• Journal of the Korean Society for Precision Engineering
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• v.22 no.4
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• pp.60-67
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• 2005

Compared with conventional welding, laser spot welding offers a unique combination of high speed, precision and low heat distortion. This combination of advantages is attractive for manufacturing industries including automotive and electronics companies. In this paper, a real time monitoring scheme fur a pulsed Nd:YAG laser spot welding was suggested. Acoustic emission (AE) signals were collected during welding and analyzed for given process conditions such as laser power and pulse duration. A back propagation artificial neural network, with AE frequency content inputs, was used to predict the weldability of stainless steel sheets.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.4
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• pp.384-394
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• 2002

In this paper, a new control strategy is proposed to improve the quality of the welding products. The conventional nonlinear power control system of spot welders is linearized using nonlinear feedback linearization technique based on differential geometry theory. An evolution strategy(ES) geometry is used to find optimal gain of PI controllers. It tries to find out the optimal control parameters by imitating the natural evolution. Some Simulation and experimental results show that the proposed variable power control system using ES algorithm has better dynamic performances than the conventional one.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.125-127
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• 2006

A spacer grid assembly, which is an interconnected array of slotted grid straps and is welded at the intersections to form an egg crate structure, is one of the main structural components of the nuclear fuel assembly for pressurized water reactors(PWRs). The spacer grid assembly is structurally required to have enough buckling strength under various kinds of lateral loads acting on the nuclear fuel assembly so as to keep the nuclear fuel assembly straight. To meet this requirement, it is necessary to weld the welding parts carefully and precisely. In this study, weld qualities such as, weld bead size, penetration, spatter, etc. manufactured by various welders were compared and analyzed. Comparison results show that the weld qualities could be improved by selecting the optimal welding condition and also improving the welding technique.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.42-44
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• 2006

A spacer grid assembly, which is an interconnected array of slotted grid straps and is welded at the intersections to form an egg crate structure, is one of the main structural components of the nuclear fuel assembly for pressurized water reactors(PWRs). The spacer grid assembly is structurally required to have enough buckling strength under various kinds of lateral loads acting on the nuclear fuel assembly so as to keep the nuclear fuel assembly straight. To meet this requirement, it is necessary to weld the welding parts carefully and precisely. In this study, a series of welding tests were carried out to find an optimum welding condition. After examining and analyzing the specimens welded from the welding conditions, a recommendable laser welding condition was selected for the KAERI designed Zircaloy spacer grid assembly.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.109-111
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• 2005

Nuclear fuel assemblies for pressurized water reactors(PWR) are loaded in the reactor core throughout the residence time of three to five years. A spacer grid assembly, which is an interconnected array of slotted grid straps and is welded at the intersections to form an egg crate structure, is one of the main structural components of the nuclear fuel assembly. The spacer grid assembly is structurally required to have enough buckling strength under various kinds of lateral loads acting on the nuclear fuel assembly so as to keep the nuclear fuel assembly straight. To meet this requirement, it is necessary to weld the welding parts carefully and precisely. In this study, laser welding qualities of the spacer grid assembly welded by several welding companies, such as weld strength, weld penetration depth, and weld bead size, are examined and compared.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.301-306
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• 2001

In this paper, friction welding optimization for 1Cr0.5Mo to STS304 and AE applications for the weld quality evaluation were investigated The important results of this study are as follows : 1. The techiques for dissimilar friction welding optimization if the elevated temperature materials 1Cr0.5Mo and STS304 and its real-time weld quality evaluation by AE were developed, considering on both strength and toughness. 2. Quantitative relationship was identified among welding condition, weld quality and cumulative AE counts.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.75-81
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• 2012

Dissimilar material friction welding such as STD11 and SCM440, we are considering of such things as strength and tenacity of welding interface, which consist of friction welding rotation frequency, friction heating pressure, upset forging-pressure, friction heating time, and upset forging-pressure time. From the study, obtaining the interrelationship between welding condition and quality(toughness, tenacity), we can set the best range of welding condition. while performing acoustic emission examination for the nondestructive evaluation, we can deduce the interrelationship among total acoustic emission counts, friction welding variable, and quality during friction welding, which can solve the manufacturing difficulty and enhance the economic value.

