• Journal of Welding and Joining
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• 제17권5호
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• pp.83-88
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• 1999

In this paper resistance projection weldability of Zn coated steels with post treatment has been discussed. Projection welding was performed by a condenser discharge type power source which was equipped with welding parameter monitoring system. Mechanical test results indicated that the effect of post coatings on the projection front changed showing very small very small spattering at the weld strength was negligible. However, contamination rate of the block electrode varied depending on the post treatment coatings. Test results also showed that projection height before welding should be kept to be 80-100% of the specimen thickness as far as the surface quality was taken into consideration. Based on the high speed photography, discharge condition at the beginning stage of the welding process. It was considered that the spattering reduced the weld strength slightly at the optimum heat input range.

• 한국해양공학회지
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• 제13권2호통권32호
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• pp.66-73
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• 1999

This paper presents the experimental examinations and statistical quantitative analysis of the correlation between the cumulative counts of acoustic emission(AE) during plastic deformation periods of the welding and the tensile strength and other properties of the tube-to-tube welded joints of O.D. 30mm (I.D 18mm) nozzle steel. This is a new approach which attempts finally to develop real-time quality monitoring system for friction welding. And this study results in practical possiblility of real-time quality control more than 100% joint efficiency showing good weld no micro structural defects.

• 한국해양공학회지
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• 제13권1호통권31호
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• pp.88-93
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• 1999

This paper presents the experimental examinations and statistical quantitative analysis of the correlation between the cumulative counts of acoustic emission(AE) during plastic deformation periods of the welding and the tensile strength and other properties of the bar-to-bar welded joints of O.D. 16mm shaft(SM40C) as well as the various welding variables. And this is a new approach which attempts finally to develop real-time quality monitoring system for friction welding. The results lead to a practical possibility of real-time quality control more than 100% joint efficiency showing good weld with no micro structural defects.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1999년도 추계종합학술대회
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• pp.494-497
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• 1999

Neural networks are shown to be effective in being able to distinguish incomplete penetration-like weld defects by directly analyzing the plasma which is generated on each impingement of the laser on the materials. The performance is similar to that of existing methods based on extracted feature parameters. In each case around 93% of the defects in a database derived from 100 artificially produced defects of known types can be placed into one of two classes: incomplete penetration and bubbling. Especially we present simulator for weld defects classification and data analysis. The present method based on classification using plasma is faster, and the speed is sufficient to allow on-line classification during data collection.

• Journal of Welding and Joining
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• 제17권2호
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• pp.97-103
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• 1999

The dynamic resistance monitoring in primary circuit is one of the important issues. Because in-process and real time quality assurance of resistance spot weld is needed to increase the product reliability. In this study, new dynamic resistance detecting method is proposed as a practical manner of weld quality assurance using instantaneous current and voltage measured at the primary circuit. and also, various patterns of primary dynamic resistance curve are characterized with the macro photograph and the weldability lobe curve. It is found that the primary dynamic resistance patterns are basically similar to those of the secondary, but there is evident advantage such as no extra devices are needed to obtain the quality information and eventually real time feedback control will be possible.

• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.193-196
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• 2003

We have developed a laser welding monitoring system to monitor laser welding process conditions such as sample feed rate, laser focal position, and laser power. A 2 ㎾ Nd:YAG CW laser beam has been applied to the welding of a stainless steel plate (SUS306) to investigate the welding monitoring. Theradiation signal from the weld pool was guided back through the focusing optics and the laser delivery fiber, and measured by a photo detector. By changing the focus of the laser beam along the z-direction, the penetration depth of the welding material has been measured. That shows the penetration depth depends on the frequency fluctuations of the plume signals which can be used in welding quality control.

• 한국정밀공학회지
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• 제22권4호
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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.

• 한국해양공학회지
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• 제19권4호
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• pp.21-27
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• 2005

Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric discontinuities, as well as material discontinuities due to weld joints. The fatigue strength at these hot spots is very important for the structural performance. In the past, various Non Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, an important limitation of most of the existing NDE methods is that they are off line; the normal operation of the structure has to be interrupted, and the device often has to be disassembled. This study explores the development of a structural health monitoring system, with a special interest in applying the technique to welded structural members in ship and offshore structures. In particular, the impedance based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated.

• 한국산학기술학회논문지
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• 제10권3호
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• pp.515-520
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• 2009

본 논문에서는 알루미늄 레이저 용접에서 발생하는 플라즈마의 빛을 계측하여 용접공정을 모니터링할 수 있는 시스템을 개발하였다. 분광분석을 통해 용접 시 플라즈마의 파장대를 계측하고 이를 근거로 하여 모니터링 시스템에 적합한 포토다이오드를 선정하였다. 이를 다양한 용접 조건에 대하여 적용하였고, 센서 신호의 특성은 플라즈마의 강도와 안정성에 밀접하게 연관되어 있음을 신호의 평균값과 FFT분석을 통하여 알 수 있었다. 이러한 신호 변동의 원인은 플라즈마와 키홀의 거동과 용접 비드의 형상과도 밀접한 관계가 있음을 분석하였다.

• 한국정보통신학회논문지
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• 제9권6호
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• pp.1379-1386
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• 2005

현재 산업현장에서 활용하는 용접용 로봇은 대부분 오프라인(off-line)으로 작업을 수행하고 있어 생산성과 용접 품질 향상에 그 기능을 충분하게 발휘하지 못하는 실정이다. 현재에는 용접 품질 향상을 위하여 용접 매카니즘이 많이 연구되어 많은 수학적인 해석과 물리적인 해석방법을 도입하여 비선형적인 용접 메카니즘을 연구하고 있다. 이러한 여러 가지 비선형적인 문제와 해석상의 어려움에도 불구하고 용접의 결함을 보완하기 위해 보다 정확한 용접데이터를 생성하기 위하여 고감도의 센서를 도입하여 신호처리 하고 있으며, 이를 이용하여 용접시스템에 포함시키는 피드백제어시스템(feed-back control system)을 구성하여 용접선 추적 및 용접 비드(bead) 형상제어에 응용하고 있다. 또한, 최근에는 인공지능제어기술이 발달되어 인간의 학습능력과 의사결정능력을 대신하는 신경회로망(neural network)과 퍼지이론(fuzzy logic)을 도입하여 용접기술을 개발하고 발전시키고 있다. 본 연구에서는 신경회로망이론을 이용하여 실시간으로 용접시스템을 모니터링하고 퍼지제어기에 의하여 용접결함을 보정하는 지능시스템을 개발방법을 제시하고자 한다.