OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 4 2024 a b c d Fig. 4. Viscosity (a); thermal conductivity (b); specifi c heat (c); coeffi cient of friction (d) Under continuous cutting conditions, an electric dynamometer with a piezo sensor mounted on the lathe measured the cutting forces in real time. The measured cutting forces are shown in Fig. 5, a for various lubrication conditions. Consistently low particle concentrations reduce all forces, while higher concentrations increase it only slightly. As the concentration of nanoparticles increases, a dense or slurry layer is formed, which increases the cutting force. At a CuO/Al2O3 content of 1.6 wt. %, the cutting force decreases by 32 %. This is due to the formation of an adhesive coating between the sliding surfaces due to the layered nanoscale structure of Al2O3, which also makes the metal surfaces more easily absorbable. This can be seen from the friction coeffi cient in Fig. 4, d. CuO/Al2O3 HCF also has a higher viscosity than the base fl uid. The thick fi lm that forms during cutting eventually reduces the cutting pressure on the contacting surfaces. The cutting temperature can be aff ected by the heat generated at the chip-tool interface. A digital pyrometer was used to determine the temperature of CuO/ Al2O3 HCF. Fig. 5, b shows diff erent lubrication conditions aff ecting the cutting temperature. The cutting temperature was signifi cantly reduced by using the CuO/Al2O3 hybrid nanofl uid. The reduction in cutting temperature can be achieved when the copper and aluminum oxide concentration is as low as 2.4 %. Compared with other concentrations, the sample containing 1.6 wt. % CuO/Al2O3 has the lowest cutting temperature (67 °C). The hybrid nano cutting fl uid containing 1.6 wt. % CuO/Al2O3 reduces the cutting temperature by 43.4 % compared with the traditional cutting fl uid. By using this HCF, the thermal conductivity and heat transfer coeffi cient of the CuO/Al2O3 nano cutting fl uid can be improved to reduce the temperature in the cutting zone. The eff ectiveness of cutting fl uids is determined by its ability to reduce the surface roughness of the workpiece. Fig. 5, c shows the measured surface roughness. With an increase in the concentration of
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