• Proceedings of the KIEE Conference
• /
• 2001.07c
• /
• pp.1349-1351
• /
• 2001

Polycrystalline diamond films are deposited by using a microwave plama CVC system, where the bias-enhanced nucleation (BEN) method is employed. Effects of the varying microwave power, the surface treatment by hydrogen plasma, and the cyclic hydrogen etching during deposition on the crystallinity as well as on the surface roughness of deposited films are examined by Raman spectroscopy, SEM, and AFM. A novel method for achieving a smoother diamond surface is also suggested through the indirect wafer bonding and back-side polishing.

• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.7
• /
• pp.88-96
• /
• 2002

High-speed machining is one of the most effective technologies to improve productivity. Because of the high speed and high feed rate, high-speed machining can give great advantages for the machining of dies and molds. This paper describes on the improvement of machining accuracy in high-speed machining. Depth of cut, feed rate and spindle revolution are control factors. The effect of the control factors on machining accuracy is investigated using two-way factorial design.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.398-398
• /
• 2012

GaN 기반의 InGaN/GaN 다중양자우물(MQW) 구조의 발광다이오드는 다양한 파장대의 가시광을 방출하는 소자로 교통 신호등, 디스플레이, LCD backlight, 일반 조명까지 넓게 응용되고 있다. 그러나, 이러한 응용을 위해서는 전류 주입 효율, 내부양자효율, 광추출 효율을 개선하는 연구를 통한 발광 다이오드의 광효율을 높이는 연구가 필수적이다. 최근 많은 연구 개발에 의해 내부양자효율은 크게 향상 되었지만, 광추출 효율은 GaN (n=2.4)와 공기 (n=1)의 굴절률 차이에 의해 아직까지 낮은 실정이다. 광추출 효율을 개선하기 위해 반사전극, 전방향 반사전극, 표면 거칠기, Chip 성형 등의 기술이 제안되고 있다. 본 연구는 LED의 광추출 효율을 높이기 위해 다양한 모양의 Hydrothermal 법에 의해 성장된 ZnO 나노 구조 및 나노스피어 리소그라피를 통한 폴리스티렌 나노 구체의 주기적인 배열에 따른 특성을 연구하였다.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.16 no.6
• /
• pp.49-54
• /
• 2007

Electropolishing, the anodic dissolution process without contact with tools, is a surface treatment method to make a surface planarization using an electrochemical reaction with low current density. Nitinol is a metal alloy composed of Ni and Ti around 50% respectively which has shape memory effect. Nitinol can be put various applications which require purity and high pricision surface of products. The aim of this study is to investigate the characteristic of electropolishing effect for nitinol workpieces. In order to analyze the characteristics of electropolishing effect, surface roughness and micro-burr size were measured in terms of machining conditions such as current density, machining time and electrode gap. The tendencies about improvement of surface roughness and deburring effect by electropolishing for nitinol workpieces were determined.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.8
• /
• pp.641-647
• /
• 2002

Objectives of this paper are to investigate the effect of roughness of micro-hatching tubes on the absorption performance and to develop on experimental correlation of Nusselt as a function of the roughness. Three different micro-scale hatched tubes and a bare tube were tested in the present experiment. $H_{2}O/LiBr$ solution is used as working fluid. It was found that absorption performance of micro-scale hatched tubes were improved upto 2 times with an error band of ${\pm}25%$ compared with the bare tube. An experimental correlation of Nusselt was developed as a function of the roughness.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.192.1-192.1
• /
• 2013

본 연구는 기존의 Sputtering 방식에 Modulation 방식을 적용한 Modulated Sputtering System (MSS)에 관한 특성 관찰과 이를 이용한 박막 증착 및 분석에 관한 내용이다. MSS에 인가하는 전압은 pulse on 시간동안 타겟에 음의 전압이 인가되어 sputtering에 의한 박막이 증착되고, pulse off 시간동안에는 양의 전압을 인가하여 증착된 박막에 양이온을 입사시켜 에너지 전달에 의한 박막의 특성을 향상시키고 자한다. MSS에 인가되는 전압과 주파수, 그리고 펄스폭을 변화시키며 전압과 전류, 그리고 기판에 입사하는 이온에너지 특성을 관찰하였다. 또한 MSS를 이용하여 티타늄(Ti), 탄소(C), 알루미늄이 도핑된 산화아연(AZO) 박막을 증착하였다. 증착된 박막은 a-step, SEM, XRD, AFM, 4 point probe를 이용하여 박막의 두께, 결정성장면, 표면 거칠기, 비저항 등을 분석하였다. Ti 박막에서는 기판에 입사되는 양이온의 에너지가 증가함에 따라 결정 방위면이 (002)에서 (001)로 변화함을 확인하였고 탄소 박막과 AZO 박막의 경우에는 기판에 입사되는 양이온의 에너지 변화에 따라 박막의 전도도를 조절할 수 있음을 확인하였다.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.16 no.3
• /
• pp.119-124
• /
• 2017

Machining optimization using typical computer-aided manufacturing (CAM) software mainly depends on tool paths, and it is impossible to predict the behavior of material or cutting force. In this paper, cutting force analysis simulation is performed on the Unibody Case of a mobile phone with the aim of optimizing cutting-force-based machining using the Third Wave Systems' AdventEdge Production Module. Machining time after optimization was shortened by 42% for roughing compared to pre-optimization, and actual machining time was reduced by 36.8%. For finishing, machining time was reduced by 92%, and actual machining time was reduced around 90%. A surface roughness analysis found that the post-optimization surface roughness was $1.16{\mu}m$ Ra, compared to a pre-optimization value of $1.75{\mu}m$ Ra.

