• Journal of Welding and Joining
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• 제17권6호
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• pp.25-31
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• 1999

Stainless steel sheets are commonly used for vehicles such as the bus and the train. These are mainly fabricated by spot-welding. By the way, its fatigue strength is lower than base metal due to high stress concentration at the nugget. edge of the spot-welding. By the way, its fatigue strength is lower than base metal due to high stress concentration at the nugget edge of the spot-welding point. Especially, it is influenced by welding conditions as well as geometrical factors of spot welded joint. Therefore, it is not too much to say that structural rigidity and strength of spot-welded structures is decided by fatigue strength of spot welded lap joint. Thus, it is necessary to establish a reasonable and systematic long life design criterion for the spot-welded structure. In this study, numerical stress analysis was performed by using 3-dimensional finite element model on IB-type spot-welded lap joint of 304 stainless steel sheet under tension-shear load. Fatigue tests were also conducted on them having various thickness, joint angle, lapped length, and width of the plate. From the results, it was found that fatigue strength of IB-type spot-welded lap joints was influenced by its geometrical factors, however, could be systematically rearranged by maximum principal stress ({TEX}$σ_{1max}${/TEX}) at the nugget edge of the spot-welding point.

• Journal of Welding and Joining
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• 제17권6호
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• pp.32-37
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• 1999

Since stainless steel plates have good mechanical properties, weldability, appearance and resistance of corrosion, these are traditionally used for vehicles such as the bus and the train. And they are mainly fabricated by spot welding. But fatigue strength of their spot welded joint is considerably influenced by welding conditions as well as geometrical factors. Thus a reasonable and systematic criterion for long life design of spot welded body structure must be established. In this report, strain energy density was analyzed by using 3-dimensional finite element model about the IB-type spot welded lap joint under tension-shear load. Fatigue tests were conducted on them having various thickness, joint angle, lapped length and width. From their results, it was found that fatigue strength of the IB-type spot welded lap joints could be effectively and systematically rearranged by strain energy density at the edge of nugget.

• 한국생산제조학회지
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• 제20권6호
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• pp.679-684
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• 2011

Recently, STS 301L joints of side panels to frames for stainless steel rolling stock have been made out by using existing welding methods including Resistance Spot Welding, Laser Welding and Arc Welding. Most of the processes were jointed by spot welding because it is faster at welding and comparatively less expensive for investment in welding facilities than other methods. During spot welding, however, indentation of the metal surface was made due to pressure and melting property of welding. Moreover, since the melting metal was forced to periphery of the plate as indentation was made, sheet separation, which cracked apart between jointed sheets, was carried out. A slight deformation which resulted from sheet separation deteriorated the emotional quality of railway vehicles. This paper suggests that by processing conventional spot electrode tip appropriately, melting metal is able to push up around the processed part (Hollow Spot Electrode Tip) and prevent from being dislodged from first place to periphery. Consequently, sheet separation is remarkably decreased. Also, the emotional quality of appearance of stainless steel rolling stock is enhanced considerably.

• 한국산학기술학회논문지
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• 제7권3호
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• pp.314-318
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• 2006

본 연구에서는 점 용접된 박판이 파괴되어 가는 동적 과정을 시뮬레이션 함으로서 그 점용접부의 강도를 해석하는데 있다. 위판이 아래의 판에 대하여 늘어난 후 0.64 ms가 경과된 시점에서 서로 점 용접된 위판 및 아래 판이 떨어져 나감을 알 수 있다. 비교적 위판 및 아래 판 가운데의 용접 부위에서 최대의 von Mises 응력을 나타내고 있다. 용접이 깨어지는 시점인 0.64 ms 부근에서는 그 내부에너지가 상당히 감소되고 운동에너지는 급격히 증가됨을 알 수 있다. 미끄럼 에너지는 시간이 경과됨에 따라 계단형으로 감소되어 경과 시간이 0.2 ms 부근에서 0이 되다가 그 후로는 미끄럼 에너지가 음수의 값이 되어 두 판들은 오히려 고착이 되는 것을 알 수 있다.

• Journal of Welding and Joining
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• 제16권2호
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• pp.84-92
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• 1998

On this study, the variations of hardness and microstructure were observed at he spot-welded part of 5182 alminum alloy sheets with thickness of 1.2 mm. The hardness of spot-welded part of aluminum alloy indicated the lowest value at nugget center. Also, the position where fatigue crack exists was investigated by surveying microstructure of the spot-welded sections. Mean load-deformation diagrams were obtained from static tensile test. Fracture was occurred completely within 5 mm after transforming elastic into plastic area. Fatigue test was stopped when the specimens of fatigue test had the final displacement of 0.2mm and measured fatigue bending angle and crack length. This study utilized them, investigated the relations between fatigue bending angle and fatigue crack length and made a estimation of the fatigue fracture life of resistance spot welded part of 5182 aluminum alloy sheet. The relative equation o fatigue crack length and fatigue failure life can be represented by {TEX}$L_{C}${/TEX}=α{TEX}$N_{f}^ {β}${/TEX}.

