Numerical and experimental investigation of the droplet size for MQL aerosol under different operating parameters with Flow visualization

Abstract

Minimum quantity lubrication (MQL) is a sustainable machining process in which oil and air are mixed to form a spray that can be directed to the cutting zone. MQL spray factors like droplet size and velocity and their effect on machining remain unclear, especially when employing diverse oils and operating settings. Mist formation factors determine how well spray droplets lubricate the targeted area during machining. Numerical and Experimental studies were conducted with different values for MQL parameters like cutting oil type, air pressure and oil flow rate, to establish the best possible combination to give the ideal droplet size and surface roughness. The study utilized three types of oils and varied air pressures to evaluate the cooling effectiveness of MQL spray during end milling operations. Experimental droplet size and velocity measurements were obtained using ‘Phase Doppler Anemometry (PDA)’ and ‘Particle Image Velocimetry (PIV)’ techniques. A numerical model within ANSYS Fluent software, employing computational fluid dynamics (CFD), predicted spray flow properties and was validated using PIV data. Raising the air pressure decreased the droplet size, while increasing velocity to achieve greater overall speed and enhanced lubrication in the cutting region. Changing the coolant flow rate or the compressed air pressure affected the Sauter mean diameter (SMD) of oil particles. The research showed that increasing air pressure from 1 bar to 3 bar reduced surface roughness by 55.40 percent and SMD by 24.58 percent for 120V oil. Among the three cutting oils tested, the 120V oil achieved the lowest surface roughness at 0.227μm under specific conditions: a flow rate of 150 ml hr−1, pressure of 3 bars, and SMD of 35.5 μm. These findings provide valuable insights into improving MQL efficiency for machining operations.