• Journal of Welding and Joining
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• v.15 no.6
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• pp.13-23
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• 1997

폭발용접은 화약의 폭발에 의한 충격 에너지를 이용하여 금속을 접합시키는 방법으로서 화약의 폭발에 의해 생기는 순간적인 높은 에너지를 이용하는 접합법이다. 1944년에 처음으로 폭발용접의 기술적, 상업적인 이점으로 인해 수요가 증가하고 있는 실정이다. 적용 예는 거대한 판재의 cladding을 포함하여 cladding nozzle, tube 와 tubeplate의 접합, pipe와 pipe의 접합등에 사용되고 있다. 종래의 용접법으로는 용접이 곤란하거나 불가능한 것으로 생각되었던 이종금속에 대해서는 적용이 가능하 고, 용접에 의한 열영향을 받지 않으며 용접 속도가 대단히 빠르다는 잇점이 있다. 또한 용접의 차이가 커서 접합이 곤란한 금속을 폭발용접하면 이음부는 충분한 강도를 가지면서 용이하게 접합할 수 있는 것이 큰 특징이다. 대부분의 금속은 폭발용접이 가능하지만 폭발의 충격에 의해서 균열이 발생되기 쉽고 주철과 같이 취약한 금속 및 Mg을 함유한 알루미늄 합금(순 알루미늄과는 접합 가능함)등은 이 용접법을 사용하기 는 곤란하다. 시공상의 특징으로는 특별한 기계 장치가 필요하지 않고 모재가 판재 혹은 파이프상이면 모재 두께에 제한 받지 않고, 어떠한 형태와도 가능하기 때문에 다품종, 소량생산이 가능하다. 한편 접합시에 화약을 사용하기 때문에 취급에 있어서 주의를 요하고 큰 폭발음 때문에 용접장소의 제한을 받는다는 것이다.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.98-103
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• 2008

This paper is to discuss distribution of welding residual stresses of a ferritic low alloy steel nozzle with dissimilar metal weld using Alloy 82/182. Two dimensional (2D) thermo-mechanical finite element analyses are carried out to simulate multi-pass welding process on the basis of the detailed and fabrication data. On performing the welding analysis generally, the characteristics on the heat input and heat transfer of weld are affected on the weld residual stress analyses. Thermal analyses in the welding heat cycle process is very important process in weld residual stress analyses. Therefore, heat is rapidly input to the weld pass material, using internal volumetric heat generation, at a rate which raises the peak weld metal temperature to $2200^{\circ}C$ and the base metal adjacent to the weld to about $1400^{\circ}C$. These are approximately the temperature that the weld metal and surrounding base materials reach during welding. Also, According to the various ways of appling the weld heat source, the predicted residual stress results are compared with measured axial, hoop and radial through-wall profiles in the heat affected zone of test component. Also, those results are compared with those of full 3-dimensional simulation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.114-118
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• 2007

Design and fabrication of a 30-tonf-class full-scale regenerative cooling combustion chamber of a liquid rocket engine for a ground hot firing test are described. It has chamber pressure of 60 bar and nozzle expansion ration of 12 and manufactured to have a single welded structure of· the mixing head and the chamber. The material of the mixing head is STS316L which has excellent mechanical property in cryogenic condition. The chamber comprise of the cylinder, nozzle throat, and 1st/2nd nozzle parts. The material of the inner jacket is copper alloy/STS329J1/STS316L and that of the outer jacket is STS329J1. The components of· the combustor were manufactured by mechanical processing including lathing, milling, MCT, rolling and pressing. The machined components were integrated to a single body by means of general welding, electron beam welding(EBW), and brazing.

• Transactions of Materials Processing
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• v.17 no.7
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• pp.523-527
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• 2008

In this study, mechanical properties of Alloy 718 welded after forgings for jet propulsion component was investigated. Hot-forged and machined work-pieces($230mm\times70mm\times15mm$) which have different grain sizes are welded by electron beam welding technique. After welding, the components were solution heat-treated and aged. Samples were sectioned to analyze the microstructural evolution and formation of micro-crack. It was found that HAZ grain boundary liquation crack generally initiates in the coarse grains rather than the fine grains. Needle-like phases with high Nb contents were found at the outer part near the base metal. Vickers hardness and tensile tests were carried out at room temperature and at $649^{\circ}C$. The tensile properties of electron beam welding specimens exhibited around 100MPa and 10% decrease in strength and elongation, respectively.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.1
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• pp.53-60
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• 2015

This study was investigated to develop process technology of laser cladding with austenite stainless steel for Weld Inlay repair of dissimilar metal weld in reactor vessel in/outlet nozzles. Weld Inlay experiments were performed by laser cladding repair system consisting of common manipulator, laser apparatus and welding process scheduler, etc. Single pass welding experiments were conducted in order to obtain the optimum welding process parameters for filler wires of ER309L and Alloy 52M before multi-layer laser cladding. Based on the above obtained results, multi-layer laser cladding experiments were carried out, and welding qualities for weld specimens were estimated by PT, OM, SEM and EDS analysis. Consequently, it was revealed that multi-layer laser cladding on austenite stainless steel using filler wires of ER309L and Alloy 52M could be possible to meet ASME Code standard without any weld defect.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.2
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• pp.294-301
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• 2012

