Modeling of an Active Boring Bar

Vibration problems occurring during internal turning operations in the manufacturing industry urge for adequate passive and/or active control techniques in order to increase the productivity of machine tools. Usually, passive solutions are based on either boring bars made partly in high Young's modulus non-ductile materials such as intered tungsten carbide or boring bars with tuned vibration absorbers adjusted to increase the dynamic stiffness in the frequency range of a certain resonance frequency of the boring bar. By utilizing an active boring bar with an embedded piezoceramic actuator and a suitable controller, the primary boring bar vibrations originating from the material deformation process may be suppressed with actuator-induced secondary "anti-" vibrations. In order to design an active boring bar, several issues have to be addressed, i.e., selecting the characteristics of the actuator, the actuator size, the position of the actuator in the boring bar, etc. This usually implies the manufacturing and testing of several prototypes of an active boring bar, and this is a time-consuming and costly procedure. Therefore, mathematical models of active boring bars incorporating the piezo-electric effect that enable the accurate prediction of their dynamic properties and responses are of great importance. This report addresses the development of a "3-D" finite element model of the system "boring bar-actuator-clamping house". The spatial dynamic properties of the active boring bar, i.e., its natural frequencies and mode shapes, as well as the transfer function between actuator voltage and boring bar acceleration are calculated based on the "3-D" FE model and compared to the corresponding experimentally obtained estimates. Two types of approximations of the Coulomb friction force, the arctangent and the bilinear models, are evaluated concerning modeling contact between the surface of the boring bar and the clamping house