Development of a New Dynamic Friction Model for Analytical Modeling of Elliptical Vibration Assisted Turning Process

A new dynamic friction model for modeling of elliptical vibration assisted turning (EVAT) was developed in this research. The periodic change of the friction force direction is known to be one of the most important causes of this phenomenon. In modeling of machining processes (including the EVAT process), static Coulomb friction model was employed by most of the researchers. Because of the periodic change in the friction force direction during the elliptical vibration path, the simple Coulomb friction model could not reflect the dynamic friction phenomena between the chip and the tool such as stick-slip and dynamic breakaway. In this research the LuGre dynamic friction model, which had been successfully employed for modeling of EVAT process, was modified in compliance to the machining process. To modify the LuGre model, the LuGre model coefficients were modified so that the effect of the temperature change of the contacting surfaces (which plays a key role in the friction behavior between the chip and the tool) could be reflected by the model. To determine the coefficients, orthogonal machining tests were performed and the Genetic Algorithm optimization method was carried out to derive the coefficients. Afterward, the results achieved from both dynamic models were compared with experimental results and Coulomb model results. The results from the new modified LuGre model were in better agreements with the experimental results.