Experimental evaluation of coolant-lubricant properties of nanofluids in ultrasonic assistant MQL grinding

Abstract

Despite many advantages of MQL grinding in technological, environmental, and economic eras, it still has a severe thermal deficiency. In this paper, two approaches for decreasing this drawback are utilized: (1) the addition of nanoparticles to MQL fluid and (2) the combination with ultrasonic vibration. Therefore, at the first step, six different water-based nanofluids from two different properties class were investigated. The nanoparticles including TiO2, SiO2, and Al2O3 have effective lubrication properties; and nanoparticles including CuO, NiO, and MWCNTs have effective cooling properties. Output parameters are considered to be force ratio, tangential grinding force, grinding temperature, and also surface quality. Grinding temperature was recorded by a high-speed infrared camera. All the results show effectiveness of in improving performance of MQL grinding. According to the results, in different specific removal rates, the Al2O3 nanofluids have the highest lubrication effect in comparison to other nanofluids. It can reduce average of force ratio roughly by 16.2%. Furthermore, similar results are obtained in case of tangential grinding force and grinding temperature (F t and T: NiO > CuO > TiO2 > MWCNTs > SiO2 > Al2O3). On the other hand, using the Al2O3 nanofluid in the MQL process leads to a decrease in the same parameters by 31.2 and 28.9%, respectively. Generally, the results show that “lubricant nanoparticles” (especially Al2O3) show a better performance than “coolant nanoparticles.” At the next step, in order to further improve grinding performance, Al2O3 nanofluid MQL was combined with ultrasonic-assisted grinding. The results show that force ratio and tangential grinding force decrease by an average of 20 and 42.6%, respectively. Also it leads to a decline in grinding temperature up to 48% (from 254 to 132 °C) in comparison to dry grinding. Therefore, shiny surfaces without any thermal damage were obtained rather than the dark and burned surface in dry grinding. Morphology of ground surface obtained by optical microscope with ×1000 magnification shows that combination of Al2O3 nanofluid MQL with UAG has fewer defects, especially no plastic deformation and side flow, which are due to effective lubrication. Furthermore, the shape, type, and size of the generated chips are similar to those in conventional fluid grinding rather than dry grinding that indicates similar cutting mechanism.