• Journal of Welding and Joining
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• v.1 no.2
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• pp.69-75
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• 1983

Both in-process quality control and reliability of the weld is one of the major concerns is applying friction welding. No reliable nondestructive monitoring method is available at present to determine the weld quality particularly in process of production. So that, this paper presents an experimental examination and quantitative analysis for the effects of initial acoustic emission(AE) counts on the weld strength relating to the rotating speed as a new approach which attempts finally to develop an on-line quality monitoring system design for friction welds using AE techniques. As one of the important results, it was well confirmed that the initial AE counts occurring during plastic deformation period of welding were quantitatively correlated with reliability at 95% confidence level to the joint strength of welds, tube-to-tube (SM 20 C to STS 304) and then an AE technique using the initial AE counts can be reliably applied to in-process strength monitoring of the weld.

• Journal of Welding and Joining
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• v.17 no.2
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• pp.53-60
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• 1999

Conventionally, CCD camera and vision sensor using the projected pattern of light is generally used to inspect the weld bead defects. But with this method, a lot of time is needed for image preprocessing, stripe extraction and thinning, etc. In this study, laser vision sensor using the scanning beam of light is used to shorten the time required for image preprocessing. The software for deciding whether the weld bead is in proper shape or not in real time is developed. The criteria are based upon the classification of imperfections in metallic fusion welds(ISO 6520) and limits for imperfections(ISO 5817).

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.66-66
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• 2010

국내 화력발전의 $CO_2$배출량을 크게 줄이고, 친환경, 그린 화력발전시스템을 위한 가장 효과적인 수단은 발전효율을 획기적으로 증대시키는 것이기 때문에 이를 목표로 한 기술개발은 경제적으로나 산업적으로 파급효과가 매우 크다. 발전효율 증대를 위한 핵심기술은 증기터빈의 성능향상이다. 현재 일본, 미국, EU 등 각국이 가장 관심을 가지고 기술개발에 심혈을 쏟고 있는 초내열, 내식 합금소재는 $700^{\circ}C$이상에서 기계적 성능을 보장할 수 있는 Ni기 합금개발이고, 현재까지 상당한 기술수준에 이르고 있는 것으로 파악되고 있다. 국내의 경우는 관련기술개발을 위해 연구가 진행되고 있으나, 기술적으로 아직 미흡한 수준이다. Ni기 초내열, 내식합금을 개발해서 그것을 화력발전용 증기터빈 부품, 특히 초내열합금 용접형 터빈로터 소재로 이용하기 위해서는 체계적이고 실용적인 연구를 통하여 용접형로타의 내구성과 신뢰성이 보장되는 최적 수준의 접합기술 개발이 선행되어야 한다. 따라서 본 연구는 선행연구로 $700^{\circ}C$이상 초내열/내식 Ni기 합금소재의 용접기술 개발을 위한 후보 소재 Alloy 617의 동종재료 용접 기술 개발을 목표로 한다. 본 연구는 Alloy617 12.6t 맞대기 이음으로 U그루브 내로갭 TIG용접을 하였다. 1pass 1layer 방식으로 총 8pass 8layer로 용접하였다. 전류 및 용접속도는 동일하게 두고 실드가스를 Ar 또는 Ar-$H_2$ 가스로 변경하여 시험하였다. Ar가스 TIG용접은 비드표면에 산화스케일이 생기고, 비드면이 거칠며 전체적으로 산화되었다. 반면에 Ar-$H_2$가스 TIG용접은 비드표면에 산화스케일이 없으며 표면이 미려하고 산화되지 않았다. 실드가스에 수소가스 첨가시 환원성가스로 역할을 하게 되고 이에 따라 용융지 표면에 산화피막을 제거하여 용접비드를 청정하게 하는 효과를 가진다.