Tribological Performance and Lubrication Mechanism of Contact-Charged Electrostatic Spray Lubrication Technique

To minimize friction at the chip–tool interface and the amount of lubricant usage, a new near-dry machining technique called “contact-charged electrostatic spray lubrication (CCESL) technique” was proposed. The chargeability, penetrability, and wettability of lubricant droplets under CCESL condition were analyzed. The atomization and tribological performance of the CCESL technique were compared with those of the existing minimal quantity lubrication (MQL) technique under different testing conditions. The experimental results suggest that the CCESL technique considerably improves the anti-wear and anti-friction properties compared with the existing MQL technique. In addition, to understand its lubrication mechanism, the morphology and main elements of the worn surface were characterized using an optical microscope and X-ray photoelectron spectroscopy, respectively. In the CCESL technique, an ordered molecule layer which provides effective lubrication is formed on the rubbing surface as polar functional groups in the lubricant molecule are oriented. The enhanced tribological performance is attributed to the fact that the technique can provide more abundant lubricant and oxygen for the interface of frictional pairs to promote the formation of an abundant lubricating layer comprising adsorption and oxide films, which improve the worn surface quality.