Sharma, Deepak Kumar2026-10-072026-10-072026-01-07http://nits.ndl.gov.in/handle/123456789/162Sustainable manufacturing has become increasingly important due to the environmental and health risks associated with mineral-based cutting fluids. As a safer alternative, bio-based lubricants especially those from vegetable oils are gaining attention because they are biodegradable, renewable, and naturally lubricating. This research focuses on the development, analysis, and use of nanoemulsions based on Putranjiva roxburghii oil for the eco-friendly and efficient milling of Inconel 718, a hard-to-machine nickel-based superalloy widely used in aerospace, marine, and high-temperature applications. The Putranjiva roxburghii seeds, available in certain regions, were processed using a traditional oil extraction method to obtain the base oil. Known for its good tribological performance, this non-edible oil was selected as a sustainable base fluid. To improve its heat, transfer and lubrication characteristics, two nanoparticles silicon dioxide (SiO2) and graphene were added in different weight percentages (0.25%, 0.5%, 0.75%, and 1%). Additionally, hybrid nanoemulsions were created using equal parts of SiO2 and graphene. Emulsions with varying water-to-oil ratios (from 100:5 to 100:30) were also prepared to find the best composition for Minimum Quantity Lubrication (MQL) use. A range of characterization techniques was applied to analyze the nanoparticles’ size, shape, and distribution, along with the thermal, rheological, and surface properties of the nanoemulsions. Results showed that adding nanoparticles significantly improved thermal conductivity, specific heat, and wettability compared to the base oil. The 0.75 wt.% graphene nanofluid showed the highest thermal conductivity, while the hybrid nanofluid (0.5 wt.% each of SiO2 and graphene) demonstrated the best wettability on Inconel 718. These findings suggest that no single nanofluid composition is perfect for every application, highlighting the need for multi-objective optimization based on machining requirements. The performance of these nanoemulsions was tested through face milling experiments on Inconel 718 under dry, air-cooled, and MQL conditions using cemented carbide cutting tools. Machining parameters like spindle speed, feed rate, and depth of cut were varied, and Box’s evolutionary optimization method was used to find the best settings. The nanoemulsions, delivered through an MQL system, were evaluated against performance indicators such as surface roughness, tool and workpiece temperatures, tool wear, cutting force, torque, and power consumption. The findings clearly showed that Putranjiva roxburghii oil-based nanoemulsions performed better under MQL conditions. The hybrid nanofluid in particular provided excellent cooling and lubrication of the combined benefits of wear resistance of SiO2 and high thermal conductivity and lubricity of graphene nanoparticles. This formulation achieved a minimum surface roughness of 0.29 µm 54.7% better than dry machining and 46.3% better than air cooling. The lowest recorded tool and workpiece temperatures were 41.1 °C and 31.46 °C, respectively, at 180 rpm spindle speed, 16 mm/min feed rate, and a 100:20 emulsion ratio. Microscopic inspection showed that tool wear was much lower under MQL, especially with the hybrid nanoemulsion, which showed minimal abrasive and crater wear. In contrast, dry machining resulted in noticeable abrasive wear and built up edge formation. MQL also led to more consistent cutting forces, reduced torque and power consumption, and longer tool life. However, improper dispersion or agglomeration of nanoparticles especially in hybrid mixtures could reduce surface quality and thermal stability. This emphasizes the need for stable and uniform nanoparticle dispersion for effective application. This study showed that nanoemulsions made from Putranjiva roxburghii oil, especially the hybrid type, are a promising and eco friendly alternative to traditional cutting fluids. Their better heat transfers and lubrication improved machining results. Future research can work on improving nanoparticle stability and studying the environmental impact and biodegradability of these fluids.en