• Tribology and Lubricants
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• 제26권6호
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• pp.341-345
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• 2010

The NAUT(Non contact Air coupled Ultrasonic Testing) is one of the ultrasonic wave inspection methods. It compensates High power ultrasound Pulser Receiver, pre-amp, air probe of high sensitivity in air to generate loss energy by NAUT methods. Generally, in case of ultrasound inspection, it applies contact methods by using couplant. However it can inspect of UT without couplant by this NAUT. The ultrasound transmission reception is composed in stable condition in NAUT. It can inspect high low material or the specimen of rough part, the narrow spot, too. The spot welding is applying the inosculation of automobile component, car body, all boards. The CFRP is necessity of NDE because of the solidity changes material according to lamella tearing. Therefore it checked on realization whether and commercialization in the spot welding and CFRP inspection that the NAUT would be applied them.

• Journal of Welding and Joining
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• 제30권3호
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• pp.66-70
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• 2012

Welding is an essential process in the automotive industry. Most welding processes that are used for auto body is spot welding. And $CO_2$ arc welding is used in a small part. In production field, $CO_2$ arc welding process is decreased and spot welding process is increased due to welding quality is poor and defects are occurred in $CO_2$ arc welding process frequently. But $CO_2$ arc welding process should be used at robot interference parts and closed parts where spot welding couldn't. $CO_2$ welding is divided into lap welding and plug arc spot welding. In case of plug arc spot welding, burn through and under fill were caused in various welding environment such as different thickness combinations of base metal, teaching point, over the two steps welding and inconsistent voltage/current. It makes some problem like poor quality of welding area and decrease the productivity. In this study, we will evaluate the effect of teaching point through the weld pool behavior and bead geometry in the arc spot welding at the plut hole. Welding position is horizontal position. And galvanized steel sheet of 2.0mm thickness that has plug hole of 6mm diameter was used. Teaching point was changed by center, top, bottom, left and right of the plug hole. At each condition, the phenomenon of weld pool behavior was confirmed using a high-speed camera. As the result, we find the center of plug hole is the most optimal teaching point. In the other teaching point, under fill was occurred at the plug hole. This phenomenon is caused by gravity and surface tension. For performance of arc spot welding at the plug hole, the teaching condition should be controlled at a center of plug hole.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.199-202
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• 2007

The center floor is a part of underbody of cars. The assembling method is mostly a resistant spot welding. But the resistant spot welding has many demerits in productivity such as low welding speed, large spatter occurring, hard to verify the welding quality. The laser welding has many merits such as high welding speed, high static and dynamic weld strength. So the laser welding has been studied to substituted the resistant spot welding. Therefore, in this study, as a pre-evaluation stage for replacing the resistance spot welding with laser in production of automobile parts, the weldability of cold rolled and zinc coated steel sheets is studied and also evaluated the weld strength by the tensile shear test. And the shape of weld bead appearances and micro structure of the weld bead section is also evaluated.

• 한국공작기계학회논문집
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• 제14권5호
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• pp.74-79
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• 2005

Spot welding widely used in automotive and aerospace industries has made it possible to produce more precise and smaller electric part by robotization and systemization of welding process. The quality of welding depends upon the size of nugget between the overlapped steel plates. Recently, the thickness of the steel plates becomes much thinner and hence, it introduces the smaller size of nugget. Therefore, it is necessary to develop the criterion to evaluate the quality of weld in order to obtain the optimal welding conditions for the better performance. In this paper, a thin steel plates, 0.1mm through 0.3mm thickness, have been spot-welded at different welding conditions and the nugget sizes are examined by defocused scanning microscopy. The relationships between nugget sizes and weldability have been investigated experimentally. The result of ultrasonic technique shows the good agreement with that of the tensile test.

• Journal of Welding and Joining
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• 제33권6호
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• pp.13-20
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• 2015

Many automotive companies are endeavoring to improve the quality of resistance spot welding by updating body-in-white (BIW) production line with adaptive control spot welding system to compensate the process disturbances such as gap, electrode wear, oxidized surfaces, poor fit up and adhesive etc. Most of the commercial adaptive weld controllers require proper "Initial Welding Schedule" or "Reference weld" to achieve compensation in welding parameters during real time welding. In this study, the compensation of a commercial adaptive weld controller had been observed and analyzed thoroughly for various process disturbances to find optimal initial welding schedule. It was observed that 90 percent of the expulsion current in constant current control as reference welding schedule conferred the maximum button diameter in adaptive control welding. Finally, effects of each disturbance in combined field disturbances system with adaptive control had also been confirmed with the design of experiment (DOE) by minitab(R)16 for combined disturbances situation and suitability of optimum initial weld current had also established with real body part validation test.