Tool wear in enhanced minimum quantity lubrication assisted milling: from mechanism to application

Milling is widely used in aerospace structures, molds, automotive parts, and other mechanical parts manufacturing fields. However, milling tool wear is a serious constraint on the production quality, cost control, and productivity of parts. Traditional flood milling depends on large quantities of cutting fluid for cooling and lubrication. Although cutting fluid plays an important role in the cutting of metal materials, this large-scale use not only causes serious pollution of the environment but also poses a threat to the health of workers. As an ideal alternative to cutting fluid, eco-friendly lubricant-based Minimum Quantity Lubrication (MQL) is attracting attention for its clean and sustainable properties. However, when it comes to efficiently milling difficult-to-machine materials, MQL technology still faces technical challenges in terms of mechanical and thermal damage, making it difficult to meet stringent surface integrity requirements. To improve the performance of MQL, enhanced MQL technologies including Nano-lubricant Minimum Quantity Lubrication (NMQL), Cold Plasma (CP) enhanced Minimum Quantity Lubrication (CPMQL), Ultrasonic Vibration (UV) enhanced Minimum Quantity Lubrication (UVMQL), and Cryogenic Minimum Quantity Lubrication (CMQL) have been applied to milling processes. This paper reviews the recent research advances in enhanced MQL technologies and elucidates the key scientific issues. First, the tribological and heat transfer mechanisms of the milling area in MQL-assisted milling are summarized, and the bottleneck of insufficient cooling and lubrication is analyzed. Subsequently, the mechanisms of different enhanced MQL-assisted technologies are summarized and revealed, and the Coefficient Of Friction (COF), milling force, milling temperature, and tool wear under different enhanced MQL conditions are comparatively evaluated. Finally, the research gaps and future exploration directions of enhanced MQL-assisted milling technology are envisioned. It makes it convenient for researchers to gain a deeper understanding of the mechanism, tribological behavior, and development trend of enhanced MQL technology.