Soybean oil-based nanofluid-assisted MQL for sustainable drilling of LPBF Ti6Al4V: effects on tool wear and surface integrity

Ti6Al4V is widely used in aerospace and biomedical applications but is renowned as a difficult-to-machine material due to its thermo-physical characteristics, often leading to premature tool failure and compromised product finishes. The advent of additive manufacturing (AM) technologies has partly alleviated these issues, enabling the production of near-net-shape complex geometries and shortening the process chain. Nonetheless, finishing machining operations are often required to achieve the final shape. In parallel, the increasing demand for greener processes has driven research towards innovative lubricating strategies. Among these, nanofluid-assisted minimum quantity lubrication (NMQL) using vegetable-based nano-cutting fluids has gained growing attention. Nanoparticles are suspended in the main cutting fluid to enhance its thermal and tribological performance, generating a nanofluid, overcoming the inherent limits of vegetable oils regarding their natural heat dissipation and load resistance. In this framework, a comparison between pure soybean oil and a soybean oil-based nanofluid composed of 0.1 wt.% Al₂O₃ nanoparticles and 0.32 wt.% surfactant is proposed when drilling laser powder bed fusion (LPBF) Ti6Al4V samples. Viscosity, wettability, and tribological characteristics were evaluated for both cutting fluids. Tool wear was evaluated and quantitatively assessed through optical and SEM imaging. Hole internal surface quality was assessed through topography and morphology analyses. The results showed that the NMQL approach effectively reduced tool wear compared to conventional MQL with pure soybean oil, achieving a 47% reduction in wear area. Nanoparticles enhanced the tribological characteristics of the base oil and apparently promoted a “rolling-effect” mechanism at the tool/workpiece interface.