Achieving sub-nanometer roughness on aspheric optical mold by non-contact polishing using damping-clothed tool

The surface quality of optical lenses is highly required in imaging functions. Normally, ultra-precision turning is employed to fabricate the optical lenses. However, ultra-precision turning cannot meet the surface quality demands due to the tool marks. In this study, a new damping-clothed (DC) tool and chemical enhanced non-Newtonian ultrafine (CNNU) slurry for non-contact polishing are proposed to achieve sub-nanometer roughness on aspherical optical molds. A material removal model based on the hydrodynamic pressure and velocity simulation was established to calculate the dwell time in curved surface machining. The formation mechanism of sub-nanometer roughness is clarified. The proposed method and slurry were verified by the experiments in processing NiP alloy aspheric optical mold. After the process, surface roughness Sa achieved 0.54 nm and the form accuracy is less than PV 600 nm.