Through-Tool Minimum Quantity Lubrication and Effect on Machinability of Inconel 718

Abstract

This thesis simulated through-tool minimum quantity lubrication (MQL) to experimentally characterize micromist lubricant droplets. The effect of nozzle surface roughness and air pressure was analyzed to study the lubricant droplets’ size, distribution and exit air velocity. MQL at different conditions was used in micromilling of Inconel 718 blocks that were additively printed by selective laser melting technique. A 3D printed nozzle simulated internal flow in commercially available drill with internal cooling channels. Anemometer was used to measure the exit air velocity of the droplets.

Droplets were collected on a glass plate from which airborne diameters and standard deviation were calculated. The droplet diameter and distribution were most sensitive when using nozzle having a rough surface with the mean airborne droplet diameter being 4.69 µm at 550 kPa. Mean airborne droplet diameter increased to 7.60 µm when the smooth nozzle was used at 550 kPa. Micromist generated from a rough nozzle at 550 kPa with a maximum air velocity of 13.1 m/s improved tool life by effectively lubricating the tool workpiece interface. The tool wear was reduced to approximately 41 µm from 49 µm measured with the use of smooth nozzle at 275 kPa. It also produced micromilled slots with surface finish Sₐ of 1.5 µm.