Sustainability-Oriented Evaluation of Carbon Nanofluid-Based Minimum Quantity Lubrication: Machining Performance and Resource-Efficiency Implications

Abstract

Sustainable machining requires lubrication strategies that improve machining performance while considering efficient use of manufacturing resources. This study examines the sustainability-related implications of carbon nanofluid-based minimum quantity lubrication (MQL) using multiple measured machining performance indicators. Carbon nanopowder (CNP) and carbon nanofiber (CNF) were incorporated into distilled water and vegetable oil at selected concentrations, with the base fluids used as control conditions. The formulations were evaluated based on flow rate, cooling rate, viscosity, frictional force, tool wear rate and surface roughness to characterise lubricant delivery, thermal performance, fluid rheological behaviour, tribological response, tool utilisation and measured surface quality. The results showed that carbon-based formulations generally improved the measured machining responses, although their effects varied according to additive type and base fluid. The 0.6 g CNP–vegetable oil formulation achieved the highest cooling rate of 1.30 °C/min, the lowest frictional force among the vegetable-oil formulations at 0.71 N, the lowest tool wear rate of 0.0097 mm/min, and the lowest surface roughness of 0.15 µm. These results indicate favourable thermal, tribological, tool-wear and surface-quality responses compared with the corresponding vegetable-oil control. The combined findings suggest potential resource-efficiency benefits associated with reduced tool wear and improved surface quality, although downstream reductions in tool consumption and finishing requirements were not directly measured. Overall, 0.6 g CNP in vegetable oil exhibited the most favourable combination of measured machining responses among the formulations investigated. The study provides a sustainability-oriented evaluation of carbon nanofluid-based MQL by relating measured machining performance to potential resource-efficiency implications, while recognising that comprehensive environmental, economic and occupational sustainability assessment requires additional direct measurements.