Environmental Friendly Milling of Inconel 718: Dry, Air cooled and Bio-Based Minimum Quantity Lubrication Machining
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Date
2026-01-07
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Department of Mechanical Engineering, NITS
Abstract
Sustainable 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.