Investigation of friction in end-milling of Ti-6Al-4V under different green cutting conditions

The friction in end-milling of Ti-6Al-4V has a great effect on tool life and surface quality of workpiece. This paper focuses on the effects of minimum quantity lubrication (MQL) with high pressure air and dry cutting (without coolant) in performance, in terms of friction reduction, cutting force, and cutting temperature. The equivalent friction pressure coefficient method has been proposed to analyze the friction in this study. Comparative experiments were performed to investigate friction in milling titanium alloy (Ti-6Al-4V) under different cooling/lubrication conditions (dry, MQL, and high pressure air). The main results were as follows: (1) Compared with dry cutting, the application of MQL or high pressure air lead to drastic reduction in friction at lower cutting speed in end-milling of Ti-6Al-4V. Furthermore, MQL and high pressure air had similar performance in reducing friction. (2) At higher cutting speed, the cutting performances of three coolant supply strategies were slightly different. But, the efficiency of application of MQL and high pressure air in the high-speed cutting condition was not yet obvious. Moreover, it was shown that MQL can reduce the friction at the chip-tool interface when cutting parameters and matching parameters of MQL were chosen properly. Therefore, it appears that MQL and high pressure air can be alternative environment friendliness approaches to improve machinability of difficult-to-cut materials.