Characterization of Lubricant Droplets for Internal Minimum Quantity Lubrication

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

Characterization and Performance of Minimum Quantity Lubricants in Through-Tool Drilling

This study characterized airborne microdroplet diameters and size distribution from two commercially available lubricants A and B for internal minimum quantity lubrication (MQL). The effects of air pressure, oil channel size, physical properties of lubricants on the resultant microdroplets and through-tool MQL drilling performance were studied. Airborne microdroplet diameters were highly sensitive to the coolant channel sizes and air pressure. Cluster method was used to divide microdroplets into smaller clusters for comparison. Experimental data show that the average airborne microdroplet of lubricant B was larger than that of lubricant A at different air pressures and channel sizes. The contact angle of lubricant A was at least 10° less than that of lubricant B when depositing on glass or aluminium. High-speed imaging showed the tendency of more viscous lubricant B sticking to the drill tip, and higher pressure and longer time was required to atomize this viscous oil. Built-up-edges were less significant when drilling A380 aluminium with lubricant A. Due to high machinability of A380 aluminium, variation of hole diameter and hole cylindricity were minimal when drilling with different lubricants. Insignificant improvement in hole quality was observed when drilling with excessive amount of MQL lubricants or high concentration of lubricant C in flood coolant