• Journal of Welding and Joining
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• 제30권1호
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• pp.59-63
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• 2012

The spacer grid is one of the main structural components in a fuel assembly. It supports fuel rods, guides cooling water and maintains geometry from external impact load and cyclic stress by the vibration of nuclear fuel rod, it is necessary to have sufficient strength against dynamic external load and fatigue strength. In this study, the mechanical properties and fatigue characteristics of laser beam welded zircaloy thin sheet are examined. The material used in this study is a zirconium alloy with 0.66 mm of thickness. The fatigue strength under cyclic load was evaluated at stress ratio R=0.1. S-N curves are presented with statistical testing method recommend by JSME- S002 and compared with S-N curves at R.T. and $315^{\circ}C$. As a result of the experimental approach, the design guide of fatigue strength is proposed and the results obtained from this study are expected to be useful data for spacer gird design.

• Journal of Welding and Joining
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• 제25권2호
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• pp.49-54
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• 2007

Since the wall thickness can be up to 6" or greater, welds must be made in many layers, each layer containing several passes. However, the welding time for the conventional welding processes such as SAW(Submerged Arc Welding) and FCAW(Flux Cored Arc Welding) can be required many hours. The aim of this paper is to develop a high speed welding system with multi-torch and laser vision sensor for increasing the production speed on the line and to remove the need for the operator so that the system can run automatically for the complete multi-torch multi-layer weld. It was shown that the developed laser vision sensor and analysis of arc blow for multi-torch were effective for multi-pass seam tracking and stable arc. A new automated multi-torch welding systems for thick wall applications has been proved in several production lines.

• Journal of Welding and Joining
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• 제25권1호
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• pp.49-56
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• 2007

Prediction and control of the thermal distortion is particularly important for the design and manufacture of welded thin plate panel. In this study, experiments and computations are performed to analyze effect of a hole configuration and a specimen size on distortion. In addition, this study aims to develop a thermal elasto-plastic simulation using finite element method to predict distortion, with particular emphasis on buckling deformation generated in plates welded around hole. From the experiments, the severe distortion appeared in the weldments by the laser welding process, in which the specimen size plays an important role on the distortion but the hole configuration showed little effect. And the results of numerical analysis were corresponded well with the experiment ones. Thus, a thermal elasto-plastic analysis model for predicting the weld distortion of thin plate panel was successfully developed through this study.

• Journal of Advanced Marine Engineering and Technology
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• 제32권2호
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• pp.315-322
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• 2008

Titanium and its alloys have excellent corrosion resistance, high strength to weight ratios and creep properties in high temperature, which make them using many various fields of application. Especially, pure titanium, which has outstanding resistance for the stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion, brings out to the best material for the heat exchanger, ballast tank, desalination facilities, and so on. Responding to these needs, welding processes for titanium are also being used GTAW, GMAW, PAW, EBW, LBW, resistance welding and diffusion bonding, etc. However, titanium is very active and highly susceptible to embrittlement by oxygen, nitrogen, hydrogen and carbon at high temperature, so it needs to shield the weld metal from the air and these gases during welding by non-active gas. In this study, it was possible to get sound beads without humping and spatter with a decrease of peak power according to increase of pulse width, change of welding speed and overlap rate for heat input control, and shield conditions at pulsed laser welding of titanium plates for Lap welding.

• 한국공작기계학회논문집
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• 제15권3호
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• pp.120-126
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• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range$({\Delta}K)$ region and faster in high ${\Delta}K$ region than that of the base metal specimens.

• 한국정밀공학회지
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• 제16권4호통권97호
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• pp.37-45
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• 1999

Many automated welding equipment are used in the industry. However, there are some problems to get quality welds because of the geometric error, thermal distortion, and incorrect joint fit-up. These factors can make the gap between base plates in case of a thick plate welding. The welding product with the quality welds can not be obtained without consideration of the gap. In this paper, the robot path and welding conditions are modified to get the quality weld by detecting the position and size of the gap. In this work, a low-priced laser range sensor is used. The 3-dimensional information is obtained using the motion of a robot, which holds a laser range sensor. The position and size of the gap is calculated using signal processing of the measured 3-dimensional information of joint profile geometry. The data measured by a laser range sensor is segmented by an iterative end point method. The segmented data is optimized by the least square method. The existence of gap is detected by comparing the data with the segmented shape of template. The effects of robot measuring speed and gap size are also tested. The recognizability fo the gap is verified as good by comparing the real joint profile and the calculated joint profile using the signal processing.

