TRACKING WORKPIECE STABILITY UNDER VARYING CUTTER POSITIONS, MASS AND COMPLIANCE OF WORKPIECE IN POCKET MILLING

Abstract

Manufacturing accuracy and surface finish as well as productivity by way of high metal removal rates are mainly restricted by the occurrence of workpiece vibrations and loss of stability. In this paper, dynamic stability of Al-6061-T6 prismatic workpiece located in a milling fixture with 3-2-1 location principle and two hydraulically operated clamps is investigated under spatially varying cutter position and continuously decreasing mass and compliance of a workpiece during pocket milling operation. The mathematical model for the fixtureworkpiece system is based on Hertzian contact theory. The workpiece and fixture elements are considered rigid and the model takes into account the only contact stiffness. A six-dof dynamical model, that includes metal removal effect (MRE), is developed to simulate the dynamical response of the fixture workpiece system in MATLAB Simulink. Finally, the lift-off and macro-slip is calculated and the stability is determined for each contact. The effect of metal removal on the workpiece during machining is considered for 20% and 50% metal removal. For increased metal removal the measured and simulated accelerations are compared and found to have a good agreement with each other. The theoretical model thus developed for dynamic response simulation will be integrated with a Computer Aided Fixture Design (CAFD) system.