Thin-walled workpiece tends to vibrate easily because of its weak rigidity in machining process. Non-linearity in machining thin-walled workpiece makes it difficult to predict the vibration, and there is no precise theoretical model previously. To understand the vibration behaviour in milling thin-walled workpiece, a dynamic vibration monitoring model of cantilever workpiece is proposed based on modal theory, in which vibration of any point on cantilever beam considering N order modes can be monitored by dynamic displacements measured by N sensors. Taking a cantilever plate as an example, an on-line vibration monitoring method for workpiece vibration during milling process is proposed by adopting a polyvinylidene fluoride (PVDF) film sensor as the displacement sensor. From the analysis of signal in time-frequency domain, it can be concluded that PVDF thin film sensor can monitor periodic resonance signals and high-frequency vibration signals, and high-frequency vibration is easy to occur in entering, exiting stage which frequency is scattered in the vicinity of frequency multiplication of periodic cutting excitation. Finally, only considering first-order mode of the workpiece, vibration of interaction point on workpiece between workpiece and tool is calculated and by comparing with the relieving amount of workpiece due to deflection, validity of the method is proved.
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