Application of ionic liquids in interrupted minimum quantity lubrication machining of plain medium carbon steel: Effects of ionic liquid properties and cutting conditions

Minimum quantity lubrication machining has been actively researched by scientists as a viable alternative to the use of cutting fluids used in metal cutting, a source known for their operator's health and ecological concerns. MQL machining assumes significance due to the very low volumes of the lubricants used, which are often consumed in the machining processes itself. The quest for greener lubricants has lead the researchers towards vegetable oils. Ionic liquids are a relatively new family of green chemicals which have the advantage that their physical and chemical properties can be designed for specific applications. Previous work by researchers has demonstrated that ionic liquids can be used as promising lubricants in various engineering applications. This paper presents the results of a detailed study carried out to evaluate the performance of fluorine containing oil non-miscible ionic liquids and phosphonium ion based oil miscible ionic liquids, added to canola oil or polyethylene glycol in small volumes in interrupted MQL machining of a plain medium carbon steel under different cutting parameters. The result of the studies demonstrated that fluorine containing ionic liquids showed improved results at higher cutting speeds and load and could be a candidate for high speed machining applications, where the cutting zone temperatures rise above the decomposition temperatures of the ionic liquids prompting the liberation of fluorine which readily binds with the freshly produced chip under-surface and reduces the severity of the tool-chip adhesion. The phosphonium ion based ionic liquids and polyethylene glycol showed better results at lower cutting speeds where the tool-chip interface temperature stayed below the decomposition temperature of the lubricants, suggesting a strong influence of the lubricant viscosity on the cutting performance. The use of lubricants with higher viscosity resulted in improved surface roughness. The results of the study can be used as a starting guideline for the design of ionic liquids with specific chemical and physical properties for different machining applications. (C) 2018 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.