Mr. Min Woo Jeon Profile

Min Woo Jeon

Engineer at Korea Basic Science Institute

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Publications (3)

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PROCEEDINGS ARTICLE | October 16, 2017

Study on a magneto-rheological removal process of periodic turning marks

Proc. SPIE. 10448, Optifab 2017

KEYWORDS: Single point diamond turning, Polishing, Nickel, Surface roughness, Magnetorheological finishing, Surface finishing

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Single Point Diamond Turning (SPDT) has the potential to cost-effectively manufacture optical materials such as metals and plastic types. However, SPDT generally leaves tool marks on the machined surfaces, which creates problems that can deteriorate the optical performance. Several processes have been studied to eliminate the tool marks caused by SPDT, but it was difficult to carry out without the additional defects like sub-surface damages and other tool marks. To overcome this weakness, we investigated the Magneto-Rheological Finishing (MRF) process to effectively remove the periodic micro structures without surface deterioration for optical performance. The workpiece used in the experiment is a mirror plated with electroless nickel-phosphorus. Through the processing of the SPDT, an initial surface gets periodic tool marks, which have a height of 1.1 μm and a pitch of 20 μm. We studied on the reduction rate of the turning marks by the MRF process with some different conditions of uniform removal. The quantitative analysis of the surface roughness and residual marks was performed using a scanning low-coherence interferometer and through the Power Spectral Density (PSD) respectively. The results showed that reduction rates of tool marks depend on the angles (0, 45, and 90 degs) between the turning direction of the tool marks and the rotation direction of MR wheel. In the case of 45 degs, it indicated the fastest reduction rate.

PROCEEDINGS ARTICLE | August 23, 2017

Removal of diamond turning marks with magneto-rheological finishing

Proc. SPIE. 10371, Optomechanical Engineering 2017

KEYWORDS: Mirrors, Diamond turning, Single point diamond turning, Polishing, Diamond machining, Surface roughness, Freeform optics, Magnetorheological finishing, Off axis mirrors, Surface finishing

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A magneto-rheological finishing (MRF) process for the post-treatment of diamond turning is presented to remove the periodic micro structures and sub-surface damages with improvement of the original figure and surface roughness. An off-axis aspherical mirror with electro-less nickel-phosphorus plated surface was machined by a Single point diamond turning machine (SPDTM) and MRF polisher. The machined surfaces were examined by a scanning low-coherence interferometer, and the technique of Fast Fourier Transformation (FFT) and Power Spectrum Density (PSD) were introduced to evaluate the residual diamond turning marks on the turned and polished surfaces. The turning marks, which was clearly visible on the diamond turned surface, were absolutely removed after MR process, and the surface roughness of the machined surface was improved from 6 nm(Sa) and 7 nm (Sq) to 2 nm(Sa) and 3 nm (Sq). Consequently, the experimental results indicate that MRF is suitable for removing periodic micro-patterns caused by diamond turning process with the progress of the original figure and surface roughness.

PROCEEDINGS ARTICLE | October 12, 2015

Ultra precision machining technique of off-axis optics for coastal water remote sensing

Proc. SPIE. 9633, Optifab 2015

KEYWORDS: Fabrication, Mirrors, Diamond machining, Sensors, Remote sensing, Surface roughness, Ocean optics, Aspheric optics, Radium, Off axis mirrors

Read Abstract

An off-axis optical system can effectively avoid some problems, such as aberrations, shielded area created by the secondary mirror and a narrow field of view (FOV), while an on-axis optical system has the problems. Inspired by the consideration, the off-axis optical system is generally used for hyperspectral sensors and telescopes. However, there are several obstacles limiting the productivity of the off-axis optics in fabrication and measurement processes. In this study, to overcome this weakness, we suggests a new fabrication technique using a customized jig, not separated from the work-piece. A convex aspheric mirror and the off-axis mirror are fabricated by Single Point Diamond Turning Machine (SPDTM) for comparison analysis of surface state. The mirrors are made from aluminum (Al6061-T6) and used for the reflectors of a coastal water remote sensing system. We show fast machining and simple measurement in comparison with traditional off-axis single machining and measurement, provide performance results, such as form accuracy and surface roughness measured by both contact 3D profilometer (UA3P) and non-contact 3D profiler (CCI-Optics). The customized ultra-precision machining process can be effectively used for complex off-axis mirror fabricating.

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