• 한국기계가공학회지
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• 제10권4호
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• pp.121-126
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• 2011

An accumulator placed on the refrigerant cycle pipe lines is a part to relax fluctuations of pressure within the pipe lines and stabilize refrigerants flowed into pipe. The accumulator has been mainly manufactured by the process of tube spinning using CNC(Computer Numerical Control) lathe. However, this process has the defects which are low productivity per hour and high cost. For that reason, tube end-forming using roll die is actively being developed, recently. The purpose of this study is to develope the tube end-forming process using roll die in order to manufacture the accumulator for the refrigeration pipe lines. First, the process design of tube end-forming was performed based on specification of product, and then was verified with FE analysis. Also, the effects of friction coefficient and revolution speed of roll die on forming load were investigated. The analytical results were applied in the final process design of tube end-forming. Finally, tube end-forming test was carried out to verify the validity of the FE analysis and the process design.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.77-82
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• 2003

In end milling process, undeformed chip thickness and cutting force vary periodically with phase change of the tool. Recently, a model has been proposed to simulate the shear and friction characteristics of an up-end milling process in terms of the equivalent oblique cutting to this. In the current study, the varying undeformed chip thickness and the cutting forces in a down-end milling process have been replaced with the equivalent ones of oblique cutting. And, the down-end milling characteristics of SM45C has been compared with that of the up-end milling previously presented with different helix angles.

• 유공압시스템학회논문집
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• 제2권4호
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• pp.23-29
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• 2005

In order to improve the efficiency of hydraulic gear pumps or motors especially for high operating pressure, power losses due to viscous friction and leak flow through gear teeth end-gaps are considered in this paper. Optimal gaps minimizing the power loss for pumps and motors with uniform heights of gaps are analysed first. And the effect of the shapes of gaps with unequal heights on the power loss are studied and discussed by simulation. Considering that the outer shell lacing gear teeth may expand due to high internal pressure or thermal stress, the results drawn in this paper can be used for the design of high efficiency pumps and motors.

• 소성∙가공
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• 제3권1호
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• pp.63-83
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• 1994

In this paper, the slab method have been applied to investigate the strip casting process in which hot coil is produced from molten steel directly. In the twin roll strip casting process, molten steel supplied by the nozzle cools and solidifies due to the heat extraction effect of the rolls and hot rolling of the solidified shell takes place simultaneously. The analysis of hot rolling has been carried out by using the existing results of solidification analysis for the twin roll strip casting process. The current slab method provides basic design data such as roll separation force, rolling torque, rolling power as well as end dam separation force which are required to design strip caster. The effect of friction on the basic process parameters are investigated also. It is shown that the use of appropriate friction coefficient is important and that the characteristics of hot rolling in the twin-roll strip casting process is quite different from the conventional hot rolling processes.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.772-776
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• 1997

For a robot to perfom more versatile tasks, it is invitable for the robot's end-effector to come into contact with its environment. In thos case, to achieve better performance, it is necessary to properly control the contact force between the robot and the environment. In thos work, hybrid control theory is studied and is verified through experiment using a 3 DOF robot. In the experiment, two position/force controllers are used. Fist, proportional-integral-derivative controller is used as the controller for both position and force. Second, computed-torque method is used as the position controller, and proportional-integral-derivative controller is used as the force controller. For a proper modeling used in computed-torque method, the friction torque is measured by experiment, and compensation method is studied. The hybrid control method used in this experiment effectively control the contact force between the end-effector and the environment for various types of jobs.

• 반도체디스플레이기술학회지
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• 제3권1호
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• pp.15-20
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• 2004

Through shallow trench isolation (STI) chemical mechanical polishing (CMP) tests, we investigated the dependence of pad surface temperature on the abrasive and additive concentrations in ceria slurry under varying pressure using blanket film wafers. The pad surface temperature after CMP increased with the abrasive concentration and decreased with the additive concentration in slurries for the constant down pressure. A possible mechanism is that the additive adsorbed on the film surfaces during polishing decreases the friction coefficient, hence the pad surface temperature gets lower with increasing the additive concentration. This difference in temperature was more remarkable for the higher concentration of abrasives. In addition, in-situ measurement of spindle motor was carried out during oxide and nitride polishing. The averaged motor current for oxide film was higher than that for nitride film, meaning the higher friction coefficient.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.382-389
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• 2002

