Ultrasonic-assisted turning is a machining process in which a vibrational displacement (usually in ultrasonic frequencies) is superimposed with the machining displacements in the cutting direction (one-dimensional ultrasonic-assisted turning) or in the cutting direction along with the radial direction (two-dimensional ultrasonic-assisted turning or elliptical ultrasonic-assisted turning). In this research, an elliptical ultrasonic-assisted turning tool is designed in ABAQUS software, in which the longitudinal and bending vibration modes have the minimum resonance frequency difference, so that the resonance of both the vibration modes can be achieved in a definite frequency. A set of half-ring piezoelectric stacks is employed for excitement of the bending mode, and a set of ring-shaped piezoelectric stacks is used for the excitement of the longitudinal mode. There is a phase shift with the amount of p/2 between the longitudinal and bending vibration modes to produce an elliptical vibration. The manufactured tool is employed for machining of copper, which resulted in better surface finish and lower cutting forces.
A novel analytical model for prediction of forces in elliptical vibration-assisted turning using a dynamic friction model is presented in this article and verified with experimental elliptical vibration-assisted turning tests. In elliptical vibration-assisted turning process, the main cause of force reduction is the reversal of the friction force direction in a fraction of vibration cycle time. In analytical modeling of elliptical vibration-assisted turning, the change of the relative sliding velocity direction causes a stick–slip condition which cannot be detected with static friction models like Coulomb model. In this research, a dynamic friction model, named LuGre model, is used to predict the machining forces in elliptical vibration-assisted turning. To derive the model coefficients, a series of orthogonal cutting experiments are performed on Al 6061, Al 7075 T6, Copper and Inconel 718, and the friction coefficients are identified using genetic algorithm optimization method. The cutting forces are determined by incorporating the friction forces calculated from LuGre model. To verify the results, a series of elliptical vibration-assisted turning experiments are performed on four above-mentioned workpiece materials using an elliptical vibration-assisted turning tool. The machining forces are then compared with the analytical results. The results achieved from the analytical solution using LuGre dynamic friction model are in a good agreement with experimental results.
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