• 한국정밀공학회지
• /
• 제20권12호
• /
• pp.191-197
• /
• 2003

As mechanical components are miniaturized, the demand on micro die and mold is increasing. Micro mechanical components usually have high hardness and good conductivity. So micro electrical discharge machining (MEDM) is an effective way to machine those components. In micro cavity fabrication using MEDM, it is observed that the bottom surface of cavity is distorted. Electric charges tend to be concentrated at the sharp edge. At the center of the bottom surface, debris can not be drawn off easily. These two phenomena make the bottom surface of the electrode and workpiece distort. As machining depth increases, the distorted shape of electrode approaches hemisphere. This process is affected by capacitance and the size of electrode. By using a smaller electrode than the desired cavity size and appropriate tool movement, bottom shape distortion can be prevented.

• International Journal of Precision Engineering and Manufacturing
• /
• 제6권4호
• /
• pp.44-48
• /
• 2005

As mechanical components are miniaturized, the demands on micro die/mold are increasing. Micro mechanical components usually have high hardness and good conductivity. Micro electrical discharge machining (MEDM) can thus be an effective way to machine those components. In micro cavity fabrication using MEDM, it is observed that the bottom surface of the cavity is distorted. Electric charges tend to be concentrated at the sharp edge, and debris cannot be drawn off easily at the center of the bottom surface. These two phenomena make the bottom surface of electrode and workpiece distort. As machining depth increases, the distorted shape of the electrode approaches hemisphere. This process is affected by both capacitance and the size of electrode. By using a smaller electrode than the desired cavity size and appropriate tool movement, bottom shape distortion can be prevented.

• Design & Manufacturing
• /
• 제6권1호
• /
• pp.63-66
• /
• 2012

In the manufacturing of a LCD TV bottom chassis, the distortion after forming should be suppressed below pre-defined amount to avoid contact with electric components. Finite element analysis procedure of forming and springback of a LCD TV bottom chassis is developed to investigate the distortion behaviour. It is shown that after the first forming large distortion occur due to uneven metal flow induced by various embossings. In the second forming, distortion is decreased by introducing bead that absorbs the excessive metal flow. It is proved that analysis method could describe these behaviour effectively. The developed analysis method can be used to find the proper location and shape of bead more quickly and effectively.

• 한국전기전자재료학회논문지
• /
• 제18권5호
• /
• pp.389-395
• /
• 2005

The etching technology of the high aspect ratio contact(HARC) is necessary at the critical contact processes of semiconductor devices. Etching the $SiO_{2}$ contact hole with the sub-micron design rule in manufacturing VLSI devices, the unexpected phenomenon of 'profile tilting' or 'bottom distortion' is often observed. This makes a short circuit between neighboring contact holes, which causes to drop seriously the device yield. As the aspect ratio of contact holes increases, the high C/F ratio gases, $C_{4}F_{6}$, $C_{4}F_{8}$ and $C_{5}F_{8}$, become widely used in order to minimize the mask layer loss during the etching process. These gases provide abundant fluorocarbon polymer as well as high selectivity to the mask layer, and the polymer with high sticking yield accumulates at the top-wall of the contact hole. During the etch process, many electrons are accumulated around the asymmetric hole mouth to distort the electric field, and this distorts the ion trajectory arriving at the hole bottom. These ions with the distorted trajectory induce the deformation of the hole bottom, which is called 'profile tilting' or 'bottom distortion'. To prevent this phenomenon, three methods are suggested here. 1) Using lower C/F ratio gases, $CF_{4}$ or $C_{3}F_{8}$, the amount of the Polymer at the hole mouth is reduced to minimize the asymmetry of the hole top. 2) The number of the neighboring holes with equal distance is maximized to get the more symmetry of the oxygen distribution around the hole. 3) The dual frequency plasma source is used to release the excessive charge build-up at the hole mouth. From the suggested methods, we have obtained the nearly circular hole bottom, which Implies that the ion trajectory Incident on the hole bottom is symmetry.

• Journal of Welding and Joining
• /
• 제32권1호
• /
• pp.79-86
• /
• 2014

The purpose of this study is to determine the proper fillet weld size for the stiffeners on hull bottom plate of crude oil tanker. To achieve it, the effective notch stress and hot spot stress of the fillet weld with leg length specified in the rule were evaluated by using comprehensive FE analyses. Based on the results, the fatigue damages at each location of weld were calculated. Meanwhile the transitional behavior of initial welding distortion in the hull bottom plate under the design conditions was investigated by using a non-linear FEA. Welding distortion and residual stress introduced during fabrication process were considered as initial imperfections. According to FE analysis results, if the fillet leg length satisfies the design criteria of the classification society, the concern on the root failure at the fillet welds in the bottom hull plate during the design life can be negligible. In addition, considering the transitional behavior of the distortion during the service life, the fillet leg length should be minimized.

