Finite element model updating of boring bar and determination of chatter stability

Abstract

The use of Finite-Element Models (FEM) has become common practice in structural analysis and design. Commercial Finite element package allows designers to create, simulate, and analyze real-time problems. However, these models often do not represent the actual physical characteristics of the structure. Many factors affect the accuracy of the numerical model; these include simplified assumptions regarding the boundary conditions, unplanned loads on the structure, improper modeling joints, and material imperfections. Interest in the vibration properties arises because nearly all structures are subject to the vibration of one form or another, which is usually undesirable. In machine tools, boring bars are slender and cantilevered, hence they generally vibrate with large amplitudes under the action of cutting forces which result in machining instabilities, i.e. chatter. In this paper, the Iterative inverse Eigen sensitivity updating method is used to update the finite element (FE) model of a boring bar, using experimental modal data. The finite element model of the cantilevered boring bar is modeled using Euler-Bernoulli beam elements. The degree of correlation between the FE model and the experimental model is ascertained by determining the difference in natural frequencies and by using Modal Assurance Criterion (MAC). Suitable updating parameters are chosen and these parameters are iteratively updated using Inverse Eigen sensitivity method to match the dynamic responses of the FE model to that of the experimental model, and the modal parameters of the updated FE model are compared with the experimental model. Better correlation values indicate the enhanced similarities between experimental and analytical models. The updated model is used to obtain tool tip receptance and determine chatter stability. The updated FE model yields improved accuracy in chatter stability estimations.