非球面 Glass렌즈 성형용 금형코어의 초정밀 硏削加工에 관한 연구

Abstract

Recently, with increasing lightness and miniaturization of high resolution camera phones, the demand for aspheric glass lens has increased because plastic and spherical lenses are unable to satisfy the required performance. Since an aspheric glass lens is fabricated by high temperature and pressure molding using a tungsten carbide molding core, precision grinding and coating technology for the molding core surface is required. Diamond Like Carbon(DLC) and Rhenium-Iridium(Re-Ir) coating are being researched in various fields because of its high hardness, high elasticity, high durability, and chemical stability and is used extensively in several industrial fields. Especially, the DLC and Re-Ir coating of the molding core surface in the molding core used in the fabrication of a glass lens is an important technical field, which affects the improvement of the demolding performance between the lens and molding core during the molding process and the molding core lifetime. In this paper, the optimal grinding condition for tungsten carbide(WC) using DOE(Design of Experiment) for the glass lens molding core is proposed. In addition, feedrate control for influence of surface roughness(Ra) was developed. With the use of the feedrate control method, the surface roughness(Ra) of the molding core was improved by about 1.5 nm(@clear aperture; 3.0 mm). For the 3 mega pixel and 2.5 magnifications optical zoom for camara phone module, tungsten carbide molding cores were fabricated under this optimal grinding condition using feedrate control method. The measurement results of the molding core for DLC coating were as follows: PV of 0.155 ㎛(apheric surface), PV of 0.100 ㎛(plane surface), and Ra of 3.4 nm(aspheric surface) and 1.9 nm(plane surface). The measurement results of the molding core for DLC coating were as follows: PV of 0.153 ㎛(apheric surface), PV of 0.105 ㎛(plane surface), and Ra of 3.5 nm(aspheric surface) and 2.0 nm(plane surface). Molding cores were coated with the DLC and Re-Ir, respectively. Then form accuracy(PV) and surface roughness(Ra) of the cores were measured and evaluated. DLC and Re-Ir coating on the surface of the tungsten carbide molding core can be used not only to improve the demolding performance between the molding core and glass lens and to improve the molding core lifetime, but also to influence the form accuracy and surface roughness of the glass lens. Because SiC is a material of high hardness and high brittleness, it can crack or chip during grinding. It is, however, widely used in many fields because of its superior mechanical properties. In particular, when aspheric glass lens molding core is used, the SiC coating process, which must be carried out before the DLC coating, can be eliminated and thus, manufacturing time and cost can be reduced In this paper, the optimal grinding condition for silicon carbide(SiC) was developed under the grinding condition of tungsten carbide. A silicon carbide molding core was fabricated under this optimal grinding condition using the feedrate control method. The measurement results of the molding core were as follows: PV of 0.260 ㎛(apheric surface) and Ra of 5.3 nm(aspheric surface).