• 한국정밀공학회지
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• 제21권6호
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• pp.43-51
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• 2004

A method for form error prediction in side wall machining with a flat end mill is suggested. Form error is predicted directly from the tool deflection without surface generation by cutting edge locus with time simulation. Developed model can predict the surface form error about three hundred times faster than the previous method. Cutting forces and tool deflection are calculated considering tool geometry, tool setting error and machine tool stiffness. The characteristics and the difference of generated surface shape in up milling and down milling are discussed. The usefulness of the presented method is verified from a set of experiments under various cutting conditions generally used in die and mold manufacturing. This study contributes to real time surface shape estimation and cutting process planning for the improvement of form accuracy.

• 한국재료학회지
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• 제6권1호
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• pp.67-78
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• 1996

제 3원소가 첨가된 금속간 화합물 TiAI 금속간 화합물 분말을 PREP법(플라즈마 회전전극법)으로 제조하여, 통.방전 강압소결법에 의해 치밀한 소결체를 만들었다. 이에 대해 첨가 원소의 종류와 열처리에 따른 고온 및 상온 압축 특성의 변화를 조사하였다. 소결체의 미세조직은 ${\gamma}$/$\alpha$2 lamella로 이루어진 완전 변태구조였고, 결정립의 크기는 140-150$\mu\textrm{m}$였으며 계단형 결정립계를 나타내었다. 소결체를 ($\alpha$+${\gamma}$)구역인 130$0^{\circ}C$에서 2시간 동안 열처리한 결과, 모든 조성의 시편이 등축점 ${\gamma}$와 lamella로 이루어진 전형적인 duplexrn조로 변태하였다. 상온 압축 시험에서 시편은 파괴될 때까지 가공경화 현상이 나타났으며, Cr을 첨가한 시편이 가장 큰 파괴응력과 변형률을 나타내었다. 한편, 고온 압축 시험의 경우 온도상승 때문에 가공경화의 속도가 감소되었고, 80$0^{\circ}C$에서는 가공경화와 회복이 균형을 이루는 소위 정상 상태의 변형을 보였다.

• 한국정밀공학회지
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• 제16권2호통권95호
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• pp.123-129
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• 1999

Ball-end milling process is widely used in the die and mold manufacturing because of suitable one for the machining of free-form surface. During the process, the pencil cutting operation can be adopted before finish cut to eliminate overload in uncut area caused by large diameter of ball-end mill. The ball-end mill cutter for the pencil cutting is easily deflected by cutting force due to the long and thin shape, and the tool deflection in pencil cutting is one of the main reason of the machining errors in a free-form surface. The purpose of this study is to find the characteristics of deflected cutter trajectory by constructing measurement system with eddy-current sensor. It was found that the severe reduction of corner radius produced the overcut during the plane cutting. Up cutting method induced the overcut both plane and slope cutting, but down cutting one induced the undercut. From the experiments, down cutting with upward cutting path can generate the small undercut surface.

• 한국공작기계학회논문집
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• 제10권4호
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• pp.55-64
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• 2001

In this study, hemisphere and cylindrical shapes were machined for different tool paths and machining conditions with ball endmill cutters. Tool deflection, cutting forces and shape accuracy were measured according to the inclination position of the sculptured surface. As the decreasing of inclination position angle, the tool deflection was increased due to the decreased cutting speed when the cutting edge is approaching toward the center. Tool deflection when upward cutting is obtained less than that of downward cutting and down-milling in upward cutting showed the least tool deflection for the sculptured surface. Roundness values were found in least roundness error when down-milling in upward cutting. It is obtained the very little difference between 90。and 45。 of inclination position angle. The best surface roughness value was obtained in upward up-milling and showed different tendency with tool deflection and cutting force. For down-milling, the cutting resistance of the side wall direction is larger than that of feed direction. Therefore, this phenomenon which is received over cutting resistance can be caused of chatter.

• 한국공작기계학회논문집
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• 제17권2호
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• pp.128-134
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• 2008

This paper presents a machining error compensation methodology due to deflection of micro cutting tools in side cutting processes. Generally in order to compensate for tool deflection errors it is necessary to carry out a series of simulations, cutting force prediction, tool deflection estimation and compensation method. These can induce numerous calculations and expensive costs. This study proposes an improved approach which can compensate for machining errors without simulation processes concerning prediction of cutting force and tool deflection. Based on SEM images of test cutting specimens, polynomial relationships between machining errors and corrected tool positions were induced. Taking into account changes of cutting conditions caused by tool position variation, an iterative algorithm was applied in order to determine corrected tool position. Experimental works were carried out to validate the proposed approach. Comparing machining errors of nominal cutting with those of compensated cutting, overall machining errors could be remarkably reduced.

