**4. Conclusions**

length compared to the surface lubricated with SE. It was clearly seen that the various types of the metalworking fluids clearly affected the tool-chip contact length. The poor lubrication effect of the SE has resulted in the high frictional sticking contact with the workpiece material and produces high shear and strain stress on the cutting edge, which leads to the high

The lubricant forms an intrinsically hydraulic wedge between the chip and the rake face of the tool insert, which may prevent seizure between the tool-chip interfaces and thus greatly lower the cutting force [48]. The addition of additives has successfully reduced the total stresses on the sticking and sliding regions during the chip formation processes [26, 36]. The tribofilm formed on the sliding surfaces acts as a wear-protected film and the lubricant spray mist penetrates to the tool cutting edge. It reduces the friction stress and subsequently shortens the tool/chip contact length and improved chip control [43, 48]. Sticking or seizure occurs at the tool edge interface and the chip then slides beyond the sticking region. The occurrence of material transfer or adhesion on the rake face indicates the material wear mechanism and the lubrication effects of different lubricant samples during the material removal process. The

**Figure 9.** Optical and SEM images of the selected surface morphology on the cutting tools rake face at 50×, 75×, and 200×

magnifications respectively; (a, a', a") SE; (b, b', b") MJO + PIL1% and (c, c', c") MRPO + hBN0.05.

frictional stress and longer contact length [39, 49].

58 Lubrication - Tribology, Lubricants and Additives

surface topography of the sliding region is presented in **Figure 9**.

From the experimental data analyzed in this work, the following conclusions are obtained:

