• 소성∙가공
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• 제20권8호
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• pp.581-587
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• 2011

The production of high-precision micro-sized screws, used to fasten parts of micro devices, generally utilizes a cold thread-rolling process and two flat dies to create the teeth. The process is fairly complex, involving parameters such as die shape, die alignment, and other process variables. Thus, up-front finite-element(FE) simulation is often used in the system design procedure. The final goal of this paper is to produce high-precision screw with a diameter of $800{\mu}m$ and a thread pitch of $200{\mu}m$ (M0.8${\times}$P0.2) by a cold thread rolling process. Part I is a first-stage effort, in which FE simulation is used to establish process parameters for thread rolling to produce micro-sized screws with M1.4${\times}$P0.3, which is larger than the ultimate target screw. The material hardening model was first determined through mechanical testing. Numerical simulations were then performed to find the effects of such process parameters as friction between work piece and dies, alignment between dies and material. The final shape and dimensions predicted by simulation were compared with experimental observation.

• Journal of Mechanical Science and Technology
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• 제17권5호
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• pp.668-678
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• 2003

For the purpose to facilitate development of high-speed spindle units (SUs) running on rolling bearings, we have developed a beam element model, algorithms, and software for computer analysis of thermal characteristics of SUs. The thermal model incorporates a model of heat generation in rolling bearings, a model of heat transfer from bearings, and models for estimation of temperature and temperature deformations of SU elements. We have carried out experimental test and made quantitative evaluation of the effect of operation conditions on friction and thermal characteristics of the SUs of grinding and turning machines of typical structures. It is found out that the operation conditions make stronger effect on SU temperatures when rpm increases. A comparison between the results of analysis and experiment proves their good mutual correspondence and allows us to recommend application of the models and software developed for design and research of high-speed SUs running on rolling bearings.

• Design & Manufacturing
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• 제2권4호
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• pp.11-15
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• 2008

In the sheet metal forming using a high speed press machine, driving device, such as crank, link, and knuckle mechanism, has to be designed in consideration of impact at a moment when press die contact with material, because the impact affects a dimensional accuracy of products and a life span of press die. In this study, dynamic analysis was performed using numerical simulation in order to verify the impact reduction effect for proposed double knuckle mechanism by estimating rolling and pitching moment of slide.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.432-435
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• 2005

Extensive width reduction of slabs is an important technology to achieve continuous production between the steelmaking and hot rolling processes. Conventionally, a vertical roll process has been used to achieve extensive width reduction. However, it is impossible to avoid the defects such as dog-bone, fish tail and camber. The deformation behavior in the width sizing process is more favorable than that in conventional vertical rolling edger, i.e. the material better flows toward the center of slab. This study is carried out to investigate the deformation of slab by two-step sizing press. The FE-simulation is utilized to predict plastic deformation mode in compression by a sizing press of slabs far hot rolling. In this paper, the various causes of the asymmetrical rolling phenomena are mentioned for the purpose of understanding of rolling conditions. Analytical results of slab-deformation by sizing press are presented below in this study.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 The 8th Asian Symposium on Precision Forging ASPF
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• pp.107-114
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• 2003

Although cross rolling process has many advantages in forging a joint shaft, an automotive component of front axle unit, subsequent process is necessary to straighten its bending during forging process. In this paper the bending minimization of the joint shaft was studied to eliminate such an additional process. First of all, a characteristic diagram was used to find out factors affecting the bending of the shaft. Also design of experiments was utilized for estimating the influence of those factors. It was found that the phase angle, which is the difference in starting positions between upper and lower dies, was important to minimize the bending of joint shaft and die cooling is necessary to diminish the distribution of bending.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.488-491
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• 2000

Bi-2223/Ag superconducting wires have been mainly prepared by a powder-in-tube method. The drawing and the rolling are main processes to increase the core density and wire length. In the fabrication of long wire, especially, the drawing should be precisely controlled to assure the filament homogeneity. In this paper, the influences of drawing die angle, bearing length and reduction ratio on the sausaging and the critical current density of the wire are investigated. Single cored and multi-filamentary wires are fabricated by PIT method with different conditions. The core densities and sausaging in the wires are investigated and are discussed regarding their relationship to the I$_{c}$. It was made clear that the geometry of drawing die is sensitively dependent on the sausaging. The improvement of I$_{c}$ was achieved by reducing the die angle and high core density.ity.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.276-279
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• 2000

When high temperature superconducting tapes is fabricated using the PIT (Powder In Tube) method, the length of HTS tapes is increased more than 500 ${\sim}$ 1,000 times of initial powder packed billet. On mechanical processing, heterogeneous properties between the ceramic superconducting core and Ag/Ag alloy sheath occur the non-uniformity deformation as like sausaging that deteriorate the critical current properties of HTS tapes. In this study, we investigated the workability of Bi-2223/Ag/Ag alloy sheath tapes fabricated by the PIT method involving a number of different mechanical processes, multi drawing and rolling. In order to obtain the high critical current density and high uniformity of Bi-2223/Ag sheath tapes, the influences of powder packing density, drawing die angle and rolling parameters were studied. We found that the roll diameter is an important variable in the rolling process, as critical current of tapes rolled using 250 mm rolls was higher than that using 150 mm rolls.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.201.1-201.1
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• 2014