• 기계와재료
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• 제23권3호
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• pp.6-14
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• 2011

기존의 소성가공공정에서의 미세조직 예측 기술은 온도 및 외력에 의한 금속학적 변화를 모사하기 위해 다수의 실험에 기반한 경험적 모델링 작업이 요구되고 이를 구현할 수 있는 기계 및 재료적 지식 기반이 동시에 요구되기 때문에 현재까지는 신뢰성을 갖는모델 및 수치해석기술은 충분히 확보되지 못한 상태이다. 이러한 미세조직 예측기술의 정확도를 향상시키고자 하는 일환으로, 최근에는 매크로 스케일의 FE 해석과의 결합을 통해 소성가공공정과 이후의 열처리 공정에서의 정적 재결정 동적 재결정 상변태 변형유기변태 등 복잡한 미세조직 현상을 그 변화가 일어나는 실제 메조 스케일에서 예측하고자 하는 연구가 시도되고 있다. 본고에서는 그 중에서도 소성가공에서 발생하는 재결정 거동 예측에 주로 적용되고 있는 데조스케일 해석 기법과 매크로-메조 다단위 스케일 해석 기법의 국내외 연구 현황에 대해 알아보고자 한다. 또한, 이를 이용한 소성가공공정에서의 미세조직 예측 사례와 미세조직 예측기술의 전망에 대해 기술하고자 한다.

• 한국기계가공학회지
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• 제1권1호
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• pp.5-14
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• 2002

Hemisphere shapes were machined for different tool paths and machining conditions with ball endmill cutters. It was also found out how feedrate affect the precision of the machining and also tried to study the most suitable feedrate in specific cutting condition. Tool deflection, cutting forces and shape accuracy were measured according to the inclination position of the sculptured surface. As the decreasing of inclination position angle, the tool deflection was increased due to the decreased cutting speed when the cutting edge is approaching toward the center. Tool deflection when upward cutting IS obtained less than that of downward cutting and down-milling in upward cutting showed the least tool deflection for the sculptured surface. For down-milling, the cutting resistance of the side wall direction is larger than that of feed direction. It was found that the tool deflection is getting better as tool path is going to far from the center for convex surface.

• 한국기계가공학회지
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• 제11권3호
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• pp.19-23
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• 2012

Glassy carbon is widely used for high temperature melting process such as quartz due to its thermal stability. For utilizing Classy Carbon to glass mold press(GMP) optical lens, brittleness of Glassy Carbon is main obstacle of ultraprecision machining. Thus authors investigated ductile machining of Glassy Carbon adopting turning and grinding process respectively. From the experiments, ultraprecision turning surfaces resulted brittle crack in all machining conditions and ultraprecision grinding surfaces showed semi-ductile mode in small undeformed chip thickness conditions.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1993년도 제1회 학술강연회논문집
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• pp.27-33
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• 1993

천마 연소관 및 Bracket는 고강도 특수강의 일종인 Maraging steel C-250 Grade로서 유동성형공정 (flow forming process: F/F) 및 용접공정을 거쳐 시효경화후의 경도(HRC 48-52)가 높아 절삭가공 및 Tapping에 어려움이 있다고 판단되어 브라켓 밀링가공(Tapping포함)을 시효경화공정 이전에 완성하는 것으로 공정 FLOW를 설정하였으나, 시효경화 시 유동성형공정 잔류응력 및 재질특성에 의한 수축, 변형 등으로 도면상 요구된 품질(형상 및 위치공차) 만족이 미흡하였을 뿐만 아니라 오히려 전체 공정 수만 증가하였음. 따라서 연소관 및 Bracket 완성가공을 시효경화 후에 실시하는 것으로 공정 개선 하고자 시험 작업한 결과, 선삭, 밀링작업등 다른 기계가공 공정의 문제점은 대부분 해결할 수 있었으나, Tapping공정만은 해결할 수 없어서 진정한 공정개선을 기할 수 없었음. 그러나, 제품의 품질 및 생산성을 고려 시효경화 후 Tapping 공정실시 필요성이 강력히 대두되어 Maraging steel 재질특성에 적합한 공구 및 작업조건을 검토, 설정 시험작업 함으로써 공정개선을 이룰 수 있었음.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 추계학술대회 논문요약집
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• pp.271-271
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• 2003