• Journal of Power System Engineering
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• v.11 no.1
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• pp.107-114
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• 2007

Underwater wet arc welds were experimentally performed on 11mm thick SS400 mild steel plate as base metal by using six different types of flux coated electrodes of 4.0mm diameter; KSKR, KSKT, USBL, JPUW, UWEA, and UWEB. As results, the developed flux coated underwater electrode had a good weldability compared with other domestic terrestrial electrodes. By rapid cooling rate, the hardness value of HAZ were increased by quenching effects. Mechanical properties for the multi-pass butt-welding specimen are also tested experimentally. The feasibility of the developed underwater electrode was experimentally studied and the results achieved in this wet arc welds have shown that the developed wet welding electrode UWEB can have a degree of integrity.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.693-702
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• 1991

The existence of residual stress in the circumferential butt welded pipes is one of the most important problems concerning stress corrosion cracking in service. In this paper, the residual stress distributions in three kinds of circumferential butt welded pipes were measured by the hole drilling strain gage method and calculation using finite element method is performed and its results are compared with the experiments. At the inner surface of the pipe region near the center line of welding is under high tensile residual stress. However, as the distance from the center line of welding increases, the tensile component decreases and finally becomes compressive residual stress at region far away from the center line of welding. The longitudinal residual stress at the outer surface is compressive regardless of the diameter of pipe and the circumferential stress is changed rom compressive to tensile as pipe diameter increases. The results also demonstrate that the residual stress is mainly caused by self restraint bending force in the pipe welding.

• Journal of Welding and Joining
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• v.27 no.1
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• pp.95-101
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• 2009

In case of manufacturing the high quality welds or pipeline, the full penetration weld has to be made along the weld joint. Thus the root pass welding is very important and has to be selected carefully. In this study, an experimental method for the selection of optimal welding condition was proposed in the root pass welding which was done along the V-grooved butt weld joint. This method uses the response surface analysis in which the width and height of back bead were chosen as the quality variables of the weld. The overall desirability function, which is the combined desirability function for the two quality variables, was used as the objective function for getting the optimal welding condition. In the experiments, the target values of the back bead width and the height are 6mm and zero respectively for the V-grooved butt weld joint of 8mm thickness mild steel. The optimal welding conditions could predict the back bead profile(bead width and height) as 6.003mm and -0.003mm. From a series of welding test, it was revealed that a uniform and full penetration weld bead can be obtained by adopting the optimal welding condition which was determined according to the method proposed.

• Journal of Welding and Joining
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• v.31 no.2
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• pp.57-62
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• 2013

Magnesium has good castability and limited workability, so its products have been manufactured by almost casting processes. In this study, a pulsed Nd:YAG laser was used to butt-weld the sand casting magnesium alloys. And the effect of welding conditions such as peak power, pulse width, welding speed was evaluated in detail. As a result of this study, large underfill and plenty of spatter taken place under the conditions with high peak power. Thus, it is recommended to use low peak power and long pulse width to obtain good welds with deep penetration. It is also confirmed that the welding speed and pps(pulse per second) are directly connected at weld defects such as underfill, porosity.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.5
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• pp.53-64
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• 2012

Deep and narrow welds can be produced by laser welding at high welding speeds with a narrow heat-affected zone (HAZ) and little distortion of the workpiece. This study aims to evaluate the usefulness of laser welding at automobile component manufacture. Microstructure observation, hardness test, tensile test and fatigue life test are performed by using the fiber laser welded SPFC590 steel sheets which is used widely in the manufacture of automotive seat frame. Three kinds of specimens are only a SPFC590 steel plate, quasi-butt joint plate and lap joint plate by laser welding. The following results that will be helpful to understand the static strength, fatigue crack initiation and growth mechanism were obtained. (1) The tensile strength of quasi butt joint specimens nearly equal to base metal specimens, but lap joint specimens fractured in shear area of weld metal. (2) The fatigue strength of quasi-butt joint specimen was approximately 8 percent lower than that of the base metal specimens. Furthermore, the lap joint specimens were less than 86 percent of the base metal specimens. (3) The lap joint fatigue specimens fractured at shear area in high level stress amplitude, while fractured at normal area in low level stress amplitude. From these results, the applicability of the laser welding to the automobile component is discussed.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.301-306
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• 2002

