## 4 Nanofluid Application in Machining
Adding the graphene nanoplatelets to the Al\({}_{2}\)O\({}_{3}\) nanofluid increased the tribological characteristics. Figure 2 illustrates the mechanism of nanoparticles entrapped between the sliding surfaces. Recently, the MQL system was adopted for the application of a developed nano lubrication system to the cutting zone. Less nanolubricant consumption is a beneficial aspect of using pressurized air to accelerate the addition of nanolubricant into the tool/workpiece interface. Using nanolubricant in the milling process helped achieve high-quality machined surfaces due to the presence of applied nanoparticles. [PERSON] et al. [80] examined the impact of the MoS\({}_{2}\)-based nanolubrication system on the machined surface morphology using the MQL system. These authors verified that a developed MoS\({}_{2}\)-based nano lubrication system is beneficial for accomplishing high surface quality. [PERSON] et al. [81] investigated the key machining characteristics during the milling process of Ti-6 Al-4V accompanied by applying a hybrid nanofluid (Al\({}_{2}\)O\({}_{3}\)-MWCNT). The authors proved that using hybrid nanofluid leads to attaining better performance related to tool wear that results in a reduction of energy consumption. A successful drilling process is frequently determined by the efficiency of the employed drilling fluid. Drilling fluids can control surface pressure, prevent contamination, and function as lubrication [82]. [PERSON] et al. [83] created a novel nanofluid/ MQL technology for microdrilling. They showed that the created nanofluid/MQL with a loading concentration of 2 wt.% could achieve an attractive microdrilling force and microdrilling torque, as well as increase drilling quality due to a substantial decrease in the drilling process. The grinding process is important in materials removal operations, particularly if it is required to reach close tolerances. Formulated novel  
Figure 2: Synergic influence of the Al\({}_{2}\)O\({}_{3}\) and Al\({}_{2}\)O\({}_{3}\)–graphene nanoplatelets trapped between the sliding surfaces. Reprinted with permission from Ref. [79]. 2018 Elsevier. nanofluids can substitute traditional cutting fluids to increase the quality of the grinding process, lubrication, and surface finish. [PERSON] et al. [84] formulated and used a novel ND-based nanofluid associated with the MQL technique in the grinding process. They reported a considerable decline of 33.2% in normal components, while the developed reduction in tangential components was reported as 30.3%. The surface roughness measurement resulted in a considerable decrease of 64% due to the presence of used nanoparticles. In a machining process, four main characteristics must be controlled: surface roughness, cutting force, tool wear, and tool life in which the nanofluids could have an important role [68]. Required surface quality is one of the key factors in the machining process. This surface quality can be evaluated by the surface roughness, which is a technical requirement for most mechanical products [85]. The utilization of nanofluids as a substitution of conventional cutting fluids has improved the quality of products by decreasing their surface roughness. So, the reduction of surface roughness could go from 8.72% using Al\({}_{2}\)O\({}_{3}\) with carbon nanotube (CNT) in vegetable oil [86] to 47.8% with aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) with vegetable oil [87]. The cutting force is a very important parameter directly related to the cost-effectiveness of parts, so high-level cutting force demands raised values of power consumption and, consequently, the machining costs increasing. Some research works showed a significant decrease in cutting forces when nanofluids are used. This diminution can contain up to 50% aluminum oxide added to the conventional cutting fluid [88]. However, opting for a more environmentally friendly choice, it is also possible to reduce 37% in cutting forces by applying coconut oil (CC) associated with nano molybdenum disulfide (nMoS\({}_{2}\)) [89].