ABSTRACT
Contact deformations and structural deformations are inherent in a fixture-workpiece system, resulting in dimensional and form inaccuracies in machined components. During metal removal, the mass and compliance of the workpiece vary in different proportions depending on the volume and geometry of metal removal. This leads to a gradual increase in workpiece deformations and a shift in the natural frequencies (ωn) from that of the initial unmachined workpiece. This causes a change in dynamic magnification factor (transmissibility) and vibration amplitudes. Thus, as machining progresses, the undesirable workpiece deformations and inaccuracies creep in, particularly in solid workpieces involving substantial metal removal and thin-walled workpieces. Accurate identification of changing dynamic behavior in the workpiece and control of these vibrations can maintain machining quality and productivity. In this work, we have developed a fully numerical approach to track and quantify the frequency shift and counter its effect by tweaking the clamping and cutting forces of the fixture-workpiece assembly. To validate the numerically obtained values of natural frequencies, experiments are performed on an electrodynamic shaker at different stages of pocket milling and for various clamping pressures. The natural frequencies obtained numerically show good agreement with experimental values, with a maximum error of ±10%. Subsequently, the effect of metal removal on workpiece vibrations is presented for different pocket geometries and clamping pressures. Finally, to control increasing vibrations due to decreasing workpiece stiffness, a compensation scheme is presented based on the manipulation of clamping pressures.
