Development and validation of theoretical model for nanofluid minimal quantity lubrication selection in aviation difficult-to-machine materials

Difficult-to-machine aeronautical materials like ceramic matrix composites exhibit high strength and complex machinability, leading to high cutting forces, temperatures, and poor surface quality. Nanofluid minimum quantity lubrication (NMQL) offers excellent friction-reduction and heat-transfer performance, but nanofluid parameter selection remains empirical, lacking theoretical support, which limits its broader engineering application. Accordingly, a theoretical model for nanofluid selection was established by comprehensively considering tribological characteristics, thermophysical properties, dispersion stability, particle concentration, and material compatibility, and was solved using a multi-objective particle swarm optimization algorithm. The input parameters of the model include the physical properties and interfacial behavior characteristics of various base oils and nanoparticles, while the output is the optimal NMQL combination scheme. Results showed that, when applied to 2.5D SiC_f/SiC composites, the optimal solution determined and experimentally validated was palm oil-carbon nanotubes (CNTs)-vol. 2 %. In terms of machining performance, compared with dry grinding (DG), the grinding force under NMQL-CNTs-2 % condition decreased by up to 75.2 %, and the surface roughness decreased by 41.81 %. Meanwhile, the number of rough fracture surfaces was minimized, and fiber wear was minimal, indicating the high accuracy of the optimal solution. In addition, validation was performed using experimental data from existing studies on Ti6Al4V titanium alloy, GH4169 alloy, carbon fiber reinforced polymer (CFRP) composites, and quartz fiber reinforced polyimide (QFRP) composites. The predicted results from the model were consistent with the experimental findings, further demonstrating its applicability and generalizability. The study effectively guides nanofluid selection while providing theoretical support for high-efficiency, precision machining of aeronautical difficult-to-machine materials.