Finishing of micro-aspheric tungsten carbide mold using small viscoelastic tool

Abstract

Tungsten carbide is widely used as the material of replication mold to produce small aspheric optics, and the polishing process determines the precision of the mold. However, for micro-aspheric tungsten carbide mold, the existing polishing methods are difficult to realize the from error modification during the polishing because the polishing tool is always larger than small mold. Therefore, a polishing tool which using polyester fiber cloth to wrap small-size rigid ball is used in this paper. In order to predict the tool influence function (TIF) of this polishing tool, a series of theoretical analysis and experimental verification are carried out in this paper. Firstly, by analyzing the structural and viscoelastic characteristics of the fiber cloth, the pressure distribution in the polishing contact area is determined. And the polishing speed distribution is obtained by analyzing the kinematic movement of the polishing tool; Then, combined with Preston equation, the tool influence function is derived; Afterward, through a series of single point polishing experiments, it is verified that the volume error between the theoretical removal model and the experimental removal is less than 10.8%; Finally, the tool influence function is applied to the form error corrective polishing of small size symmetric aspheric tungsten carbide mold. After one form error corrective polishing, the PV value (Peak to Valley) of form error is decreased from 0.405um to 0.068um, which verifies the effectiveness of the polishing method of small size tungsten carbide mold in form error correction.