• 한국기계가공학회지
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• 제14권3호
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• pp.36-42
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• 2015

The aspherical lens was designed to be able to array a focal point. For this reason, it has very curved surface. The aspherical lens is fabricated by injection molding or diamond turning machine. With the aspherical lens, tool marks and surface roughness affect the optical characteristics, such as transmissivity. However, it is difficult to polish free form surface shapes uniformly with conventional methods. Therefore, in this paper, the ultra-precision polishing method with MR fluid was used to polish an aspherical lens with 4-axis position control systems. A Tool path and polishing mechanism were developed to polish the aspherical lens shape. An MR polishing experiment was performed using a generated tool path with a PMMA aspherical lens after the turning process. As a result, surface roughness was improved from $R_a=40.99nm$, $R_{max}=357.1nm$ to $R_a=4.54nm$, $R_{max}=35.72nm$. Finally, the MR polishing system can be applied to the finishing process of fabrication of the aspherical lens.

• 한국정밀공학회지
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• 제23권1호
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• pp.97-104
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• 2006

ELID(Electrolytic In-process Dressing) grinding is an excellent technique for mirror grinding of various advanced metallic or nonmetallic materials. A polishing process is also required for elimination of scratches present on ELID grinded surfaces. MAP(Magnetic Assisted Polishing) has been used as polishing method due to its high polishing efficiency and to its resulting in a superior surface quality. This study is describing an effective fabrication method combining ELID and MAP of nano-precision mirror grinding for glass-lens molding mould. It also presents some techniques for achieving the nanometer roughness of the hard metals, such as WC-Co, which are extensively used in precision tooling material.

• 소성∙가공
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• 제21권2호
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• pp.138-143
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• 2012

A polishing method using magnetorheological (MR) fluid has been developed as a new precision technique to obtain a fine surface. The process uses a MR fluid that consists of magnetic carbonyl iron (CI) particles, nonmagnetic polishing abrasives, water and stabilizers. But the CI particles in MR fluids cause a severe corrosion problem. When coated with Xanthan gum, the CI particles showed long-term stability in corrosive aqueous environment. The surface roughness obtained from the MR polishing process was evaluated. A series of experiments were performed on fused silica glass using prepared slurries and various process conditions, including different polishing times. Outstanding surface roughness of Ra=2.27nm was obtained on the fused silica glass. The present polishing method could be used to produce ultra-precision micro parts.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.324-328
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• 2003

The Magnetoeheological fluid has the properties that it's viscosity has dramastic changed under some magnetic fields therefore, Magnetorhlogical fluids has been used for micro polishing of the micro part( for example, a aspherical surface in a micro lens). The polishing process may appears as follows. A part rotating on the spindle is brought into contact with an Magnetorhological finshing(MRF) fluids which is set in motion by the moving wall. In the region where the part and the MRF fulid ate brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. Resonable calculated and experimental magnitudes of the material removal rate f3r glass polishing lends support the validity of the approach.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.98-102
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• 1994

There are many difficulties in automatic polishing for die & mold surfaces. Even though the process has been studied in the past 15 years, it has not been achieved yet, but by the process of actual hand work of well-skilled workers. A new magentic assisted polishing process, which is one of the potential method for automation of surface finishing has been studied in the past 10 years by colleagues. The process has many merits, but on the other hand also has demerits, one being low efficiency of gridability by comparision with grinding wheel polish. Therefore, some attempts were tried to improve the grindability by adopting electropolishing, ultra-high speed milling, 5-axis controlled machine etc... most recently by collegues. This study also aims to improve the efficiency of polishing by introducing the easily-polished shape surface milling method equalizing the tool feed per tooth to the pick feed. This milling method was experimentally confirmed to have sufficient grindability to polish milled surface (with 10 .mu. mRmax surface roughness) into mirror surface (with 0.4 .mu. mRmax surface roughness).

• 한국정밀공학회지
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• 제21권7호
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• pp.46-52
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• 2004

The Magnetorheological fluid has the properties that its viscosity has drastic changed under some magnetic fields therefore, Magnetorheological fluids has been used fur micro polishing of the micro part(for example, a spherical surface in a micro lens). The polishing process may appears as follows. A part rotating on the spindle is brought into contact with an Magnetorheological finishing(MRF) fluids which is set in motion by the moving wall. In the region where the part and the MRF fluid are brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. Resonable calculated and experimental magnitudes of the material removal rate for glass polishing lends support the validity of the approach.

• 한국기계가공학회지
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• 제13권1호
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• pp.92-99
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• 2014

An aspherical lens, which resolves several problems with a spherical lens,typically serves asa key part of an optical system. Generally, an aspherical lens is fabricated using a diamond turning machine or by mean of injection molding. However, residual stress and/or tool marks can arise when using a commercial fabricating method such as DTM or injection molding. A polishing process, thus, is commonly used to obtain a high-precision aspherical lens. In this study, a polishing method using MR fluid was applied to minimize several problems, in this case residual stress and the creation of tool marks, during the cutting process. The MR polishing system was developed to polish aspherical lenses. A series of experiments were performed to obtain a very fine surface roughness. PMMA (the lens material for molding) was used as a workpiece, and the gap size, magnetic field intensity, wheel speed and feed rate were selected as the parameters in this study. Finally, a very fine surface roughness of Ra=2.12nm was obtained after MR polishing.

