IDENTIFICATION OF SPATIAL DYNAMIC PROPERTIES OF THE BORING BAR BY MEANS OF FINITE ELEMENT MODEL: COMPARISON WITH EXPERIMENTAL MODAL ANALYSIS AND EULER-BERNOULLI MODEL

摘要

In metal cutting the boring operation is known to be one of the most troublesome regarding vibration. Boring bars are frequently subjected to vibrations originated from the load applied by the workpiece material deformation process. These vibrations are easily excited due to the boring bars general geometric dimensions, i.e. large length to diameter ratio. Large overhang is usually required to perform internal boring operation and as a consequence the vibration may frequently reach extremely high levels, which result in a poor surface finish, reduced tool life and annoying noise level in the working environment. The vibration problem is directly related to the first bending modes of a boring bar. Therefore investigations of the boring bar's spatial dynamic properties are of a great importance. The results from experimental modal analysis show that a conventional analytical approach - calculation of boring bar eigenfrequencies using an Euler-Bernoulli model - results in rough estimates. This can be explained by existing nonlinearities introduced e.g. in the areas of contact between the boring bar and the clamping bolts as well as the clamping house, which is not considered in the analytical model where the boring bar instead is assumed to be rigidly clamped. Therefore the estimation of the eigenfrequencies and eigenmodes of a boring bar based on a 3-D finite element model of the clamped boring bar incorporating contact between the bar and the bolts respective the clamping house is a more beneficial strategy. This paper addresses the estimation of the boring bar's first eigenfrequencies and corresponding eigenmodes based on the 3-D finite element model. The results are compared with results obtained both from experimental modal analysis and an analytical Euler-Bernoulli model.