Charging mechanisms and atomization dynamics in electrostatic field-driven bio-based MQL

Electrostatic field-driven minimum quantity lubrication (EMQL) demonstrates unique advantages in enhancing lubrication and cooling performance of droplet. However, while considerable research has focused on evaluating the machining performance of EMQL, the underlying charging mechanisms and atomization dynamics of bio-based lubricants remain unclear. This study introduces a novel charging nozzle that employs both contact and corona charging mechanisms. It then investigates the charging mechanisms of biolubricants based on electric field distribution characteristics. Furthermore, the charging, atomization, and spreading performance of various biolubricants are experimentally evaluated. The results demonstrate that the combined contact-corona charging nozzle significantly enhances surface charge density in both droplets and the cutting zone, compared to conventional contact charging nozzles. Biolubricants with high electric conductivity additives show superior charging properties over pure vegetable oil. Increasing the applied voltage from 0 to 35 kV leads to substantial reductions in mean droplet diameter: 28.83% for rapeseed oil, 38.94% for lecithin-oil mixture, 35.76% for WS 2 nanofluids, and 38.28% for CNT nanofluids. Atomization dynamics analysis reveals that the presence of charges on droplet surfaces and the electric field at the nozzle both contribute to enhancing the atomization performance of biolubricants. However, higher conductivity accelerates interfacial charge release, which inhibits electrically driven droplet spreading. This study provides valuable insights into the EMQL mechanism through experimental and theoretical analysis, expanding the potential applications of charged biolubricants in clean manufacturing and tribology.