Recently, auger-drilled piling has been widely used in urban area to reduce the air pollution and noise. But this construction method that its basic theory was introduced from Japan may be changed depending on the each piling company and construction field condition. Therefore, the design code and management method for auger-drilled piling is not defined yet. Especially, the lack of research on the bearing capacity of auger-drilled piling leads to the absence of rational bearing capacity prediction equation. This paper presents the optimum design code and economical construction method of the auger-drilled piling by proposing the new bearing capacity prediction equation based on the site specific soil types and construction conditions. In this paper, existing bearing capacity prediction equations and current pile load tests were compared. And the end bearing capacity and skin friction characteristics were also analyzed by comparing the results of CAPWAP. From the results of analysis, a reliable bearing capacity prediction equation considered soil types is proposed.

• 한국지반공학회논문집
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• 제26권5호
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• pp.5-13
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• 2010

국내 풍화대 지반에 적용가능한 설계도표를 작성하기 위하여 2개소 현장에서 총 6개의 양방향고유양말뚝재하시험 및 하중전이시험을 수행하였으며, 또한 각각 위치에서는 한국형타격콘관입시험 (DCPT)을 수행하였다. 말뚝재하시혐의 결과로부터 심도별 최대단위선단지지력올 분석하였으며 DCPT 결과를 이용하여 이들의 상관성을 분석하였다. 토사(사질토, 점토)지반에서는 최대단위주변마찰력과 DCPT의 상관성이 매우 낮게 나타났으나 풍화대지반에서는 최대단위주변마찰력 / 최대단위선단지지력과 DCPT의 관계에서는 상관계수가 0.70이상으로 높게 나타났다.

• 한국지반신소재학회논문집
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• 제18권3호
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• pp.69-77
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• 2019

본 논문에서는 테이퍼 마찰말뚝의 자유진동을 평가할 수 있는 해석모델을 제안하였다. 불균질 지반에 설치된 정적 수직하중을 받는 테이퍼 마찰말뚝의 자유진동을 지배하는 미분방정식을 유도하였다. 이 지배방정식을 Runge-Kutta 법을 이용하여 직접 수치적분하였고, 미분방정식의 고유치인 고유진동수는 Regula-Falsi 법을 이용하여 산정하였다. 원통형 말뚝의 고유진동수 계산값은 기존 문헌값과 잘 일치하였다. 수치예를 통해 말뚝의 변단면, 주면마찰력, 단부조건, 수직압축하중 및 지반의 불균질성이 고유진동수와 모드형상에 미치는 영향을 분석하였다.

• 한국지반공학회논문집
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• 제33권11호
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• pp.59-72
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• 2017

본 연구에서는 사질토 뒷채움재의 캔틸레버 옹벽에서 뒷굽 끝단 연직면에 작용하는 주동토압을 산정하는 방법을 제안하였다. 캔틸레버 옹벽에서 뒷굽길이에 따른 전단 영역의 변화는 벽체의 벽마찰력, 뒷채움 경사에 따라 뒷굽 끝단 연직면에 작용하는 주동토압에 영향을 준다. 뒷굽길이에 따라 변하는 파괴면각도를 가정하여 토압을 산정하는 한계평형법은 적용하기에 매우 복잡하므로 본 연구에서는 한계해석법을 사용하여 토압을 구하였다. 한계해석법으로 뒷굽길이에 따라 실제 파괴면각도가 고려된 토압을 정확히 산정하고, 이로부터 뒷굽 끝단 연직면에 작용하는 수평토압과 연직토압을 분석하였다. 본 연구결과에 의하면, 뒷굽길이가 짧아짐에 따라 내측 파괴면 경사각은 이론식보다 증가한 반면에 외측 파괴면 경사각은 영향을 받지 않았다. 뒷굽 끝단의 연직면에 작용하는 배면마찰각은 지표면 경사각과 벽면마찰각 사이의 값을 나타내었으며, 주동토압 또한 감소하였다. 최종적으로 상대적인 뒷굽길이와 뒷굽 끝단의 연직면에 작용하는 마찰각(연직토압/수평토압의 비)의 상관관계를 사용함으로써 Coulomb 토압을 간편하게 산정할 수 있도록 하였다.