• Journal of the Korean Society for Precision Engineering
• /
• v.32 no.11
• /
• pp.983-988
• /
• 2015

This paper details a new ultra-precise turning method for increasing surface quality, "Multi Point B Axis Control Method." Machined surface error is minimized by the compensation machining process, but the process leaves residual chip marks and surface roughness. This phenomenon is unavoidable in the diamond turning process using existing machining methods. However, Multi Point B axis control uses a small angle (< $1^{\circ}$) for the unused diamond edge for generation of ultra-fine surfaces; no machining chipping occurs. It is achieved by compensated surface profiling via alignment of the tool radial center on the center of the B axis rotation table. Experimental results show that a diamond turned surface using the Multi Point B axis control method achieved P-V $0.1{\mu}m$ and Ra 1.1nm and these ultra-fine surface qualities are reproducible.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2017.05a
• /
• pp.119.2-119.2
• /
• 2017

무전해 니켈도금은 전기 공급 없이 환원재의 화학반응에 의해 도금이 진행되며, 복잡한 형상의 제품에도 균일한 도금 층을 형성시킬 수 있어 널리 적용되는 기술이다. 특히, 전기 니켈도금 층에 비해 무전해 니켈도금 층의 내식성과 내마모성이 우수하여 산업현장에서 가장 많이 사용되고 있다. 그러나 해양환경에서 빠른 유속 변화에 의해 발생되는 캐비테이션-침식 방지를 위한 무전해 니켈도금의 적용은 전무한 실정이다. 따라서 본 연구에서는 회주철의 캐비테이션-침식 방지를 위해 최적의 무전해 니켈도금 조건을 규명하고, 그 캐비테이션 저항성을 평가하고자 하였다. 무전해 니켈코팅을 위한 모재는 gray cast iron (FC250)을 $19.5mm{\times}19.5mm{\times}5mm$의 크기로 제작하였다. 회주철의 인장강도는 $330N/mm^2$이며, 그 성분 조성(wt.%)은 3.23 C, 1.64 Si, 0.84 Mn, 0.016 P, 0.013 S 그리고 나머지는 Fe이다. 시험편은 SiC 페이퍼 grit #1200까지 연마하였으며, 시험편의 표면 거칠기(centre line average, Ra)는 $1.6-2.1{\mu}m$ 범위 내로 제작하였다. 연마된 시험편은 증류수(distilled water) 세척 후 hot air로 건조하였다. 무전해 도금 전 시험편은 탈지를 위해 아세톤 용액(room temperature, RT)에서 3분간 초음파 세척하고, $90^{\circ}C$의 알카리 수용액으로 5분간 세척하였다. 그리고 표면활성화를 위한 산세척(acid pickling)은 5% sulfuric acid 용액에서 30초 동안 실시하였다. 무전해 Ni-P(electroless nickel, EN) 도금 전과 모든 과정마다 증류수로 시험편을 철저하게 세척하였다. EN 도금을 위한 도금욕(the bath)은 기존 문헌 연구를 통해 조성성분, 도금조건 및 변수들(the parameters)의 적절한 범위를 결정하였다. 도금조로 500mL 비커를 사용하였으며, 모든 시험편은 2시간 동안 EN deposition을 실시하였다. 캐비테이션 실험 결과 EN 도금의 표면경도가 증가함에 따라 캐비테이션 저항성도 현저하게 향상되었다.

• Korean Journal of Metals and Materials
• /
• v.46 no.3
• /
• pp.169-173
• /
• 2008

Characteristics of etching and induced surface morphology variation by wet-etching of n-type GaN were investigated using phosphoric acidic solutions. Generally, the etch-rate was increased as the temperature of the etch solutions was increased, and the highest etch rate of about $300{\AA}/min$ was achieved at the temperature of $180^{\circ}C$. The morphology variation of the etched surface was observed by optical microscopy and atomic force microscopy. Initially, high density of hexagonal holes or pits were formed on the etched surface at the time of 40 min with the bimodal size of $20{\mu}m$ or $5{\mu}m$, respectively. However, as the etching time was increased further, the lateral size of the hexagonal holes or pits was increased, and finally, joined and merged together at the time of 100 min. This means that the etching of n-type GaN by phosphoric acidic solutions proceeded through the lateral widening and the merging of initial holes and pits.