基于PVDF薄膜传感器的薄壁件铣削振动在线监测与分析

On-line Vibration Monitoring and Analysis of Thin-walled Workpiece Based on PVDF Film Sensor in Milling Process

薄壁件的弱刚性导致其在加工过程当中容易产生振动,而薄壁件加工过程中存在的非线性问题使得加工振动难以预测,尚无法建立精确的理论模型。为了研究薄壁件铣削加工过程中的振动,提出一种基于模态理论的悬臂梁工件的动态振动监测模型,利用N个动态位移传感器监测前N阶模态下悬臂梁上任意一点的振动。以铣削加工悬臂薄板为例,采用聚偏氟乙烯(Polyvinylidene fluoride,PVDF)薄膜传感器在线监测了铣削过程中工件的振动位移。工件振动位移信号的时频域分析结果表明,PVDF薄膜传感器能够有效监测薄壁件加工过程中周期谐振信号和高频振动信号,其中高频振动易发生在切入、切出阶段,且频率多分散在周期性切削激励倍频附近。最后,只考虑工件一阶模态,计算得到刀具在工件上动态作用点处工件的振动位移,并与工件变形引起的让刀量对比,验证了该方法的有效性。

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.