• 한국공작기계학회논문집
• /
• 제15권3호
• /
• pp.32-38
• /
• 2006

During stereolithography processes, the shape errors such as curl distortion and distortion of side face are generated due to the shrinkage of liquid resins. In this study, the effects of dimension of part and structure of supports on the shape error are examined. Cubic specimens which have different thicknesses are manufactured and their deformations are measured with CMM. Thicker part generates smaller curl distortion of top face and larger of bottom face. Also thicker part generates larger distortion of side face until part thickness increases to about 20mm. Larger stiffness of supports which is obtained by shorter spacing of the supports and line type contact instead of point type contact generates smaller shape error of the part.

• Fisheries and Aquatic Sciences
• /
• 제15권4호
• /
• pp.337-343
• /
• 2012

The Korean bottom trawl survey was conducted using a trawl designed by the National Fisheries Research and Development Institute (NFRDI). The capture efficiency and size selectivity of this trawl for snow crab Chionoecetes opilio was investigated by experimental tows. An auxiliary sampling net (underbag) was attached beneath the trawl net to capture crabs escaping under the trawl footrope. Experimental tows were made by the same vessel speed (3.4 knots) as in the bottom trawl survey, but toing time was shortened from the standard 30 min to 10 min to reduce possible trawl distortion due to the high catch rate of mud and debris in the underbag. In averaged over 17 tows conducted between 110-383 m depth, trawl efficiency of both males and females combined increased from about 10% at 20 mm (carapace width) to about 70% at 100 mm, with a width of 50% capture equal to 78 mm.

• 디지털콘텐츠학회 논문지
• /
• 제12권1호
• /
• pp.49-55
• /
• 2011

비 자성 금속 screw를 이용한 고정술을 시행한 환자를 대상으로 검사하는 자기공명영상에서는 자장의 기하학적 변형을 일으켜 영상에 자화율 인공물을 유발시킨다. 이에 본 연구에서는 자화율 인공물 발생 시 주파수 경사 방향 변환에 따른 영상의 왜곡 정도를 비교, 확인하고자 하였다. 우선 티타늄 성분의 비 자성 금속 screw을 삽입한 자체 팬텀을 제작하여 관심영역을 설정하고 주파수 경사 방향을 축상면에서는 전측-후측을 우측-좌측 방향으로 변환하였고 관상면에서는 우측-좌측을 위측-아래측으로 변환하였고 시상면에서는 상측-하측을 전측-후측으로 변환하여 관심영역의 왜곡 정도를 비교, 관찰 하였다. 결과적으로 주파수 경사 방향을 변환 하였을 때 관심 영역의 왜곡차이를 확인 할 수 있으며 향후 경사 방향을 적절하게 변경함으로써 진단적 효율을 높일 수 있을 것으로 사료된다.

• 한국표면공학회지
• /
• 제53권5호
• /
• pp.227-231
• /
• 2020

This article investigated the effects of stainless steel plate-patterns bonded to aluminum frypan on the thermal distortion and surface temperature of the frypan during gas or induction heating. Two different stainless steel plate-patterns were employed: type A contains only circular holes and type B has not only circular holes but also vacant spaces of 0.5 mm thick and 40 mm long straight line crossing 60 mm long curved line. The bottom of the frypan was distorted during heating when type A stainless steel plate-bonded frypan while no significant thermal distortion was observed for type B stainless steel plate-bonded frypan during heating. Temperature of the frypan surface showed the same trend during gas heating, irrespective of stainless steel plate-patterns. During induction heating, however, the frypan with type B stainless steel plate-pattern showed lower surface temperature than the frypan with type A stainless steel plate-pattern. It is concluded that Type B stainless steel plate-pattern with circular holes and vacant spaces of lines is very effective for minimizing a thermal distortion and lowering the surface temperature of an aluminum frypan during induction heating.

• Structural Engineering and Mechanics
• /
• 제4권1호
• /
• pp.37-47
• /
• 1996

The paper considers the elastic distortional buckling of overhanging beams, which consist of an internal segment with a cantilevered segment continuous over an internal support. The beams were considered loaded by a concentrated load at the cantilever tip, and the beams were either partially restrained or laterally restrained over the internal support. An efficient line-type finite element developed previously by the author was modified to incorporate loading remote from the shear centre, as well as to allow for lateral buckling without distortion. Buckling loads were obtained for a range of geometry when the load was placed on the top flange, at the shear centre or on the bottom flange. Buckling mode shapes were also obtained, and conclusions drawn regarding the influence of distortion on the overall buckling load.