With the advantage of high light intensity due to low scatting, structural colors generated by metallic diffraction nanograting structures, used as a type of diffractive optical element, have shown great potential for application in industrial and scientific research fields such as optical anti-counterfeiting and sensors. Within the visible light wavelength range, the diffraction performance is highly dependent on the height and shape consistencies of the nanograting. However, there is still room for the improvement in the flexible control over structure formation through mechanical nanomachining within this scale. The novelty of this paper lies in proposing a machining strategy for nanograting structures with variable heights through precise regulation of the revolving trajectory using tip-based nano down-milling. It explores how different geometric features of trajectories impact the amount of material deformed into a grating and its distribution shape, referred to as undeformed grating area. By analyzing the forming mechanisms of nanogratings under various trajectories with finite element simulation, the desired undeformed grating area is successfully achieved, which is mainly extruded by the tip flank face to form the right facet of the grating, resulting in a small deformation degree and a high deformation efficiency. Three distinct types of revolving trajectories are filtered out according to five quantitative evaluation indicators for machining performance, namely material plastic deformation, grating profile consistency, grating height consistency, machining forces, and area transforming height, and then are compared in processing nanogratings with different heights. It is obtained that only by regulating the vertical vibration amplitude of the revolving trajectory, the semicircle trajectory with the optimal geometric features has the ability to machine high-quality nanograting structures with a continuous height variation of up to 220 nm in a spacing of 400 nm.

A modified five-axis cutting system using a force control cutting strategy was to machine indentations in different annuli on the entire surface of a target ball. The relationship between the cutting depths and the applied load as well as the microsphere rotation speed were studied experimentally to reveal the micromachining mechanism. In particular, aligning the rotating center of the high precision spindle with the microsphere center is essential for guaranteeing the machining accuracy of indentations. The distance between adjacent indentations on the same annulus and the vertical distance between adjacent annuli were determined by the rotating speed of the micro-ball and the controllable movement of the high-precision stage, respectively. In order to verify the feasibility and effect of the proposed cutting strategy, indentations with constant and expected depths were conducted on the entire surface of a hollow thin-walled micro-ball with a diameter of 1 mm. The results imply that this machining methodology has the potential to provide the target ball with desired modulated defects for simulating the inertial confinement fusion implosion experiment.