Lubricant activity enhanced technologies for sustainable machining: Mechanisms and processability

The use of Minimum Quantity Lubrication (MQL) with bio-lubricants has been extensively studied in aerospace sustainable manufacturing. Enhanced MQL technologies have been proposed to reduce tool wear and improve workpiece surface integrity by increasing lubricant activity. However, the relationship between enhancement behavior, physicochemical properties of bio-lubricants, and processability remains unclear, presenting challenges for MQL technologies, particularly with difficult-to-machine materials. To address this gap, this paper provides an in-depth mechanism analysis and a comprehensive quantitative evaluation of the machinability of enhanced MQL technologies, considering chemistry, molecular dynamics, fluid dynamics, tribology, and heat transfer. Firstly, the cooling and lubrication enhancement mechanisms of nano-lubricants were systematically summarized, focusing on molecular structure, physical properties, and preparation processes. Secondly, the atomization enhancement mechanism of Electrostatic Minimum Quantity Lubrication (EMQL) was analyzed, revealing a 49% reduction in PM2.5 concentration during the atomization process compared to conventional MQL. Thirdly, the transport and infiltration enhancement mechanisms of bio-lubricants in cutting and grinding zones were summarized, incorporating electromagnetic fields and ultrasound-assisted processes. Finally, for cutting and grinding applications involving difficult-to-machine materials in aerospace, the optimized machinability of enhanced MQL technologies was concluded, showing a 50.1% increase in lubricant heat transfer coefficient and a 31.6% decrease in grinding temperature compared to standard MQL. This paper aims to help scientists understand the effective mechanisms, formulate process specifications, and identify future development trends in this technology.