Application of Hilbert–Huang transform for vibration signal analysis in end-milling

Signals obtained in metal cutting are often non-linear and non-stationary, so that an appropriate signal-processing technique is needed for the process monitoring. In this paper, machining stability is evaluated by Hilbert–Huang transform (HHT), which can extract the features of vibrating signals. End-milling tests are conducted with thin-walled workpieces to demonstrates the feasibility of HHT in the monitoring for ever-changing state of machining processes. The experimental results obtained are as follows: HHT separated the signal containing chatter from others and can acquire the transition of frequency spectrum during the milling operation. Then, the effect cutting fluid and the influence by biting of hard material are investigated by HHT.