Novel Disc Hydrodynamic Polishing Process and Tool for High-Efficiency Polishing of Ultra-Smooth Surfaces.

Nowadays, large aspheric surfaces, including non-rotationally symmetric surfaces, are increasingly used in ground- and space-based astronomical instruments. The fabrication of these surfaces with sub-micrometric form accuracy and nanometric surface finish, especially for hard and difficult-to-machine materials, has always been a challenge to the optics industry. To produce ultra-smooth surfaces efficiently without subsurface damage and surface scratches, a novel disc hydrodynamic polishing (DHDP) process is proposed through the combination of elastic emission machining and fluid jet polishing. Firstly, the polishing tool for DHDP was carefully designed and the feasibility of the proposed method was experimentally verified. The liquid film was found to act as a carrier of abrasive grains between the polishing tool and the polished surface. Next, computational fluid dynamics (CFD) was used to study the effects of process parameters on the slurry film flow in DHDP. Finally, preliminary experiments were conducted to verify the CFD simulations. The experimental data reasonably agree with the simulation results, which show that increasing rotational speed has no influence on the film thickness for the polishing tool without grooves, but leads to increased film thickness for the polishing tool with grooves. Moreover, DHDP can efficiently reduce the surface roughness and acquire ultra-smooth surfaces without subsurface damage and scratches.

Model-based self-optimization method for form correction in the computer controlled bonnet polishing of optical freeform surfaces.

Freeform surfaces have become increasingly widespread in the optical systems for enhanced performance and compact lightweight packaging. The geometrical complexity and high precision requirements of optical freeform surfaces for various functional optical applications, has posed great challenges in the design, precision machining, and measurement of these surfaces. This paper presents a model-based self-optimization approach for precision machining and measurement of optical freeform surfaces in the computer controlled bonnet polishing (CCBP) process. To realize the technical feasibility, the process parameters and motion control are accurately performed through modelling and simulation of machining processes, error compensation, and on-machine metrology.