Effect of elliptical vibration trajectories on grating structure formation and its application in structural coloration

Structural coloration, which utilizes the optical interactions between the periodic nanostructures and visible light to render iridescent or non-iridescent colors, has been a fascinating research topic in recent years. The rendering performance of artificial structural color is subject to the nanofabrication capability and structure accuracy. In this paper, an innovative elliptical vibration texturing method has been introduced for fast generation of periodic controllable grating structures, which can be utilized as reflective gratings for rendering iridescent structural color effects. Firstly, the effect of different elliptical vibration trajectories on the formation of grating structure is theoretically analyzed and experimentally verified. Secondly, the structural coloration based on the grating formation is demonstrated; and the relationship between the color effect and grating profiles is studied. Specifically, different elliptical trajectories, which are commonly used in vibration-assisted machining, are generated by a newly-proposed non-resonant vibration cutting tool and employed for the generation of periodic grating structures. An analytical model for the prediction of grating profile is established, which takes into account the tool vibration trajectory and tool geometry. It is found that the orientation and periodic distance of grating structures can be precisely controlled, while the cross-section profile has a strong dependence on the vibration trajectories. The results indicate that tilted elliptical trajectories with at least a 3 μm vibration amplitude in the depth-of-cut (DOC) direction are favorable for the generation of high aspect-ratio grating structures. An insufficient DOC vibration amplitude (less than 3 μm) leads to the reduced effective chip thickness and unstable plastic chip removal. The elastic recovery effect becomes significant and deteriorates the formation of desired grating structures. Subsequently, the iridescent color effects are demonstrated and compared between samples produced with different tool vibration trajectories. The hue and brightness of induced colors are independently determined by the periodic distance and cross-section profiles of generated grating structures. The proposed non-resonant vibration texturing method provides a new manufacturing method for realizing structural colors in addition to the existing nanofabrication processes.