A study on the fluid film of an atomization-based cutting fluid (ACF) spray system during titanium machining

The poor thermal conductivity and low elongation–to–break ratio of titanium lead to the development of extreme temperatures localized in the tool–chip interface during machining of its alloys and cause accelerated tool wear. The atomization–based cutting fluid (ACF) spray system has recently been demonstrated to improve tool life during titanium machining. The penetration into the tool–chip interface by means of the thin fluid film created by the ACF spray system appears to be the mechanism by which tool life is extended. However, there is a lack of a physics-based understanding of the development of the fluid film created by the ACF spray system and its resulting cooling and lubrication properties during titanium machining. The research presented in this thesis characterizes the development of the fluid film created the ACF spray system and investigates the resulting changes in cutting temperatures and friction inside the tool–chip interface during titanium machining. To accomplish this, ACF spray experiments are performed in order to observe the nature of the spreading film, while titanium machining experiments are performed to determine the temperature reduction inside the tool-chip interface, respectively. A physics-based model of the fluid film development is proposed in order to predict the thickness and velocity of the fluid film and study the tool-chip interface fluid penetration behavior. On the experimental front, ACF spray experiments are performed by varying impingement angle in order to observe the nature of the spreading film and to determine the film thickness at different locations after impingement of the droplets. It is observed that the film spreads radially outward producing three fluid film development zones (i.e. impingement, steady, unsteady). The steady zone is found to be between 3 and 7 mm from the focus (impingement point) of the ACF spray for the set of parameters investigated. Fluid film penetration of the tool-chip interface is observed during titanium machining. The temperature gradient and mean cutting temperature are also measured using the inserted and the tool–work thermocouple techniques, respectively, during titanium machining with the application of the ACF spray system. Cutting temperatures for dry machining and machining with flood cooling are also characterized for comparison with the ACF spray system temperature data. Findings reveal that the ACF spray system more effectively reduces cutting temperatures over flood cooling. The tool–chip friction coefficient data indicate that the fluid film created by the ACF spray system also actively penetrates the tool–chip interface to enhance lubrication during titanium machining, especially as the tool wears. On the modeling front, an analytical three-dimensional (3D) thin fluid film model for the ACF spray system has been developed based on the continuity equations for mass and momentum. The model requires a unique treatment of the cross–film velocity profile, droplet impingement and pressure distributions, as well as a strong gas–liquid shear interaction. The analytical film model is validated via a comparison of the predicted and experimentally measured fluid film thickness profiles. The model predictions of film velocity also reveal that the fluid film created by the ACF spray system can readily penetrate into the entire tool–chip interface during titanium machining