Oil mist concentration and machining characteristics of SiO2 water-based nano-lubricants in electrostatic minimum quantity lubrication-EMQL milling

Abstract

• SiO 2 nano-lubricant droplets presented better chargeability and more likely to be affected by electrostatic force to adsorb and deposit. • SiO 2 nano-lubricant showed higher penetrability after charging compared with vegetable oil. • The adsorption quantities of the charged SiO2 nano-lubricant droplets were larger than those of the charged vegetable oil droplets. • SiO 2 nano-lubricant EMQL showed much lower oil mist concentration and alternative machining performance of traditional oil-based MQL. Minimum quantity lubrication (MQL) machining is an advanced near dry cutting technology in modern machining field. However, the cutting oil mist produced during the process of oil-based MQL affected the ambient air quality and endangered the health of employees. To avoid this drawback, a novel lubrication/cooling method called electrostatic minimum quantity lubrication (EMQL) which used SiO 2 water-based nano-lubricant as cutting fluid was proposed. The charge mass ratio, surface tension and contact angle of SiO 2 water-based nano-lubricant and vegetable oil with different charging voltages were compared, and the penetration performance of these two lubricants was analysed using capillary dynamics equation. The adsorption and deposition properties of oil mist produced by different lubrication methods were investigated, and revealed the adsorption and deposition mechanisms of the charged droplet. The influences of the charging voltage, flow rate, air pressure, spindle speed and cutting depth on PM10 and PM2.5 concentrations under different lubrication conditions were revealed. Finally, the milling performance of SiO 2 water-based nano-lubricant EMQL of stainless steels was evaluated comparatively. The results showed that SiO 2 water-based nano-lubricant presented better chargeability compared with vegetable oil, and thus displayed stronger penetrability, adsorption and deposition capacity. SiO 2 water-based nano-lubricant EMQL with -4 kV showed the lowest oil mist concentration and similar machining performances compared with the vegetable oil MQL, and the concentration values were close to the standards set by the National Institute for Occupational Safety and Health (NOISH). The charged SiO 2 water-based nano-lubricant droplets with excellent charging performance presented better adsorbability and penetrability, so that the charged droplets were prone to be electrostatic adsorbed in the machine tool and penetrated into the cutting region, which reduced the oil mist content in the machining environment and presented alternative cutting performance.