Friction analysis and modeling in metal cutting processes at elevated temperatures.

摘要

Friction is a critical factor in determining the quality of metal cutting operations. In this work, influences of workpiece material properties and the real area of contact on interfacial friction were analytically investigated at elevated temperatures. From the analytical results, the yield strength of the workpiece material was found to not only directly influence the friction as indicated by Challen and Oxley's model, but also indirectly influence the friction by changing the real contact area. An rigid plastic model for tool/workpiece real contact area was proposed which showed that the real contact area and the average asperity slope angle increased significantly at elevated temperatures. Based on experiments conducted upon a specially designed experimental apparatus, influences of tool coating material and temperature on the friction in a metal cutting process were investigated. By the help of atomic force microscopy, it was found that the friction coefficient in the metal cutting process studied was directly related to the slope of the tool asperities, the real area of contact within the tool/workpiece interface, and the level of asperity interaction. By varying the working temperature over a wide range of operating conditions, the microstructures of the workpiece materials and thermal properties of the tool coatings were found to significantly influence the friction coefficient. For the specific coating materials studied, Al2O3 was found to have the best friction and wear performance at higher temperature, while TiN performed better at the lower temperature examined. The TiC/TiN coated tools demonstrated a consistent performance with respect to friction over the range of temperature studied. Finally, an empirical model that related the friction to the yield strength of workpiece material was established and discussed.