• 한국기계가공학회지
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• 제16권5호
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• pp.85-90
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• 2017

Mica-glass ceramics has features such as micro-sized crystals, high strength, chemical resistance, semitransparent optical properties, etc. Due to its superior material properties, mica glass ceramics have increasing applications in dental and medical components, insulation boards, chemical devices, etc. In many applications, especially for dental and medical components, ultra-precise polishing is required. However, it is known to be a very difficult-to-grind material because of its high hardness and brittle properties. Thus, in this study, a newly developed ultra-precise polishing method is applied to obtain nano-level surface roughness of the mica glass ceramics using magnetorheological (MR) fluids and nano abrasives. Nano-sized ceria particles were used for the polishing of the mica glass ceramics. A series of experiments were performed under various polishing conditions, and the results were analyzed. A very fine surface roughness of Ra=6.127 nm could be obtained.

• 한국산학기술학회논문지
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• 제16권3호
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• pp.1620-1625
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• 2015

본 연구에서는 산업현장에서 각종 기어나, 축, 체인, 롤러, 금형, 자동차강판 등으로 널리 쓰여 지는 기계구조용 탄소강인 SM45C를 실험소재로 사용하였다. 실험에 사용되는 시험편 표면에 표면경화를 수행하기 위하여 #200 ~ #1500의 순서대로 미세연마 후 거친연마의 연마가공을 실시하였으며, 다이오드 레이저의 표면경화 열처리 후에 자기냉각효과를 고려하여 $100{\times}50{\times}10$의 판재로 시험편을 제작하여 실험하였다. 소재 표면에 다이오드 레이저를 이용하여 국소부위에 표면경화 열처리를 수행하였다. 이때 다이오드 레이저의 출력과 이송속도를 공정조건으로 하여, 미세경도시험, 미세조직시험, 전자 주사 현미경(SEM), 입열량을 분석하였다. 분석 후에는 실험소재의 기계적 특성을 비교하여, 타 표면 경화법에 비해 다이오드 레이저를 이용하였을 때의 표면경화 열처리 신뢰성과 우수함 그리고 최적의 공정조건을 도출하였다. 열처리 후 경화부는 판상 마르텐사이트로 경화 되었으며. 경도값은 Hv729.5로 열처리 후 약 2.3배 이상 표면경도가 향상되있는 것을 확인하였다.

• 광학세계
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• 통권143호
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• pp.30-45
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• 2013

미국 QED Technologies(이하 QED)가 세계 최초로 상용화한 자기유동유체연마장치(이하 MRF$^{(R)}$-Magnetorheological (Fluid) Finishing)는 역시 QED가 개발한 간섭계 응용장비인 SSI$^{(R)}$(Subaperture stitching interferometer)와 같이 운용하면 1um 이하의 나노광학산업에서 ${\lambda}/10$ 또는 ${\lambda}/100$ 이상 더 정밀한 영역을 손 쉽게 제조할 수 있는 획기적인 공정을 가능하게 한다. 이러한 능력 때문에 미국, 유럽 및 일본 등의 첨단광학회사들은 96년 상업화된 이후 MRF$^{(R)}$와 SSI$^{(R)}$ 공정을 앞다투어 도입하며 기존공정이 지니고 있던 많은 한계들을 극복했다. 우리나라의 MRF와 SSI의 도입은 선진국에 비해 10년 이상 늦어진 2008년에 이르러서야 최초의 장비가 도입되었으며 이후 꾸준히 그 응용분야가 확장되어 가고 있다. 2012년에는 한국천문연구원과 그린광학에 SSI의 최신장비인 ASI(Aspheric Stitching Interferometer)와 MRF가 각각 도입됐다. 이를 계기로 해서 한국사무소에서 제안을 하여 QED사의 총괄대표이사인 Dr. Andrew Kulawiec, 응용기술부장인 Paul Dumas, QED 한국사무소의 오한석 박사와 신지식 박사가 그간의 기술동향을 발표하는 기술강연회가 지난 2012년 10월 23일 개최되었다. 한국천문연구원, 그린광학과 한국광학기기산업협회의 후원으로 한국천문연구원 은하수홀에서 개최된 이번 강연회에서는 다음과 같은 세가지 주제를 다루었다. 1. MRF의 원리 및 응용분야의 현황과 장비개발 현황 2. SSI의 원리 및 응용분야의 현황과 장비개발 현황 3. 광학설계와 가공실현성에 도움이 되는 비구면을 표현하는 새로운 식 Q-Polynominal 이번 강연회는 특히 QED의 공정 및 장비개발자들이 직접 참가한 기술강연회로 지난 2004년 및 2008년에 열린 기술강연회와 차별화되며, 25개 업체 약 50여 명이 참석하여 성황리에 마무리되었다. 향후 국내의 사용자 그룹에 대한 세미나를 정기적으로 개최해 QED의 첨단광학기술에 대한 정보교환의 장을 확대할 예정이며, 기술강연회도 가능한 한 정기화할 예정이다. 이번 강연회의 주제 중 우선 MRF와 SSI에 대한 논의를 광학세계 1월호에 소개하고자 한다.