Tool wear evaluation in drilling by acoustic emission

Abstract A drilling process with different degrees of wear in the drill bit was studied to find relationships between acoustic emission (AE) and torque measured during the drilling process, and also with the degree of wear of the tool. SAE 1040 steel samples were drilled, making holes with 5 mm diameter twist drill bits in continuous feed. The drill bits were modified with “artificial” (produced by spark-erosion) and “real” (obtained by regular mechanical use) failures such as different degrees of wear in the cutting edge and the outer corner. For every drilled hole, torque and AE were simultaneously measured and acquired. In the first part of this work, the correlation between the AE parameters and torque measured during the drilling process is studied. Torque was measured as a control parameter to follow the dynamic behaviour of the drill bit. An alternative AE feature, called Mean Power (MP) showed a good correlation with torque when the moving average (MA) was computed. In the second part, the AE mean power (MP) was related to different degrees of wear in drill bits. Clusters for the different levels of wear in a 2-D plot were obtained. In that plot the moving variance of the MP vs. the moving average of the MP, for each case of wear, were represented. This application aims at repetitive manufacturing operations, where many signals per second may be obtained with fixed parameters as shape, drill bit diameter, spindle speed, feed, and a good statistical study can be done.