Identification and control of an active boring bar using VCA actuator

Boring operations due to the large length to diameter ratio and the high flexibility of tool are prone to self-excited (chatter) vibration. This vibration may cause poor surface quality, low dimensional accuracy and tool breakage. In practice, chatter is the main limitation on production rate. The main reason of chatter phenomenon is the dynamic interaction between cutting process and structure of machine tool. By increasing the length of the cutting tool, the vibration tendency in the tool’s structure increases. Improving dynamic stiffness of the tool is the most effective solution for decreasing vibration and increasing chatter stability. For increasing the stability of the tool in long overhang boring operations, passive and active vibration control has been proposed and implemented. In active control methods, vibrations can be effectively damped over a various cutting conditions. The aim of this research is to enhance chatter stability of an industrial boring bar by increasing the dynamic stiffness. A VCA actuator is used for active vibration control. The designed setup can effectively suppress undesirable vibrations in the radial direction. First, modal parameters of the boring bar are determined by experimental modal analysis. Then, the transfer function of the actuator-tool setup is identified with the sweep frequency excitation. In the following, the direct velocity feedback is successfully implemented in the vibration control loop. The results of cutting tests indicate that the actuator has a great performance in suppressing vibrations and increasing the dynamic stiffness. Hence, the developed method can significantly increase chatter stability of boring operations.