Abstract
Nanofluid is the suspension formed by lubricating oil and nanoparticles with particles sizes of 1~100 nm, and common nanoparticles include metal nanoparticles (Cu, Ag, etc.), oxide nanoparticles (Al2O3, SiO2, ZrO2, etc.), carbides (CNT, diamond), and MoS2 nanoparticles, etc. Different nanoparticles exhibit various physicochemical properties (e.g., structure and shape), which can influence their tribological characteristics. In this work, six nanofluids, namely, MoS2, SiO2, diamond, carbon nanotubes (CNTs), Al2O3, and ZrO2, were used as minimum quantity lubrication grinding fluids to select the kind of nanoparticles with optimum lubrication performance in grinding nickel alloy GH4169. Experimental results concluded the following: 1) Nanoparticles with spherical or sphere-like molecular structure and nanofluids with high viscosity demonstrate superior lubrication performances. 2) The polishing effect of nanodiamond particles enhances their surface morphology. 3) The lubricating property of the six nanofluids is described in the following order: ZrO2 < CNTs < ND < MoS2 < SiO2 < Al2O3.
Top12.1 Introduction
Grinding is widely used in machining and the process is a random integration of sliding, ploughing, and cutting by abundant irregular abrasive grains scattered on a grinding wheel/workpiece interface viewed from microstructure (Malkin & Guo, 1991). The abovementioned process exerts higher units of grinding force and grinding speed than other machining processes, thus utilizing significantly higher grinding energies. In particular, hard materials in the grinding process will generate a lot of additional heat (Ding et al., 2015). Flood technology is the most common cooling–lubrication method used to improve the machining quality of workpieces and cutters. However, the surface processing quality of workpieces is not satisfactory because the grinding wheel at high-speed forms a layer of gas-barrier, which makes entry into the grinding wheel and workpiece interface difficult for numerous grinding fluids (Li, Wang, & Zhang, 2013). Minimum quantity lubrication (MQL) technique is a green processing method (Baheti, & Guo, 1998). The MQL technology uses a minimum quantity of lubricants to achieve satisfying lubrication performance. This technique mixes a minimum quantity of lubricants in high-pressure gases, which can break through the air-barrier layer of the grinding wheel and arrive at the grinding area after mixing atomization. In particular, high-pressure gas plays a role in cooling and debris removal. Li et al. (Li, Hou, Xiu, & Cai, 2008) performed experiments to evaluate the performance of MQL technology compared with that of conventional flood cooling. Mao et al. (Mao et al., 2013) analyzed the heat-transfer coefficient on workpiece surface during MQL grinding and concluded that the theory of surface heat-transfer coefficient during MQL grinding is creditable. Numerous studies and experiments have indicated that the grinding process is improved by MQL technology. More importantly, the dosage of the grinding fluid significantly decreases, thereby reducing hazards to workers and the environment (Zhang, Li, Jia, Zhang& Zhang, 2015).