Experimental investigation on mixed spray characteristic of cryogenic nano-minimum quantity lubrication in milling nickel base superalloy

The GH4169 nickel-based superalloy, renowned for its exceptional mechanical properties, presents significant challenges in machining due to its inherent hardness and thermal resistance. This study investigates the application of a hybrid nano-lubricant coolant mixture, combining multiwalled carbon nanotube nanofluid-assisted minimum quantity lubrication (MWCNT–MQL) with cryogenic liquid nitrogen (LN2), and sprays it through a single nozzle to improve the machinability of GH4169. A computational fluid dynamics (CFD) analysis of the multiphase, mixed-lubricated coolant spray under turbulent flow conditions was performed using the discrete phase model (DPM) in ANSYS Fluent software. Additionally, to enable precise mixing of the dual-phase coolant, a custom-designed mixing chamber was fabricated. Droplet size distribution was conducted using spray footprint analysis, and end-milling experiments evaluated cutting force, surface hardness, roughness, and tool wear under varying spray pressures (2–6 bar) and flow rates (40−60ml/h). The results revealed that the spray with the mean average droplet size (16.76μm at 4 bar and 50ml/h) yielded the most favorable outcomes. This resulted in a cooler workpiece surface, leading to increased surface hardness and cutting force. Additionally, a significant reduction in surface roughness and tool wear was observed. Compared to dry machining, hybrid lubri-cooling enhanced machinability and extended tool life by up to 43.16%, as confirmed by milling experiments and wear analysis.