Dynamic Analysis and Modeling of Machine Tool Parts

Abstract: Boring bar vibration during internal turning operations in machine tools is a pronounced problem in the manufacturing industry. Vibration may easily be induced by the workpiece’s material deformation process, due to the bar’s normally slender geometry. In order to overcome the vibration problem in internal turning active or/and passive control methods may be utilized. The level of success achieved by implementing such methods is directly dependent on the engineer’s knowledge of the dynamic properties of the system to be controlled. This thesis focuses predominantly on three steps in the development of an accurate model of an active boring bar. The first part considers the problem of building an accurate ”3-D” FE model of a standard boring bar used in industry. The influence of the FE model’s mesh density on the accuracy of the estimated spatial dynamic properties is addressed. With respect to the boring bar’s natural frequencies, the FE modeling also considers mass loading effects introduced by accelerometers attached to the boring bar. Experimental modal analysis results from the actual boring bar are used as a reference. The second part discusses analytical and experimental methods for modeling the dynamic properties of a boring bar clamped in a machine tool. For this purpose, Euler-Bernoulli and Timoshenko distributedparameter system models are used to describe the dynamics of the boring bar. Also, ”1-D” FE models with Euler-Bernoulli and Timoshenko beam elements have been developed in accordance with distributedparameter system models. A more complete ”3-D” FE model of the system ”boring bar - clamping house” has also been developed. Spatial dynamic properties of these models are discussed and compared with adequate experimental modal analysis results from the actual boring bar clamped in the machine tool. This section also investigates sensitivity of the spatial dynamic properties of the derived boring bar models to variation in the structural parameters’ values. The final part focuses on the development of a ”3-D” FE model of the system ”boring bar - actuator - clamping house”, with the purpose of simplifying the design procedure of an active boring bar. A linear model is addressed along with a model enabling variable contact between the clamping house and the boring bar with and without Coulomb friction in the contact surfaces. Based on these FE models’ fundamental bending modes, eigenfrequencies and mode shapes, control path frequency response functions are discussed in conjunction with the corresponding quantities estimated for the actual active boring bar.