| dc.description.abstract | This study characterized airborne diameter and distribution of two commercially available lubricants’ droplets for internal minimum quantity lubrication (MQL). The effect of varying air pressure on the resultant droplets and drilling performance was studied.
Resultant droplet sizes and contact angles on A380 aluminum were evaluated. Droplet formation at the drill tip was investigated with a high-speed camera. Drilling tests with MQL, flood coolants, and dry condition were performed to validate the effectiveness of through tool MQL.
Airborne droplet diameters were highly sensitive to the coolant channel sizes. Overall, the airborne droplets of Castrol oil were larger than that of Coolube oil at different air pressures and drill sizes. Contact angle of Coolube oil is about half of that for Castrol oil. High speed imaging showed the tendency of high viscosity Castrol oil sticking to the drill tip. Built-up-edges were significant when drilling A380 aluminum with Castrol oil. Due to high machinability of A380 aluminum, the hole diameter and hole cylindricity were the same when drilling with MQL or flood coolant, excessive amount of MQL lubricant did not improve the hole quality, but without coolant the hole cylindricity doubled.
The result of this study will be applied for high aspect ratio drilling of A380 aluminum engine blocks. The same procedure can be extended to study deep hole drilling of difficult-to-machine alloys and additively manufactured metals. | |
