Minimum Quantity Lubrication (MQL) Using Vegetable Oil With Nano-Platelet Solid Lubricant in Milling Titanium Alloy

Improving the machinability of titanium (Ti) alloys remains unresolved for manufacturing industries because excessive tool wear and catastrophic tool failures lead to shortened tool life and low productivity with any available cutting tool system. Besides optimizing the substrate and/or coating materials for cutting tools, improving the cooling and lubricating conditions is one of the ways to improve the machinability of Ti alloys. In this paper, we explore the possibility of using a nano-platelet, lamellar-type solid lubricant of graphite Exfoliated graphite nano-platelets (xGnP^®) grade C750 (or xGnP750) in Minimum Quantity Lubrication (MQL) machining of Ti-6Al-4V (Ti64). Due to the lamellar or layered crystal structure, each layer easily slides against adjacent layers to provide the lubricity when introduced at the tool/work material interface. Although the nano-platelets have a nano-thickness, they have a micro-sized diameter, which prevents the nano-platelets from penetrating through human skin and breathing through nose. This makes the great advantage in this approach compared to other nano-enhanced MQL processes. The milling experiment shows that the nano-platelets present in the MQL oil decreased flank wear and improved the tool life compared to traditional MQL with pure oil as well as dry machining. The presence of nano-platelets reduces the micro chipping and tool fracture caused by the effect of impact in interrupted machining.