Elastic mechanics-based fixturing scheme optimization of variable stiffness structure workpieces for surface quality improvement

Abstract

The surface quality is quite important for many mechanical products. An improper fixturing scheme (i.e., magnitudes of clamping forces and fixture layout) leads to undesirable deformation of the workpiece, which will seriously affect the final quality of the machined surface, especially for the form accuracy. Current researches on fixturing scheme optimization have been mainly focused on rigid workpieces and flexible workpieces, however, seldom considered variable stiffness structure (VSS) workpieces. Besides, most existing fixturing scheme optimization models are derived based on the finite element method (FEM), which demands considerable time for computation. Therefore, there is a lack of an effective and efficient approach to improve the surface quality for VSS workpieces by fixturing scheme optimization. To this end, a novel systematic approach based on elastic mechanics is proposed in this paper. Firstly, a static cutting force model is developed to obtain the minimum clamping forces needed to maintain the fixturing stability. Secondly, by dividing the VSS workpiece into three kinds of characteristic regions, the analytical solutions of the elastic deformation induced by clamping forces are derived using elasticity theory. Thirdly, the optimization model is solved by the genetic algorithm, so as to minimize the maximum fixturing induced deformation of the surface to be machined. The effectiveness and efficiency of the proposed approach are verified by a face milling experiment on a four-cylinder engine block, and the final quality of the machined surface is improved by 9.1%.