Evaluation of ionic liquids as lubricants in micro milling – process capability and sustainability

Ionic liquid has gained much attention from the research community, due to its eco-friendly properties, including low vapor pressure, non-flammability, thermal stability, and high-friction reduction abilities. In this study, a series of experiments were performed to investigate the characteristics of ionic liquids as lubricants in micro end milling, especially the sustainable characteristics. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][TFSI]), a low-viscosity ionic liquid, and 1-butyl-3-methylimidazolium iodide ([BMIM][I]), a high-viscosity ionic liquid, were examined and compared with two conventional oils and distilled water. Dry machining was used as a reference case for the testing. The workpiece material is aluminum Al 5052, while tool bit is made of tungsten carbide (WC) with diameter of 200 μm. The performance of each liquid as lubricant was considered through machining data as cutting forces, surface morphology and surface roughness of machined workpiece; and the sustainability was considered through the evaporation rate during machining. Analysis of data showed that micro end milling with ionic liquids, and in particular the high-viscosity lubricant ([BMIM][I]), provided a slightly better machined surface and exhibited extremely low volatility compared with conventional oils or other lubrication conditions.