Shipbuilding industry has used a lot of $CO_2$ gas as a shielding gas for arc welding and thus, development of welding equipment which can reduce the amount of $CO_2$ gas is requested widely. Therefore, this study is focused on the examination of optimum welding torch distance of Tandem welding system as a fundamental study for the optimum shape design of torch nozzle. $CO_2$ shielding gas distribution and welding bead shape formation by the torch distance are examined. Results show that according to the torch distance variation, most effective shielding gas layer can be formed and quantitative determination of the optimum torch distance can result in the reduction of $CO_2$ shielding gas consumption.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.7
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• pp.664-672
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• 2009

Nozzle in nuclear power plant is connected to pipe using safe end. Dissimilar metal weld between nozzle and safe end is followed by similar metal weld between safe end and pipe. And thus residual stress in dissimilar metal weld can be affected by similar metal weld. Similar metal weld impose bending stress on dissimilar metal weld, which is according to the length of safe end. In this study, simple nozzle model which covers various radius to thickness ratios was proposed to quantify residual stress in dissimilar metal weld based on finite element analyses. As a result, short length of safe end was proved to be more effective to mitigate residual stress in dissimilar metal weld and critical effective length of safe end is provided according to the radius to thickness ratio.

• Journal of Welding and Joining
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• v.6 no.3
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• pp.37-42
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• 1988

The Hole Drilling Method(HDM) is widely used to measure residual stresses in the welded structures. The purpose of this study is to evaluate the accuracy fo measuring residual stresses when drilling the hole by Air-abrasive Jet machine(AJM). Simulated residual stresses wre introduced by applying known stresses to steel bars. These known streses were then compared with measured stresses relaxed from hole drilling. the obtained results are summarized as follows; 1) It was possible to obtain well defined holes with the nozzle designed for this study. 2) If the hole shape is not cylindrical, critical may occur. 3) In the uniaxial strain field, the measurement error of the maximum principal stress was within .+-.10 percent. The orientation angle of the maximum principal stress was within 8.deg. from the given directioin. 4) meausrements were made varying hole depths. Little or no change of stresses occurs since holse were drilled more than the depth of the 0.6 times diameter. 5) The air-abrasive jet machining for drilling holse does not cause appreciable apparent stresses which si critical to measure residual stresses.

• Journal of Welding and Joining
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• v.17 no.6
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• pp.46-52
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• 1999

The auxiliary gas-shielded MAG (AMAG) process, which was devised to provide an argon-rich shielding environment using small amount of argon gas, was investigated experimentally to figure out its effects on metal transfer and weld quality. Proper conditions for the AMAG process including the argon gas ratio, position and direction of the auxiliary nozzle were determined experimentally. Performance of the AMAG process was compared with that of the double gas-shielded MAG(DMAG) and MAG processes by monitoring the bead profile, current and voltage waveforms. The AMAG process was found to provide better bead profile, more stable arc and wider operating range of spray transfer mode compared with the DMAG process. In general, performance of the AMAG process using the argon ratio of 30% was comparable to that of the MAG process using 80% argon and 20% CO₂ gas.

• Journal of Welding and Joining
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• v.12 no.2
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• pp.1-10
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• 1994

노즐에서 분사되는 제트의 거동에 대해 전반적으로 고찰해보고, 실제 후판의 레이저 절단성 실험 을 통해 노즐의 영향 및 혼합가스의 절단면 질 향상효과 등을 살펴보았다. 간략히 요약하면 다음 과 같다. 아음속제트는 노즐압력을 증가함에 따라 절단압력도 증가하지만 노즐과 재료사이의 거 리를 가능한 작게 유지하여야 하는 제약이 있다. 따라서 사용중에 손상이 가기 쉽다. 이를 해결하 고자 초음속제트의 사용이 연구되고 있지만 shock의 형성으로 인해 노즐압과 절단압은 매우 비선 형적인 관계를 갖는다. 따라서 (i)고압에서도 MSD가 형성되지 않고 주기적인 압력 재상승이 나 타나도록 하거나, (ii)Laval노즐을 이용해 shock구조가 형성되지 않고 큰 절단거리를 얻도록 하는 방법이 제시되고 있다. 초음속노즐의 후판 절단 적용 가능성을 분석해 본 결과 유동 박리 현상으 로 인해 후판보다는 박판의 향상을 위해서는 적절한 조성의 혼합가스를 사용하는 것이 아주 효과 적이었으며, 보조 가수 제트를 채용해 slag제거를 효율적으로 수행 할 수 있음을 확인하였다.