• Journal of Welding and Joining
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• 제34권6호
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• pp.69-74
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• 2016

Because the pure titanium has superior corrosion resistance and formability compared with different material, it is widely used as material of welded heat exchanger. When the welding of heat exchanger is carried out, certain area in which welding start and end are overlapped occurs. The humping of back bead is formed in the overlap area due to partial penetration. Thus in this study, the experiments were carried out by changing the length and wave shape of overlap area, and then the weldabiliay was evaluated through the observation of microstructure, the measurement of hardness and tensile-shear strength test in the overlap area. When overlap length was 9.8mm, humping bead was suppressed. The microstructure of overlap area coarsened and its hardness increased due to remelting. As a result of tensile-shear strength test in the overlap area according to applying the wave shape control, it was confirmed that the overlap area applied wave shape control had more excellent yield strength and ductility.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.143-150
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• 2003

Experimental research has been carried out to investigate the characteristics of the fatigue crack initiation and propagation behavior of Tailor Welded Blank(TB) sheet used for vehicle body. We used three types of specimens which were machined of the same base metal: one is 1.4mm thick, another is 1.6mm thick, and the third(TB specimen) is laser-welded of two specimens(1.4mm and 1.6mm thick ones). The results of tensile and hardness test indicate that the yield strength of the TB specimen is the highest, and the hardness around welding bead is higher than that of base metal. Fatigue strength and fatigue limit of the TB specimen are much superior to those of the base metal up to $10^6$ cycles. The fatigue crack propagation of the heat-affected zone of the TB specimen is slower than that of the base metal. Welding bead has the fastest crack Propagation in the low stress intensity factor range$(\DeltaK)$ region, but the slowest in the high $\DeltaK$ region. The fatigue propagation characteristic of the TB specimen is relatively stable in comparison with that of the base metal in the high ${\Delta}K$ region around over $28MPa\sqrt{m}$.

• 한국정보통신학회논문지
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• 제6권8호
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• pp.1374-1380
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• 2002

용접을 하는데 있어서 보다 균일한 용접상태를 유지하고, 용접품질의 향상 및 동일시간에 보다 많은 용접을 함으로써 생산성 향상을 위해 로봇의 이용이 점차로 증가하고 있다. 로봇용접의 과정 중 실제 용접을 실시하기 위해 로봇을 움직이기 이전에 용접할 부위의 검출이 선행되어야 하고, 그 검출방법에 있어서 크게 접촉식과 비접촉식의 센서가 활용이 되고 있다. 본 논문에서는 비접촉식 중 비전센서인 레이저 다이오드와 CCD 카메라를 이용하여 CCD 카메라를 거친 영상을 처리하여 용접선을 추적하고 용접을 하도록 하고 있다. 레이저 다이오드를 용접모재와 일정 각도를 가지도록 조사하게 되면 모재표면의 형상에 따라 반사되는 굴곡면이 달라지게 되는데 이 형상이 CCD 카메라를 통해 입력되고, 이 입력된 화상을 이미지 보드와 프로그램을 통하여 분석을 하고, 얻어진 용접선의 화상의 좌표 값을 토대로 로봇을 이동시킴으로써 용접을 하도록 하고 있다. 용접은 실시간으로 이루어짐으로써 생산성 향상에 크게 기여할 수 있다. 또한 모재에 따라 굴곡이 다른 1차원 평면의 용접인 경우는 약간의 프로그램 수정으로 대부분 추적 가능하다는 것을 확인할 수 있었다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.460-464
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• 2001

최근, 아크용접을 하는데 있어서 보다 균일한 용접상태와 용접품질의 향상 및 동일시간에 보다 많은 용접을 함으로써 생산성 향상을 위해 로봇의 이용이 점차로 증가하고 있다. 로봇용접의 과정 중 실제 용접을 실시하기 위해 로봇을 움직이기 이전에 용접할 부위의 검출이 선행되어야 하고, 그 검출방법에 있어서 크게 접촉식과 비접촉식으로 대별된다. 본 논문에서는 비접촉식 중 영상처리센서인 레이저 다이오드와 CCD 카메라를 이용하여 CCD 카메라를 거친 영상을 처리하여 용접선을 추적하고 용접을 하도록 하고 있다. 레이저 다이오드를 용접모재와 어떤 각도를 가지도록 조사하게 되면 모재표면의 형상에 따라 반사되는 굴곡면이 달라지게 되는데 이 형상이 CCD 카메라를 통해 입력되고, 이 입력된 화상을 이미지 보드와 프로그램을 통하여 분석을 하고, 얻어진 용접선의 화상의 좌표 값을 토대로 로봇을 이동시킴으로써 용접을 하도록 하고 있다. 용접은 실시간으로 이루어짐으로써 생산성 향상에 크게 기여할 수 있다. 또한 모재에 따라 굴곡이 다른 1차원 평면의 용접인 경우는 약간의 프로그램 수정으로 대부분 추적 가능하다.