*3.3. Characteristics of Vegetable Oil-Based MWFs in Machining Applications*

It has been shown that vegetable oil-based MWFs have shown superior cooling and lubrication properties compared with mineral oil-based MWFs. This is mainly because of the fact that the presence of saturated fatty acids in vegetable oil aid the formation of the lubricant layer at the work–tool interface, and the structure of the triglycerides provides the desired lubrication characteristics [65]. In a study by Sani et al. [66], it was shown that by using modified jatropha oil with ionic liquid, the cutting energy was reduced. Ionic liquids consist of acidic ionic liquids (AIL) and protic ionic liquids (PIL). The authors also reported that better results were obtained when the mixture consisted of 10% AIL with jatropha oil and 1% PIL with jatropha oil. They highlighted that the specific cutting energy was reduced around 4 to 5%, the cutting temperatures were reduced by 7 to 10%, the friction coefficient was reduced by 2 to 3%, and the tool–cup contact's length was reduced by 8 to 11% when the results were compared with the reference mineral oil-based MWF. Their results are also shown in graph form in Figure 6.

**Figure 6.** The variation of the specific cutting energy with respect to the mixture of modified jatropha oil (MJO) and AIL/PIL [66].

Vamsi Krishna et al. [67] showed in their research that better surface quality was obtained when using nano-boric acid in coconut oil compared with the surface quality obtained from the industrial lubricant SAE 40, and their results are shown in Figure 7. It can be seen from the figure that the coconut-based oil resulted in lower values of surface roughness while also changing the cutting speed.

**Figure 7.** The variation of the surface roughness with the cutting speed [67].
