Application of Nanofluid Composite Electrostatic Spraying in Machining of Aluminum Alloy: Effects of External/Internal Fluids

Nanofluid composite electrostatic spraying (NCES) is a novel minimum quantity lubrication (MQL) technology which employs electricity to atomize external fluids (oil or oil-based nanofluids) and internal fluids (water or water-based nanofluids) into composite droplets. Its performances largely depend on its external/internal fluids. Therefore, selecting proper external/internal fluid is critical for achieving optimal results with this technology. This paper investigated the machining characteristics of aluminum alloy milling assisted by NCES using various external/internal fluids. In this research, commercial vegetable-based lubricant and graphite, graphene, and carbon nanotube (CNT) oil-based nanofluids were utilized as the external fluids, and water and graphite, CNT, and graphene oxide (GO) water-based nanofluids were utilized as the internal fluids, so as to form 16 kinds of external/internal fluids. The charging, electro-wetting, and frictional tests were tested to analyze the impacts of external/internal fluids in the NCES assisted machining of aluminum alloys. The findings suggested that owing to the excellent charging and electro-wetting properties, as well as the superior lubrication effects of appropriate amount of graphite, the NCES using commercial vegetable-based lubricant/graphite water-based nanofluid showed the best lubrication performance and the best comprehensive effect of cutting force and temperature reduction, particularly at an external/internal fluid flow rate of 10/5 ml/h. Compared with other external/internal fluids, the NCES using commercial vegetable-based lubricant/graphite water-based nanofluid provided 7.87–27.55% reduction in cutting force and 0.87–9.16% reduction in cutting temperature.