An active vibration absorber for chatter reduction in machining

In the early days of the manufacturing industry, the limiting factor in obtaining higher material removal rates was 'Chatter', an unstable cutting condition with excessive vibrations. Maximum productivity can only be obtained using the knowledge of the theory of regenerative chatter. In the era of modem manufacturing industry, where the greater quality and productivity are increasingly demanded, especially the requirement to understand and avoid chatter is even greater. The key answering to this challenge is to increase the rate of material removal while maintaining stable cutting conditions through reducing chatter during machining operations. In this regard, an active vibration absorber can be used to effectively reduce the undesired vibrations of the structure, thereby increasing the border line of chatter stability. However, to date there has been little attention in applying this technique in the application ofmilling chatter suppression, especially for a flexible workpiece. In this thesis, the stability of milling process dynamics is theoretically investigated using the method of semi-discretization. An alternative means of improving stability in milling is also presented by developing the extended method of semi-discretization for the milling systems with variable time delay. This can be used to predict not only the stability but also the chatter frequencies for milling with irregular pitch cutters. Motivated by an interest in practically improving the stability margin in the milling process, a practical and straightforward active vibration control system with acceleration feedback is implemented using a proof-mass actuator. Based on the general framework of virtual passive control, three controller strategies are first demonstrated and evaluated through a laboratory based vibration study, consisting of virtual sky-hook damper, virtual passive absorber and virtual passive-active absorber. The· results indicate that virtual passive absorber control could be a simple and robust solution to the application ofmachining chatter reduction. Through the initial study of the theory of regenerative chatter, analytical optimizations of dynamic vibration absorbers are developed for application to chatter suppression. The performance of a virtual passive absorber to suppress workpiece chatter during high speed machining is then experimentally investigated for each tuning scheme, including the virtual sky-hook damper scheme. The results demonstrate that although the performance of the active milling chatter suppression system is limited by the actuator saturation, the chosen control strategy can provide at least a 6-fold improvement in the workpiece stability using a small actuator.EThOS - Electronic Theses Online ServiceGBUnited Kingdo