# A Method for Identifying the Wear State of Grinding Wheels Based on VMD Denoising and AO-CNN-LSTM
## 3 Experiment
### Classification and Calibration of Grinding Wheel Wear States  
The extent of wear on the grinding wheel has a direct impact on the quality of the workpiece surface grinding. Consequently, surface roughness serves as an indirect indicator reflecting the sharpness and wear condition of the grinding wheel. Throughout the grinding process, abrasive grains continually cut and scrape the workpiece surface, removing material and leaving scratches. As abrasive grains lack a strict arrangement pattern and exhibit a random distribution on the grinding wheel's surface, grains with varying exposed heights interact with the workpiece simultaneously, resulting in diverse material removal amounts across different regions of the workpiece surface. This randomness leads to the formation of random roughness on the processed workpiece's surface [24]. Blunted abrasive grains possess weakened cutting performance, unable to effectively remove material to form cutting but instead causing material squeezing on the workpiece surface, resulting in localized elevations. The grinding process induces stress and frictional heat, leading to elastic, plastic deformation, and thermal deformation. This, in turn, contributes to unevenness in height across different regions of the workpiece surface [25]. In the grinding experiment conducted in this paper, the variation in surface roughness of the workpiece at each node is illustrated in Figure 8.  
Figure 8: Surface roughness variation of the workpiece at each node. Figure 7: Grinding Wheel Experiment Workbench. The first wear stage corresponds to nodes 1-2, where the surface roughness of the workpiece is relatively low and exhibits a slight decrease. During this stage, the new grinding wheel undergoes initial grinding, and the friction and compression between abrasive grains and the material lead to rapid micro-fracture of these abrasive grains. Additionally, the wear area at the top of some abrasive grains increases. Consequently, the grinding wheel experiences rapid wear in this stage, and the distribution of abrasive grains on the grinding wheel gradually becomes more uniform. Therefore, the removal of material from the workpiece surface is relatively even, resulting in lower surface roughness. The time-domain waveform of the acoustic emission signal during this stage is depicted in Figure 9, characterized by a relatively small amplitude. Thus, this stage is identified as the initial wear state of the grinding wheel. The result of applying VMD denoising to this typical signal is shown in Figure 10.  
The second wear stage corresponds to nodes 3-7, where the surface roughness of the workpiece is relatively low and exhibits a gradual increase. During this wear stage, the wear area at the top of the abrasive grains further expands, and a small portion of the abrasive grains shows signs of fracture or even detachment. Due to the relatively stable condition of the abrasive grains on the grinding wheel during this stage, the amount of  
Figure 10: Typical AE signal of initial wear after VMD denoising. Figure 9: Typical AE signal of initial wear. wear on the grinding wheel is relatively modest. The grinding performance of the wheel experiences a slight weakening, resulting in a gradual increase in the surface roughness of the workpiece. The time-domain waveform of the acoustic emission signal during this stage is depicted in Figure 11, featuring a noticeable increase in amplitude that tends to stabilize. Thus, this stage is identified as the intermediate wear state of the grinding wheel. The result of applying VMD denoising to this typical signal is shown in Figure 12.  
The third wear stage corresponds to nodes 8-10, where the surface roughness of the workpiece is significantly higher and undergoes a rapid increase. In this wear stage, the wear area at the top of some abrasive grains has become very large, leading to a sharp increase in grinding force and the substantial breakage, fracture, and detachment of numerous abrasive grains.