Abstract: To overcome the technical difficulties for accurately predicting and controlling the 3D topography of nanoscale blazed gratings induced by ultrasonic elliptical vibration cutting, an iterative surface updating method for grating 3D topography is proposed by considering the synthetic cutting trajectory, three-dimensional geometric characteristics of cutting tool as well as workpiece material properties. The effect of minimum uncut chip thickness and intensive interaction between tool flank and machined surface are also included. Taking the ideal grating 3D topography with 1μm spacing, 12 ° blazed angle and 106 nm grating height as an example, the deterministic generation of blazed grating with desired 3D topography is realized by setting the process parameters based on the above method. The experimental results show that the machining errors of grating spacing, blazed angle and grating height are 1.1%, 4.1% and 15.0% respectively, which indicates the feasibility and accuracy of the proposed control method for 3D topography of blazed gratings. The technical paths to further improve the machining accuracy of blazed gratings are then discussed. In addition, the machined grating quality does not deteriorate with the increment of cutting distance as no obvious tool wear around the cutting edge being observed even when the cumulative cutting distance exceeds 10 meters.

Key words: blazed gratings, ultrasonic elliptical vibration cutting, 3D topography, ultra-precision machining, micro/nano-structures