• Journal of Advanced Marine Engineering and Technology
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• v.28 no.1
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• pp.109-115
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• 2004

The spatter and porosity could be occurred during$CO_2$CW laser welding of Primer- coated steel for shipbuilding. This study has suggested an alternative idea by examining of weld-defect formation mechanism. The primer-coated plate induced the spatter humping bead and porosity and these are main part of the welding defect. attributed to the powerful vaporizing pressure of primer attached on the base metal The zinc of Primer has a boiling point that is the lower temperature than melting point of steel zinc vapor will build up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Therefore introducing a small gap clearance in the lap position. the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, we suggested the occurred and prevented mechanism of weld defects with searching the factor.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.6
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• pp.728-735
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• 2003

This paper shows the possibility of performing Lap joint using the friction stir welding with $2mm^t$ aluminum alloy plate and the determination of tool-dimensions for FSW in milling machine. This research also is reported on obtaining the tensile-shear strength, 91.3 (MPa) and the energy absorption, 26.3 (J) for Lap jointed specimen. The optimal tool-dimensions and method for Lap joint using FSW is as follows; each diameter of shoulder and pin is $9\phi(mm) and 3\phi(mm)$, the length of pin is 3.6(mm), Pressing the shoulder of tool into original base metal is not reasonable.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.88-91
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• 2001

New type of vehicles made from thin aluminum alloy are under rapid development and some product are already on the market, but when welding sheet metal joint of aluminum alloy, the main problem are burn-through by the high heat input. The purpose of this study, it is to prevent the burn-through and to shallow penetration that AC pulse welding has diminish the penetration and to lower the droplet temperature at Al sheet metal welding. In this study, we observed the bead appearance and whether it was appeared burn through or not , as the variation of the root gap in the lap and butt-joint welding process.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.135-138
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• 2009

Quality evaluation of laser welded MCFC separator panels with large active area was performed. Lap joint was applied to produce stable air-tight seam weld by employing Nd:YAG laser. Results showed that surface contamination played a key role to form weld defects at the joint interface. However, there was no evidence that weld width at the lap joint changed after the stack operation time of 2,890h. Test results also revealed that the reinforcement values which were measured on the weld line after long time operation, were stable.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.180-182
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• 2005

Development of FSW for use in lap joint production would expend the number of applications that could benefit from the technique. In the study, an extensive investigation was carried out on FSW lap joints, including interface morphology and mechanical properties. Welding variables included welding speed, rotation speed and, of particular importance, lap joint a methods. Examination of metallographic cross sections and failure locations showed a critical sheet interface present in all welds. Results indicates FSW lap joints may potentially replace other joining processes like resistance spot welding and riveting.

• Laser Solutions
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• v.5 no.3
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• pp.1-8
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• 2002

Finite element analysis and experiment were peformed to estimate the fatigue strength for the lap joint of laser weld. To consider quantitatively residual stress which effects on the fatigue strength of the lap joint of laser weld, after three dimensional modeling for the longitudinal and transverse direction, residual stress fields in the weldment were calculated using thermo-elastic-plastic finite element analysis, then the equivalent fatigue stress considering the residual stress was obtained. To ensure reliability of calculated fatigue strength, fatigue tests were performed. The calculated and experimental results showed a good agreement. The fatigue strength considering a residual stress was lower than that of without considering a residual stress in the lap joint of laser welding. The fatigue strength in the transverse direction was higher than that of longitudinal direction.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.226-228
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• 2005

Of typical welding techniques, to employ the heat for joining process is the most commonly used welding process. But there arise difficulties when this process is applied to light weight alloys such as Aluminium alloy. In this respect, Friction Stir Welding(FSW), a solid-state joining process, is the most effective welding technique with significant potential for various industrial applications. In this study, the characteristics of lapping FSW Al 5052 alloy are shown under a variety of welding parameters such as the rotation speed of FSW tool and welding velocity. Conclusively, the welding properties of lapping FSW Al 5052 were found to be dominated by the deformation of non-joining area near the welding nugget rather than other factors such as the thermal input.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1069-1075
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• 2012

Laser is high density heat source, so it can make high speed welding with minimum heat input possible. Especially the high power fiber laser is recently commercialized and has high beam quality and the smallest system size compared with conventional laser due to it's unique oscillating mechanism. Because of these advantages it's thought that the most suitable heat source for LNG cargo tank welding precess which has to be conducted inside of ships. In this study fiber laser was used for welding of stainless steel for LNG carrier to applicate laser welding technique for shipbuilding industry. 1.2mmt STS304L of austenite stainless steel which apply to cargo tank was used for fiber laser welding. Butt and lap welding was conducted changing laser power, welding speed, then penetration characteristic was analyzed and optimal parameters for each materials. Consequently, we found that same or better mechanical properties were obtained in weld compared to base metal.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2859-2865
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• 2011

The welded connection is known as an essential factor for establishing qualified construction and/or maintenance of wrapped steel pipe. In this study, welded connection conditions in the coated pipes with large diameter (over 700 mm) in Korea water distribution systems were estimated for suggesting technically and economically available welded connection method. For the study analysis, current steel pipe usage and accident cases were investigated. In addition, the characteristics of each welded connection method and automatic or manual connection techniques were also compared and estimated. As results, automatic welded connection method is superior than manual welded connection method in aspect of pure construction cost (average 9%) or pure welded connection cost (average 13.5%). When the poor welding-working situations in Korea are considered such as high tolerance of out-of-roundness in KS regulation, a number of lap joint welded connections, the real cost benefits of automatic welded connection should be much higher than those of manual welded connections.

• Journal of Welding and Joining
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• v.26 no.1
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• pp.69-75
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• 2008

Spot welding which use the main process for side block production of stainless steel railway vehicle is legged behind in laser welding about a quality and productivity. Although the laser welding has many potential advantages such as low heat input and aspect ratio of weld bead, its application to a new structural component still is required many engineering data including mechanical properties such as tensile, fatigue strength, etc on. Therefore, experimental analysis was carried out to understand the fatigue phenomena of different thickness stainless steel overlap joining panels by Nd:YAG laser welding. The fatigue life curves were obtained through fatigue tests with the various levels of applied load. The fatigue life is related with the parameters such as gap size and penetration depth through experiment. As the results, tensile strength and fatigue life were proportional in heat input level and gap was identified the major factor for fatigue life. Also we could know that deferent a-ferrite content at HAZ depend on welding heat input was important factor to determine a formation of initial crack and total fatigue life cycle.