A novel approach to improve environmentally friendly machining processes using ultrasonic nozzle–minimum quantity lubrication system

Abstract

In minimum quantity lubrication (MQL) machining, a small quantity of cutting fluid is air-atomized to generate fine liquid droplets, and they are injected into the machining zone. The effectiveness of the MQL system depends on the droplet size/distribution, spray shape, spray velocity, and area fraction covered by the droplets. In the present study, for the first time, a novel MQL nozzle has been designed and manufactured applying ultrasonic vibrations using piezoelectric discs tighten on the nozzle between the mechanical amplifying element and a support element. Ultrasonic vibrations can be used to effectively atomize the cutting fluid into fine and uniform-sized droplets and smaller spray angle with a larger spray deposition distance. Ultrasonic nozzle–minimum quantity lubrication (UN-MQL) system generates a mist-like uniform spray. The ultrasonic nozzle was designed and analyzed using the SolidWorks and Ansys Workbench software. Image processing techniques have been used to characterize the droplet sizes, and the droplet distribution after the oil has been sprayed onto a polished lead-coated plate by UN-MQL system as well as better understanding in the application of the ultrasonic nozzle for its effective use in practical industrial applications. A set of experiments have been conducted on AISI 304L stainless steel during turning with the developed setup, and the results have been compared with dry, wet, and conventional MQL turning processes. The fine droplets produced by the UN-MQL system penetrate effectively into the machining zone and consequently enhance the cooling-lubrication characteristic in the cutting zone. Spray angle of UN-MQL in comparison to conventional MQL systems decreased about 40% and 30% in air pressure of 6 and 3 bar, respectively. The rising inclination of the area fraction covered by droplets in variable air pressures has improved approximately 70% among the oil flow rates of 16 to 110 ml/h in the UN-MQL case as opposed to the conventional MQL system. The greatest quantity of decrement in mean droplet diameter which transpired in air pressure of 1 bar, reached nearly 63% for the oil flow rates of 16 ml/h, 30 ml/h, and 43 ml/h. Overall, the results obtained during UN-MQL turning experiments show that the surface roughness has been improved compared to dry, flood, and conventional MQL turning processes.