Generation of high-saturation two-level iridescent structures by vibration-assisted fly cutting

The submicron-level structured surface induces viewing-angle-dependent iridescence, and has wide applications in multi-color printing, micro-display projection, invisibility cloak technology. In this study, several types of two-level structures, which consist of the first-order micro geometric features corresponding to the pattern shape and the second-order submicron grooves corresponding to the diffraction grating, are designed to directly induce a variety of iridescent patterns based on their shape regulations. To fabricate these two-level iridescent structures with high accuracy in a single step, vibration-assisted fly cutting (VAFC) is proposed. VAFC involves the low-frequency vibration of the workpiece in the vertical direction during the feed in the horizontal direction and the high-speed rotation of the diamond cutting tool. A 3D theoretical model is established for the numerical simulation of the generating process of the iridescent structures and the regulation of the first-order geometric feature by vibration parameters. As the key parameter to the iridescent color, the spacing of the second-order submicron grooves is flexibly controlled by the feed rate. A VAFC platform is developed to fabricate the two-level structures and an optical detection system is setup to test the surface iridescence. Various vivid colors are regulated by the two-level structures with high saturation and uniformity.