The use of the Hilbert-Huang transform in the analysis of machining vibrations in machine tools

This paper presents a research on the effects produced in a induction motor torque while it is driving a machine tool working in a metal cutting process. The machine tool used in the investigation was a lathe. The research is based on two data acquisition processes, the first using a Kistler stationary dynamometer and the second using an induction motor torque estimator. Both datasets acquired were processed with use of the FFT and the Hilbert-Huang transform algorithms. The FFT algorithm has been used for a long time in the analysis of vibrations processes and its stationary characteristic is very well known. The Hilbert-Huang transform (HHT) is an adaptive method that includes the properties to analyze non-linear signals and properly performs the supplying of the lacks of FFT method. The HHT method has an empirical basis that is the Empirical Mode of Decomposition (EMD) process, but is a powerful tool to perform vibration analysis. The main target of the project was verify if the monitoring of the machining process by observation of the torque estimated by measuring the electrical quantities of the mains against the dominant cutting force measured by a specialized equipment is good enough to justify the use of the method in industrial machine tools.