본 연구에서는 Slot die coating 공법으로 코팅된 Poly (3-4 ethylenedioxythiophene): Poly (styrenesulfonate) (PEDOT:PSS) 박막과 비정질 ITO 박막의 전기적, 광학적, 기계적 특성을 비교 평가하여 Slot die coating 공법으로 코팅된 PEDOT:PSS 박막의 유기태양전지의 전극으로서의 적용가능성을 확인하였다. 상업용 PEDOT:PSS 박막은 보통 280 Ohm/sq.의 면저항과 가시광 영역에서 약 80%의 광투과도를 나타내며, 비정질 ITO 박막과 유사한 전기적, 광학적 특성을 나타내었다. Slot die coating 공법을 통해 제작된 PEDOT:PSS 투명 전극과 비정질 ITO 투명 전극의 기판 휘어짐에 따른 전기적 안정성을 비교 평가하기 위해 25 mm에서 1 mm까지 radius 변화에 따른 저항의 변화를 측정하였다. 그 결과, 비정질 ITO 투명 전극 대비 PEDOT:PSS 투명 전극이 더 우수한 전기적 안정성을 나타냄을 확인하였다. 또한, 다양한 Bending test (Inner/Outer bending, Rolling, Stretching, Twisting) 를 통해 비정질 ITO 투명 전극 보다 Slot die coating 공법으로 코팅된 PEDOT:PSS 투명 전극의 우수한 기계적 특성을 확인하였다. 이를 바탕으로 Flexible 유기태양전지에의 적용 가능성을 알아보기 위해 Slot die coating 공법으로 코팅된 PEDOT:PSS 투명 전극과 비정질 ITO 투명 전극을 유기태양전지의 anode 층에 적용하여 각각 제작하고 그 특성을 평가하였다. 비정질 ITO 투명 박막을 적용한 유기태양전지 대비 Slot die coating 공법으로 코팅된 PEDOT:PSS 투명 박막으로 제작한 유기태양전지에서 더 높은 효율이 나타났으며, 이로써 Slot die coating 공법으로 코팅된 PEDOT:PSS 투명 전극의 Flexible 유기태양전지로써의 적용 가능성을 확인하였다.

• 대한기계학회논문집A
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• 제40권11호
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• pp.971-978
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• 2016

최근 전자제품의 소형화 및 경량화 추세에 따라 초소형 체결제품의 개발 필요성이 대두되고 있다. 본 연구에서는 이동통신기기 적용을 위한 초소형 나사(외경 1.0 mm 피치 0.25 mm)의 전조공정에 대한 연구를 수행하였으며, 특히 대칭 나사산과 비대칭 나사산의 성형을 위한 전조공정의 유한요소해석을 수행하였다. 유한요소해석을 통해 전조금형의 수평방향 간격, 수직방향 간격, 이동 거리 등의 공정변수가 성형된 나사산의 형상정밀도에 미치는 영향을 분석하였다. 또한 대칭 나사산과 비대칭 나사산에서 발생되는 재료 유동의 차이를 비교하고, 그에 따른 공정변수의 영향을 분석하였다. 상기 해석 결과로부터 도출된 공정변수를 실제 전조공정에 적용한 결과 대칭 나사산과 비대칭 나사산 모두 원하는 형상정밀도 내에서 성공적으로 성형될 수 있음을 확인하였다.

• 대한기계학회논문집A
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• 제39권7호
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• pp.721-727
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• 2015

풍력 발전기용 기계부품은 주로 자유단조 공법을 통하여 제조된다. 본 연구는 풍력발전기용 타워부품인 도아프레임의 제조하기 위한 발전된 단조공법에 관한 연구이다. 개발된 단조공법의 장점은 원소재 회수율을 높임에 따라 원소재 투입량을 줄임으로 제조원가를 낮춘다. 기존의 단조공업은 유압프레스를 이용하여 단조작업이 이루어지며 최종제품과 단조품의 형상 차이로인하여 많은 부분이 가공으로 제거된다. 하지만 제안된 단조공법은 열간 자유단조와 링롤링공법을 통하여 원소재 회수율을 높이게 된다. 새로운 공법의 유효성은 링롤링 블랭크의 치수와 밀접한 관련이 있기 때문에 유한요소해석을 통하여 블랭크의 치수를 최적화 하였다. 유한요소해석을 통하여 얻은 단조품의 치수는 시제품 생산을 통하여 검증하였다.