## 3 Results of Studies of AE Signals  
### Results of Studies of AE Signals during Blade Processing  
When monitoring blade machining, the most significant interest is in the response of AE signals to changes in the state of the tools. These include wear on cutting edges, chipping, and breakage. In [53], the deformation processes of chips and the surface layer were studied using experimental research and calculations. Figure 7 shows an example of calculating the field of strain rates during chip formation using the Deform program (DEFORM-2D V.8.1). It can be seen that the highest strain rates are located in the vicinity of the conditional shear plane, which is formed from the cutting edge and propagates towards the interface between the surfaces of the workpiece and the formed chip. Tool wear in calculations using the Deform program was simulated by changing the radius of the cutting edge (r). Its increase leads to an expansion of the region covering areas with significant strain rates, and, hence, to a rise in energy costs for forming these regions. The figure also shows that some areas with different strain rate intensities remain in the surface layer, saturating it with an abundance of dislocation accumulations and microcracks. The exact figure shows the intensity of deformation of the surface layer (\(\epsilon_{\text{int}}\)) along the depth of the layer (\(\delta\)). The bottom line corresponds to a tool with a radius of 0.02 mm, and the top line corresponds  
Figure 5: Installation for surface doping “RITM-SP” (**a**) and the scheme of the channel for recording vibroacoustic signals (**b**): 1—vacuum chamber; 2—vacuum input; 3—workpiece; 4—wire waveguide; 5—receiving plate; 6—accelerometer KD-35 with magnet; 7—preamplifier RM-3; 8—amplifier VShV-003 (Izmeritel Ltd., Taganrog, Russia); 9—external ADC module model E440 (L-CARD Ltd., Moscow, Russia); 10—recording computer. Figure 6: Installation of the accelerometer in the processing area of the WEDM machine CUT 30P: 1—worktable; 2—special stand; 3—accelerometer on a magnet; 4—workpiece; 5—wire electrode. to a tool with a radius of 0.12 mm. It simulates the wear limit. It follows from the graphs that with increasing tool wear, the deformation of the surface layer increases by more than two times. For deeper layers, the difference in the magnitude of deformations is leveled out. Figure 8 shows the results of experiments to determine the intensity of deformations during turning with cutting plates with different degrees of wear. The measurements were carried out using the technique of applying coordinate grids to the cross-sectional surface of the workpiece, the deformation of which was measured after removing the chips [53]. Experiments were carried out for five cutters with different wear. The view of the cutting edge from the back edge for cutters with minimal and maximum wear is shown in the photographs in Figure 8.  
Comparing the graphs in Figures 7 and 8, it can be noted that in a full-scale experiment, the deformation values decrease faster; at a depth of 0.2 mm, they are almost invisible. It should be noted that the ratio of the deformation of the surface layer for sharp and excessively worn cutters during full-scale tests was 7-8 times, which significantly exceeds the calculated ratio. This suggests that modeling wear as a cylindrical surface does not correspond to the actual wear shape. Figure 9 shows the octave spectra of AE signals covering the range up to 11 kHz when turning 41 CrS4 steel with the same modes of a sharp (1) and worn (2) tool (photos of the cutter edges are shown in Figure 8). On the graph, it can be noted that in the spectrum of the VA signal, when working with a worn tool, the amplitudes at high frequencies fell, and the amplitudes in the low frequency range increased. This distortion of the AE signal spectrum shape was proposed to be assessed by the amplitude ratio (K\({}_{\text{f}}\)) in different frequency ranges [47; 48; 49; 50; 51; 53].