Experimental evaluation on tribological performance of the wheel/workpiece interface in minimum quantity lubrication grinding with different concentrations of Al2O3 nanofluids

Lubricants play a critical role in machining, especially in the grinding process. As a result of the growing need for environmental protection and the increasing number of health problems faced by workers, traditional lubricants are gradually being replaced. Nanofluids, which contain nanoparticles in the proper base fluid, can serve as a low-carbon, “green” lubricant. As a lubricant, nanofluids show improved heat transfer capability and lubricating properties. Friction between abrasive grains and workpieces during grinding can directly influence grinding force, grinding wheel wear, and workpiece quality. Therefore, increasing lubricating effects is an effective way to improve machining performance. In this study, a nanofluid, as the lubricating fluid, is developed by adding 0.5 vol% to 4.0 vol% Al2O3 nanoparticles to palm oil for the surface grinding of a Ni-based alloy in minimum quantity lubrication (MQL) mode. The tribological performance at the grinding wheel/workpiece interface under different concentrations of nanoparticles is studied on the basis of macroparameters (force ratio, specific energy, and G-ratio) and microparameters (surface quality, microstructure of abrasive grains and grinding debris, viscosity, and contact angle). Results show that the nanofluid flows through the grinding wheel and workpiece interface and forms a lubricating oil film that reduces friction significantly. An optimum concentration of nanoparticles is also achieved. The smallest force ratio of 0.281 is obtained when the volume concentration of the nanoparticles is 1.5%, whereas the minimum roughness of Ra = 0.301 μm, slender grinding debris, and maximum drop wetting area are realized when the volume concentration is 2.0%. Hence, the nanofluid exhibits excellent overall tribological performance. In addition, a nonlinear relationship exists between the lubricating effect and the concentration of the nanofluid. The appropriate concentration of Al2O3 in the nanofluid thus provides good tribological performance and have both environmental and economic benefits for industrial applications.