Different parameters (air pressure, quantity of minimum quantity lubrication (MQL) oil, position of nozzle, etc.) of an MQL system have different effects on the milling force and milling temperature. The cutting force and cutting temperature, which are closely related to lubrication and coolant, play significant roles in improving/reducing the cutting quality of a workpiece and extending/shortening the tool life. The present work investigates experimentally the effects of different MQL parameters (air pressure, quantity of oil consumed, and position of the nozzle) in end-milling titanium alloy (Ti–6Al–4V). The experimental results show that the penetrating ability of MQL oil mist has a significant effect on the milling forces and milling temperatures. When the values of air pressure and spraying distance were either too large or too small, it is not good for oil mist to penetrate into the contact zones. The spraying angle of the nozzle position has a minimal impact on the penetration ability. Conversely, the amount of oil delivery is the most important part of MQL application. The minimum quantity of oil consumption can be obtained. The results will help to select optimum MQL parameters in end-milling titanium alloy.

Minimum quantity lubrication is an alternative to realize machining titanium alloys both economically and ecologically. In order to apply minimum quantity lubrication more efficiently, an investigate of the effects of the operating parameters involving oil supply, compressed air supply, and nozzle orientation is required. This article focuses on the oil supply rate of minimum quantity lubrication and aims to identify the effects of the minimum quantity lubrication applications with different oil supply rates in high-speed end milling of Ti–6Al–4V. The experiments were conducted by adjusting the oil supply rate from 2 ml/h to 14 ml/h, and cutting force, surface roughness, tool wear and failure mode, and tool wear mechanism were discussed. The results indicate that the increase of the oil supply rate effectively reduces cutting force and surface roughness, but after 10 ml/h the reduction is no longer significant. Increasing oil supply has growing penetration depth along the cutting edge, and by increasing the oil supply rate the length of the chipping edge can be notably reduced. For an insufficient oil supply rate (2 ml/h∼10 ml/h) chipping on the cutting edge introduced by diffusion wear is the main tool rejection reason, but at 14 ml/h no diffusion wear is found and the uniform flank wear is dominant, owing to reduced cutting temperature.