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

Abstract

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.

Electrostatic atomization minimum quantity lubrication machining: from mechanism to application

“…Their results showed that CMR increased with the growth of voltage under all conditions [224,225]. Given that the tested liquids were nonpolar and better insulating specimens, the droplets were less chargeable at the lower voltages, as verified also in the experiments of Wang et al, who concluded that the higher the conductivity, the greater the chargeability of the liquid [233].…”

“…the diameter of a sphere with the same volume and surface area ratio as the particles, which is used to estimate the average size of a given particle distribution [222,223]). The SMD of the droplets obtained at a charging voltage of −12 kV was 34.3% smaller than that obtained by MQL [224]. This result indicates that the atomization quality of the EMQL is higher than that of the conventional air-assisted MQL.…”

“…Furthermore, electrostatic atomization results in smaller and more uniformly distributed droplets with reduced air pressure; this scenario does not result in small droplets migrating outside the deposition zone by air pressure. Furthermore, the droplet charge increases the surface activity and decreases the surface tension [224], which greatly enhances the ability of the droplet to spread in the cutting zone (figure 19(a)). The high viscosity of the biolubricant and its high surface tension are not conducive to heat transfer and its spreading to the cutting zone, which can limit the use of biolubricants.…”

Analysis of electrostatic solid lubricant spray process parameters during turning Ti-6Al-4V alloy

“…The reduction of friction and temperature takes place by cooling and lubrication action which eventually improves surface roughness. 15 During machining of hard-to-cut with high-speed turning, high-velocity cooling is a favourable technique for better improvement of usage of cutting tool and surface roughness in terms of proper cooling and lubrication. 27 Application of continuous coolant droplets indicates wettability at tool–chip interface and caused easy chip breakage into small segments.…”

“…14 A sufficient and more droplet transfer rate of coolants and lubricants with extended adhesion time is required for a high-temperature cutting region in which the applied thin lubricant films reduce the tool wear and improving surface quality of the workpiece. 15–18…”