Short-Time Fourier Transform Method in AE Signal Analysis for Diamond Coating Failure Monitoring in Machining Applications

Coating failures due to delaminations are the primary life-limiting criteria of diamond-coated tools in machining. Process monitoring to capture coating failures is thus desired to prevent from poor part quality and possible production disruption. Following previous studies of AE signal analysis for diamond coating failure monitoring in machining applications, this research applied a short-time Fourier transformation (STFT) method to capture the coating failure transition during cutting. The method uses sub-divided signal segments, in a continuous manner, for the fast Fourier transform (FFT) analysis and computes the amplitude ratio of high vs. low frequencies as a function of cutting time during a cutting pass. The results show that during the coating failure pass, a clear sharp increase of amplitude ratio (value change over one) of high/low frequency occurs along the cutting time. On the other hand, the amplitude ratio only exhibits a certain low range fluctuations in other passes, e.g., initial cutting and prior to failure passes. Thus, it can be suggested that the applied STFT method has a potential for diamond coating failure monitoring. However, for coating failure associated with a smaller tool wear (less than 0.8 mm flank wear-land width), the amplitude ratio plot from the STFT analysis may not clearly show the failure transition.