This paper presents the use of the neural network technology to establish a mathematical model for predicting bead geometry (top-bead width, top-bead height, back-bead width and back-bead height) for multi-pass welding, and understand relationships between process parameters and bead geometry for robotic GMA welding process. Using a series of robotic arc welding, additional multi-pass butt welds were carried out in order to verify the performance of the developed neural network model. The results show that not only the proposed model can predict the bead geometry with reasonable accuracy and guarantee the uniform weld quality, but also the neural network model could be better than the linear and curvilin ear equations developed from Lee [8].

• Journal of Welding and Joining
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• v.34 no.5
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• pp.47-53
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• 2016

The aim of this study is to consider effect of weld elastic modulus on simulations of stress concentration and fatigue life for pressure vessel. The investigations include analysis with ADINA and WINLIFE softwares for whole body model about using condition of the boiler vessel. Values of weld elastic modulus were divided by 5 steps in butt weld area of the boiler vessel body. The stress concentration of the butt weld more was increased in case of higher elastic modulus of weld area because of higher difference of material properties between matrix and weld. It was concluded that the fatigue lives were decreased along increasing stress concentration due to high elastic modulus of weld. The matrix microstructure was estimated as pearlitic structure of ${\alpha}$ ferrite and pearlite. And the microstructures of welds along 5 steps of elastic modulus were estimated as bainitic fine pearlite and martensite as increasing elastic modulus.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.910-914
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• 2012

In constructing all kinds of equipment and steel structures, discontinuous areas such as weld defects formed in a welded structure tend to generate cracks that will result in damage. In this study, ATOS high-strength steel welding becomes important in butt welding where the tensile strength of the steel is over 80kg/$mm^2$. Structural discontinuities such as joints are more susceptible cracks in part due to their repeated loading and fatigue crack growth. The quality of parts produced depend or the shielded amounts of steel and on the skill of the welders in making strong welds. It is true that there are many factors that can be used to generate a lot of research in this area. However geometry and load conditions due to the combined effects with many issues could be solved through this study. Butt welding material at a plate thickness of 12t in ATOS 80 high-strength steel with a 4 pass, 20l/min, 24V/200A welder is good at making specimens with the quality shown in radiographic testing.

• Journal of the Korean Society for Precision Engineering
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• v.8 no.1
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• pp.41-49
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• 1991

A knowledge of the resdual stress distribution at circumferential weldments can normally increase the accuracy of a fracture assessment in pipe line. In this paper, we present the measurements about the residual stress distributions at three kinds of circumferential butt welded pipes using the holl drilling strain gage method. By this experiment, we have obtined the following characteristics. At the inner surface of the pipe region near the center line of welding is under high tensile residual stress. However, as the distance from the center line of welding increases, the tensile component decreases and finally becomes compressive residual stress at region far away from the center line of welding. The longitudinal residual stress at the outer surface is compressive regardless of the diameter of pipe and the circumferential stress is changed from compressive to tensile as pipe diameter increases. The results also demonstrate that the residual stress is mainly caused by self-restraint bending force in the pipe welding.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.12-17
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• 2001

With the advance of the robotic welding process, procedure optimization that selects the welding procedure and predicts bead width that will be deposited is increased. A major concern involving procedure optimization should define a welding procedure that can be shown to be the best with respect to some standard and chosen combination of process parameters, which give an acceptable balance between production rate and the scope of defects for a given situation. This paper presents a new algorithm to establish a mathematical model f3r predicting bead width through a neural network and multiple regression methods, to understand relationships between process parameters and bead width, and to predict process parameters on bead width for GMA welding process. Using a series of robotic arc welding, additional multi-pass butt welds were carried out in order to verify the performance of the neural network estimator and multiple regression methods as well as to select the most suitable model. The results show that not only the proposed models can predict the bead width with reasonable accuracy and guarantee the uniform weld quality, but also a neural network model could be better than the empirical models.