Halogen-free ionic liquid as metalworking fluids in machining: A promising cleaner approach

Metalworking fluids (MWFs) are vital in minimizing friction and wear during machining processes, improving surface quality, and reducing tool wear. With the rising sustainability concerns, demand for environmentally friendly MWFs, such as vegetable oil alternatives, has gained significant research interest worldwide. Vegetable oils have distinct physicochemical characteristics, which might affect their efficacy in lubricating applications. Apart from these merits, they possess some limitations, such as lower thermal conductivity and oxidation stability, which may impair their efficacy as MWFs. These limits may be overcome by using different MWF additives. In recent years, ionic liquids (ILs) have arisen as a new kind of MWF additive, intended to improve the lubricating properties such as thermophysical, tribological, and chemical characteristics of vegetable oils. This study compares the effectiveness of ionic liquid as additives, which includes [BMIM][BF₄]^-, [BMIM][PF₆]^-, and halogen-free [P_6,6,6,14] [i(C₈)₂PO₂]^- in pure canola oil. The research assesses the thermos-physical properties such as pH value, thermal conductivity and contact angle/wettability of the synthesized metalworking fluids. Also, it looks at critical performance variables such as cutting temperature, tool wear, and surface roughness. The findings show that a 1 % addition of [P_6,6,6,14] [i(C₈)₂PO₂]^- greatly enhances machining performance. Under [P_6,6,6,14] [i(C₈)₂PO₂]^- cutting temperatures were reduced approximately by 30 %, surface roughness was reduced by 32 $-$ 41 %, as well as SEM image showed lower tool wear at different feed rates. Further, the sustainability assessment using the pugh matrix favours the halogen-free ionic liquids [P_6,6,6,14] [i(C₈)₂PO₂]^- as metalworking fluid compared to other MWFs.