Effects of continuous minimum quantity lubrication with ultrasonic vibration in turning of titanium alloy

Minimum quantity lubrication (MQL) technique has been widely used in different machining processes. However, oil mist discharged from MQL system induces negative effects for working space. In this paper, a continuous MQL system with ultrasonic vibration (U-CMQL) is proposed for near dry machining process. A valve-less micro-pump is designed to supply continuous lubrication to the cutting edge without making oil mist. Penetration mechanism of micro lubrication in ultrasonically assisted machining (UAM) process is firstly analyzed. Experiments are carried out to study the influence of dry machining, ultrasonically assisted machining, and U-CMQL machining on turning performance of Ti-6Al-4V alloy. Cutting force, tool wear, surface roughness, and chip morphology are experimentally analyzed. The results show that U-CMQL technique not only maintains neat working area but also improves the machinability characteristics to some extent. In comparison with dry machining and ultrasonically assisted machining, U-CMQL shows lower cutting force and tool wear rate due to the combined advantages of lubrication and vibration. Moreover, short tool-chip contact length, favorable chip morphology, and better surface integrity are obtained under U-CMQL machining.