Numerical study of flow and thermal characteristics in titanium alloy milling with hybrid nanofluid minimum quantity lubrication and cryogenic nitrogen cooling

The flow and heat transfer characteristics in titanium alloy (Ti-6Al-4V) milling with a hybrid nanofluid minimum quantity lubrication (nMQL) and cryogenic nitrogen lubrication/cooling method is numerically analyzed for two different cryogenic spraying conditions of N₂ (sensible cooling) and LN₂ (latent cooling), and three different nMQL nozzle spray angles of 0˚, 45˚, and 90˚. The volume of fluid (VOF) model is employed to track the interface between each fluid, which is air, N₂, and LN₂. The discrete phase model (DPM) is used to solve the trajectory and temperature of nMQL droplets. The heat generation occurred during the milling process, and the phase change of the liquid nitrogen is modeled using the user-defined functions (UDF) in ANSYS Fluent. The results show that the LN₂ spraying condition provides extremely effective cooling of the Ti-6Al-4V workpiece and tungsten carbide (WC) tool in the Ti-6Al-4V milling process. However, increased nMQL droplets pass through the cutting zone under the N₂ spraying condition, enhancing the lubrication. Moreover, the 0˚ nMQL spray angle is found to be best suited for improved cooling and lubrication performance under both the N₂ and LN₂ spraying conditions.