• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.204-207
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• 2001

The bending process for the circular curved tube and rectangular curved tube with fins can be developed by the hot metal extrusion machine with the multiple punches moving in the different velocity. The bending phenomenon can be controlled by the two variables. The one of them is the difference of velocity at the die exit section by the different velocity of billets through the multi-hole container. The other is the one by the different hole diameter. The results of the experiment show that the circular curved tube with fins and rectangular curved tube with pins can be formed by the extrusion process and that the curveture of the product can be controlled by the velocity of punch and diameter of container hole and that the defects such as the distortion of section and the thickness change of the wall of tube the folding and wrinkling of thin tube and fins did not happen after the bending processing by the extrusion bending machine.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.98-100
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• 2002

We developed the Centrifugal Forming Process(CFP) for HTS tube fabrication. The self-designed equipment for CFP is devided into 3 main parts depending on its role and functions. the melting part by heating of high inductive frequency, centrifugal forming part for the tube and efficient microstructure control of Bi2212 phase and molding part for tube detachment after heat treatment. In this paper we will introduce self designed Centrifugal Forming Process for HTS tube fabrication and discuss about the results related mold materials in terms of high Tc superconductor.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1508-1516
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• 2003

In numerical analysis for hydroforming process, the stress calculation is effected by flow stress which is general obtained by stress-strain relationship from uni-axial tension test, so the result of the analysis, especially in tube hydroforming, has limitation of accuracy, tubes are made in roll-forming process and become work-hardened. Then roll forming process causes material properties between rolling direction and circumstantial direction of the tube to be different. So it is difficult to predict material behavior in the process condition of bi-axial stress state. In this study, the flow stress of the tube is determined by inverse engineering approach and bulge test that is widely used for formability test in the condition of bi-axial stress. And Hill's quadratic yield function and flow rule are used to consider the anisotropy of the tube in the roll forming process.

• 소성∙가공
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• 제18권1호
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• pp.67-72
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• 2009

This paper covers finite element simulations to evaluate tube bending process of auto chassis component i.e. trailing-arm product. The rear of the auto chassis structure is primarily composed of CTBA and trailing-arm. When a car rolls into a corner, the trailing arm reacts to roll in the same degree as the car body. During the bending process of trailing arm the tube undergoes significant deformation. Thus forming defects such as excessive thinning and flattening of the tube will be formed in the outside of the tube. In this paper, we analyzed the effect of process parameters in rotary draw bending process and searched the optimized combination of process parameters using orthogonal arrays method to minimize the forming defects. In this process we analyzed several parameters which are displacement of pressure die, boosting force, initial position of mandrel bar, dimensions of mandrel in regarding to the thinning and flattening of the tube.

• 소성∙가공
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• 제31권3호
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• pp.143-150
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• 2022

The purpose of this study was to investigate an innovative hydroforming process for the cost-effective manufacturing of double layered tube with circumferentially corrugated patterns. Conventional double pipe heat exchanger has relatively poor heat transfer efficiency because of the limited contact area resulting from the concentrically arranged simple cylindrical structure. As a promising alternative to enhance heat transfer efficiency, double layered tube with corrugated internal pattern was considered in this study. To fabricate corrugated inner tube, innovative tube hydroforming system was developed. The customized loading paths were established using the simulated forming pressure and contracting stroke at various bar diameters. Experimentally obtained cross-sectional profiles were analyzed to evaluate the reliability and applicability of the hydroformed tube with various patterns. The results demonstrate that the proposed hydroforming process can be a feasible alternative for manufacturing high-performance double-tube heat exchangers.

• 한국추진공학회지
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• 제17권3호
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• pp.37-46
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• 2013

최근, micro shock tube는 Micro combustion, Micro propulsion, Particle delivery systems 등과 같은 다양한 공학응용분야에서 사용 되고 있다. Micro shock tube 에서 일어나는 유동 특성은 아주 작은 레이놀즈수 와 높은 누센수의 영향으로 인해 잘 알려진 기존의 macro shock tube 유동 특성과 상당한 차이가 나타난다. 또한 기존의 많은 shock tube의 순간적 과정으로 간주되는 격막파막 과정은 micro shock tube의 격막 근처의 유동장과 충격파 형성을 결정하는 중요한 요인이 될 것이다. 본 논문에서는 micro shock tube를 모사하기 위해 축 대칭, Maxwell's 슬립속도 조건과 온도 변화 경계 조건을 적용하여 수치 해석을 수행 하였다. 또한 유동장과 충격파 형성에 대한 유한 파막 과정의 영향을 자세히 조사 하였고, 결과로부터 충격파 강도는 micro shock tube를 통해 전파됨에 따라 급격히 감소하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1888-1891
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• 2003

In this paper, we proposed a new method to control the length of carbon nano tube in the single CNT probe. A single CNT probe was composed of a tungsten tip made by the electrochemical etching and carbon nano tube which was grown by CVD and prepared through the sonication. The two components were attached with the carbon tape. Since the length of CNT can not be controlled during the manufacturing, the post process is needed to shorten the CNT. In this paper, we proposed the method of electrochemical process. The process was done under the optical microscope and the results were checked by SEM. The diameter of the carbon nano tube used in this paper was about 130nm because the above process had to be done with the optical microscope. Using the method proposed in this paper, we can control the length of the nano tube tip.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 춘계학술대회 논문집
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• pp.25-28
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• 2002

This paper is concerned with the design of roller profiles in tube/pipe straightener with both methods of Computer Aided Design and Computer Aided Engineering. Design analysis is carried out from two point of view. The one is the research in the minimization of tube pitch which was very important factor in levelling process. In order to minimize tube pitch, profiles of the roller were calculated so that the contact region between roller and tube was maximized. The other is determination of an optimum amount of intermesh for the proper progress without a jam in levelling process. Generally the jamming trouble was casued by excessive amount of intermesh in levelling process. The optimum amount of intermesh was determined through the finite element analysis.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.309-317
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• 2012

Recent years have witnessed the use of micro shock tube in various engineering applications like micro combustion, micro propulsion, particle delivery systems etc. The flow characteristics occurring in the micro shock tube shows a considerable deviation from that of well established conventional macro shock tube due to very low Reynolds number and high Knudsen number effects. Also the diaphragm rupture process, which is considered to be instantaneous process in many of the conventional shock tubes, will be crucial for micro shock tubes in determining the near diaphragm flow field and shock formation. In the present study, an axi-symmetric CFD method has been applied to simulate the micro shock tube, with Maxwell's slip velocity and temperature jump boundary conditions. The effects of finite diaphragm rupture process on the flow field and the shock formation was investigated, in detail. The results show that the shock strength attenuates rapidly as it propagates through micro shock tubes.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1996년도 춘계학술대회논문집
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• pp.40-47
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• 1996

An upper bound solution of tube drawing process using a fixed tapered plug has been obtained , which reduces to an solution for tube sinking by setting friction factor between tube and plug at zero. Effects of various process paraments have been discussed based on the solution.