage with use GW 2 and St1 = 0.01; St2 = 0.015; St3 = 0.02 mm/double stroke signals are presented in the form of spectrograms of acoustic vibration frequency distribution for various process conditions and subject to comparison. No significant and stable acoustic excess kurtoses are observed in the high-frequency range (>8 kHz). Furthermore, analysis of the spectrograms of the idle operation of the setup showed that significant excess kurtoses appear in the low-frequency region of the spectrum (˂1,000 Hz). To this end, we considered the spectrograms in the range of 1–8 kHz. The spectrograms of the initial processing stage (Fig. 8, 10) differ from the idle operation spectrogram in terms of new excess kurtoses. An additional source of acoustic vibrations here is only grinding (removal of surplus) with a dressed wheel. This process can be observed in the spectrograms in the form of increases in the amplitude of the sound level in the range of 1,400–2,000 Hz for processing with GW 1, and in the range of 1,400–2,400Hz for processing with GW 2. It can be concluded that the applied acoustic method is sensitive to the process under study. The initial stage is also characterized by weak differences in the spectral compositions for different values of the periodic vertical feed. This applies in particular to the process using GW 1. Wheel surface diamond dressing involves a running-in stage. This stage can vary in duration depending on the periodic vertical feed, but the same mechanism for transforming the tool surface due to the removal of unfavorably oriented abrasive grains. At the final stage, processing is performed with a tool, which has lost its original characteristics and has reduced cutting capacity. While the normal operation stage [27] corresponds mainly to the wearing of the peaks of abrasive grains and surface chipping, in the moment under consideration (emergency stage) it is already characterized by bulk failure of the grains and shearing from the bond. Intensively increasing tool wear and a decrease in its cutting capacity have the following manifestations in the spectrograms of the final processing stage (Fig. 9, 11). We can see a significant increase in the amplitude of the sound level in a wide
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