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STFT-based induction motor stray flux analysis for the monitoring of cutting tool wearing in CNC machines

During a machining process, it is very important to carry out the corresponding tasks using cutting tools in a healthy condition, since the quality of the manufactured component can be seriously deteriorated when using worn tools, leading to a possible increase of production costs. Current methodologies are capable of monitoring and diagnosing the wear on the cutting tool adequately. However, in most of them the use of sensors located near the working area is necessary and indispensable, which in practical terms is not the most optimal solution since it is desirable to rely on non-invasive techniques. In this work, the impact of the use of worn cutting tools on the stray flux captured around the induction motor (IM) driving the spindle chuck is studied using time-frequency decomposition mathematical tools (and, more specifically, the short-time Fourier transform (STFT)). The experimentally obtained results show the appearance of some specific frequency components having considerable amplitudes for worn cutting tools, and also demonstrates the potential that this technique has to provide highly relevant information to determine the presence of worn cutting tools. Therefore, it becomes an excellent informational source for the diagnosis of these types of failures, taking advantage of its non-invasive nature.