Lubricant Transport Mechanism and Dynamics Model for Nepenthes-shaped Biomimetic Microtexture

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.