비구면 광학소자의 초정밀가공 형상정도 향상에 관한 연구

Abstract

Because a diamond turning process includes many fields of research, the complete understanding of the diamond turning process is very difficult. The experimental measurement of tool force is one of the important technology of diamond turning process. There are numerous parameters of the process which affect cutting forces. The effect of those parameters and materials have been studied to enhanced the surface roughness after cutting. It is the major purpose of the measurement of the cutting force to understand the effects of the cutting variables such as the cutting force, the machinability of the workpiece, the process of chip formation, chatter and tool wear as well as materials. In general, the cutting force of diamond turning of soft metals, such as aluminum and copper in an diamond turning machine with the depth of cut of several ㎛, is smaller than that of conventional machining. Diamond turning machines have been used for the processing of surface like a mirror with the control scheme of minimizing shape error. Diamond turning is applied to produce highly precision optical components required not only a high machining accuracy but also a good surface roughness. Thermal image system is a device which can visualize the difference of infrared energy naturally emitted by the imaging object. Aluminum and germanium have been widely used as optical parts such as laser reflector's mirror of thermal image system. The global application of aspheric surfaces will expand rapidly on the electronics, optical components, communications, aerospace, defense, and medical optics devices etc. Especially, F-theta lens is one of the important parts in LSU(Laser scanning unit) because it affects dominantly on the optical performance of LSU. The mold core is the most important device to produce plastic F-theta lens by injection molding method. The results obtained in this thesis are as follows ; First, tool holder system is designed and fabricated to measure cutting forces in diamond turning. This system design includes a 3-component piezo-electric transducer. Initial experiments with tool holder system are accomplished to predicted dynamic characteristics as well as a detailed study of cutting parameters. Tool holder system is modeled by considering the element dividing, materials properties, and boundary conditions using MSC/PATRAN. Mode and frequency analysis of structure are simulated by MSC/NASTRAN, for the purpose of developing the effective design. Many cutting experiments conducted for 6061-T651 aluminum and copper. Test involves investigation of velocity effects, the effects of depth of cut, and feedrate on tool force. Cutting forces generally are increased as increasing the depth of cut of the diamond turning process. Second, thermal-imaged Al flat mirror and Ge aspheric lens are fabricated using diamond turning technology. The particular jigs are designed and fabricated to hold axisymmetric Al flat mirror and Ge aspheric lens. The jigs for Al flat mirror and Ge aspheric lens are machined using diamond turning to improve machining accuracy. Using those jigs, thermal-imaged Al flat mirror and Ge aspheric lens are fabricated. Form accuracy and irregularity of Al flat mirror after machining are 0.835 fringe(at 632.8 nm) and 0.370 fringe(at 632.8 nm), respectively. Surface roughness of Al flat mirror is 0.025 ㎛ Ra. Moreover, form accuracy of Ge aspheric lens after machining is 0.24 ㎛ P-V and surface roughness is 0.0038 ㎛ Ra. Third, mold core for F-theta lens machined to produce plastic F-theta lens. Because F-theta lens is non-axisymmetric surface, the mold core for F-theta lens is machined by fly cutting method using non-axisymmetric aspheric generator. To improve the form accuracy, the mold core for F-theta lens is machined by compensating the center error and the tool radius error. Plastic F-theta lens is produced by injection molding method using the mold core for F-theta lens. Form accuracy of mold core after machining is 0.179 ㎛ P-V(x-axis) and 0.184 ㎛ P-V(y-axis), respectively. In the plastic F-theta lens fabricated by injection molding, form accuracy is 0.2269 ㎛ P-V(x-axis) and 0.165 ㎛ P-V(y-axis). It shows that F-theta lens injected by the fabricated mold core is satisfied to apply for the actual specification.