Key Takeaways & Executive Findings
- •• A novel Nepenthes-inspired microtexture on cutting tool rake faces enables controlled lubricant transport, overcoming lubrication limitations in continuous cutting. • A dynamic model for lubricant transport in open microchannels was developed, achieving 5.01% average prediction deviation and 4.72% improvement over the classical Lucas-Washburn model. • The T2 surface exhibited the strongest unidirectional diffusion, with contact angle ratio 0.48, droplet unidirectional spreading ratio 1.75, and droplet spreading aspect ratio 3.99. • Micro-textured surfaces in MQL turning enhance anti-wear, friction-reducing, and efficiency, supporting sustainable machining of difficult-to-machine materials.
Abstract
During the metal cutting process, especially in continuous contact conditions like turning, the challenge of lubricants failing to effectively reach the cutting point remains unresolved. Micro-textured cutting tools offer a potential solution for tool-chip contact challenges. Inspired by the evolutionary achievements of the biosphere, micro-textures are expected to overcome lubrication limitations in cutting zones. Drawing on the anti-gravity water transport seen at the mouth edge of the Nepenthes plant, an innovative microchannel with Nepenthes-shaped contours was designed on the rake face to enable controlled lubricant transport. However, the dynamics of lubricant delivery on textured surfaces are not fully understood. This study first analyzed the microstructure and water transport mechanism of Nepenthes to reconstruct a micro-textured surface for controlled lubricant transport. A dynamic model was then developed to describe lubricant transport within open microchannels, with mathematical simulations predicting transport speed and flow distance. To validate this model, diffusion experiments of alumina soybean oil nanolubricant on polycrystalline diamond (PCD) cutting tool surfaces were conducted, showing an average prediction deviation of 5.01%. Compared with the classical Lucas-Washburn model, the new model improved prediction accuracy by 4.72%. Additionally, comparisons were made to examine droplet spreading and non-uniform diffusion on textured surfaces, revealing that the T2 surface exhibited the strongest unidirectional diffusion characteristics. The contact angle ratio, droplet unidirectional spreading ratio, and droplet spreading aspect ratio were 0.48, 1.75, and 3.99, respectively. Finally, the anti-wear, friction-reducing, and efficiency-enhancing mechanisms of micro-textured surfaces in minimum quantity lubrication turning were analyzed. This approach may support continuous cutting of difficult-to-machine materials.
1. Introduction
In machining operations, cooling and lubrication are essential. During cutting, the high-speed rotation of the tool in contact with the workpiece generates friction and heat [1, 2]. Inadequate cooling can lead to workpiece deformation, tool wear, and other issues [3]. To address this, cutting fluids have become widely used [4, 5], serving functions such as cooling, lubrication, friction reduction, and chip removal, which improve machining efficiency and quality [6–8]. However, concerns about potential skin diseases, respiratory risks for operators, and environmental pollution have raised questions about cutting fluids [9–12]. Due to these concerns, there is a pressing need to transform and upgrade traditional cooling and lubrication practices.
With advancements in sustainable machining, attention has shifted to minimum quantity lubrication (MQL) techniques [13–15]. Compared to traditional methods, MQL not only ensures effective lubrication but also significantly reduces fluid consumption, thereby lowering both costs and environmental pollution [16, 17]. MQL also enhances machining precision and surface quality [18, 19]. Nanofluid-based MQL is a more efficient approach developed to address heat transfer limitations within MQL applications [20–22]. However, in continuous cutting, a bonding contact area at the tool-chip interface prevents effective nanofluid injection [23]. Lubricants at the friction interface cannot actively control penetration.
To address these issues, researchers have explored modifying the contact state at the tool-chip friction interface [24, 25]. Microtextures with specific patterns and sizes on cutting tool surfaces can reduce interface friction during cutting [26, 27]. These microtextured surfaces retain lubricating fluids and microchips, reducing the contact area between the tool and chips [28, 29]. Changes in the geometry of the tool-chip contact surface affect the flow field and contact pressure within the cutting area [30, 31]. Moreover, microtextures offer a microspace for better fluid infiltration at the cutting point.
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Xiaoming Wang, Min Yang, Teng Gao, Lan Dong, Yusuf Suleiman Dambatta, Xin Liu, Yuying Yang, Qinglong An, Yanbin Zhang, Changhe Li (2025). Lubricant Transport Mechanism and Dynamics Model for Nepenthes-shaped Biomimetic Microtexture. Chinese Journal of Mechanical Engineering. https://doi.org/10.1186/s10033-025-01197-8
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Frequently Asked Questions
What is the main challenge in lubricating cutting tools during continuous cutting?
In continuous cutting, the tool-chip interface forms a bonding contact area that prevents effective nanofluid injection, so lubricants cannot actively penetrate the friction interface.
How does the Nepenthes-inspired microtexture improve lubricant transport?
The microtexture, designed with Nepenthes-shaped contours on the rake face, enables controlled lubricant transport through open microchannels, overcoming the limitations of conventional lubrication in cutting zones.
What is the accuracy of the proposed dynamic model for lubricant transport?
The model predicts transport speed and flow distance with an average deviation of 5.01% from experimental results, and improves prediction accuracy by 4.72% compared to the classical Lucas-Washburn model.
Which surface exhibited the strongest unidirectional diffusion characteristics?
The T2 surface showed the strongest unidirectional diffusion, with a contact angle ratio of 0.48, droplet unidirectional spreading ratio of 1.75, and droplet spreading aspect ratio of 3.99.
What are the benefits of micro-textured surfaces in MQL turning?
Micro-textured surfaces in MQL turning enhance anti-wear, friction-reducing, and efficiency, supporting sustainable machining of difficult-to-machine materials.
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