• 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.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.98-103
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• 2008

This paper is to discuss distribution of welding residual stresses of a ferritic low alloy steel nozzle with dissimilar metal weld using Alloy 82/182. Two dimensional (2D) thermo-mechanical finite element analyses are carried out to simulate multi-pass welding process on the basis of the detailed and fabrication data. On performing the welding analysis generally, the characteristics on the heat input and heat transfer of weld are affected on the weld residual stress analyses. Thermal analyses in the welding heat cycle process is very important process in weld residual stress analyses. Therefore, heat is rapidly input to the weld pass material, using internal volumetric heat generation, at a rate which raises the peak weld metal temperature to $2200^{\circ}C$ and the base metal adjacent to the weld to about $1400^{\circ}C$. These are approximately the temperature that the weld metal and surrounding base materials reach during welding. Also, According to the various ways of appling the weld heat source, the predicted residual stress results are compared with measured axial, hoop and radial through-wall profiles in the heat affected zone of test component. Also, those results are compared with those of full 3-dimensional simulation.

• Journal of Welding and Joining
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• v.28 no.5
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• pp.86-92
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• 2010

In GMAW processes, bead geometry is a criterion to estimate welding quality. Bead geometry is affected by welding current, arc voltage, welding speed, shielding gas and so on. Thus the welding condition has to be selected carefully. In this paper, an experimental method for the selection of optimal welding condition was proposed in the root pass welding which was done along the GMA 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. Through the experiments, the target values of the back bead width and the height were chosen as 4mm and 1mm respectively for the V-grooved butt weld joint. From a series of welding test, it was revealed that a uniform weld bead can be obtained by adopting the optimal welding condition which was determined according to the method proposed.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.127-128
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• 2007

To investigate mechanical property on the low temperature plate weld metal, the two different plates of the same steel grade were welded and evaluated on the multiple pass welds and both side one run welds with different Mo contents welding consumables. The results are summarized as follows; 1) Welds made by no Mo containing wire showed very low impact values for type of material company. 2) Welds made by 0.25%Mo containing wire showed good impact value regardless of both side one run welds and multiple pass welds. 3) Welds made by 0.5%Mo containing wire showed good impact value for both side one run welds, while it was not acceptable value for multiple pass welds.

• Journal of Welding and Joining
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• v.11 no.3
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• pp.34-47
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• 1993

Finite element models were developed for thermal and residual stress analysis for the specific welding problems. They were used to evaluate the effectiveness of the various welding heat input models, such as ramp heat input function and lumped pass models. Through the parametric studies, thermal-mechanical modeling sensitivity to the ramp function and lumping techniques was determined by comparing the predicted results with experimental data. The kinetics for residual stress formation during welding can be developed by iteration of various proposed mechanisms in the parametric study. A ramp heat input function was developed to gradually apply the heat flux with variable amplitude to the model. This model was used to avoid numerical convergence problems due to an instantaneous increase in temperature near the fusion zone. Additionally, it enables the model to include the effect of a moving arc in a two-dimensional plane. The ramp function takes into account the variation in the out of plane energy flow in a 2-D model as the arc approaches, travels across, and departs from each plane under investigation. A lumped pass model was developed to reduce the computation cost in the analysis of multipass welds. Several weld passes were assumed as one lumped pass in this model. Recommendations were provided about ramp lumping techniques and the optimum number of weld passes that can be combined into a single thermal input.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.14-23
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• 2007

Welding fabrication invariantly involves three district sequential steps: preparation, actual process execution and post-weld inspection. One of the major problems in automating these steps and developing autonomous welding system is the lack of proper sensing strategies. Conventionally, machine vision is used in robotic arc welding only for the correction of pre-taught welding paths in single pass. However, in this paper, multipass tracking more than single pass tracking is performed by conventional seam tracking algorithm and developed one. And tracking performances of two algorithm are compared in multipass tracking. As the result, tracking performance in multi-pass welding shows superior conventional seam tracking algorithm to developed one.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.71-76
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• 2013

Gas nitriding is a surface hardening process where nitrogen is introduced into the surface of a ferrous alloy. During fusion welding of nitrided carbon steel, the nitride inside weld metal is dissolved and generates nitrogen gas, which causes porosities - blow holes and pits. In this study, several laser welding processes such as weaving welding, two-pass welding, dual beam welding and laser-arc hybrid welding were investigated to elongate the weld pool to enhance nitrogen gas evacuation. The surface pits were successfully eliminated with elongated weld pool. However blowholes inside the weld metal were effective reduced but not fully disappeared.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.83-84
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• 2008

The primary water stress corrosion cracking (PWSCC) of dissimilar metal weld based on Alloy 82/182 is one of major issues in material degradation of nuclear components. It is well known that the crack initiation and growth due to PWSCC is influenced by material's susceptibility to PWSCC and distribution of welding residual stress. Therefore, modeling the welding residual stress is of interest in understanding crack formation and growth in dissimilar metal weld. Currently in Korea, a numerical round robin study is undertaken to provide guidance on the welding residual stress analysis of dissimilar metal weld. As a part of this effort, the present paper investigates distribution of welding resisual stress of a ferritic low alloy steel nozzle with dissimilar metal weld using Alloy 82/182. Two-dimensional thermo-mechanical finite element analyses are carried out to simulate multi-pass welding process on the basis of the detailed design and fabrication data. The present results are compared with those from other participants, and more works incorporating physical measurements are going to be performed to quantify the uncertainties relating to modelling assumptions.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.6
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• pp.71-78
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• 2007

There have been continuous efforts to automate welding processes. This automation process could be said to fall into two categories, weld seam tracking and weld quality evaluation. Recently, the attempts to achieve these two functions simultaneously are on the increase. For the study presented in this paper, a vision sensor is made, and using this, the 3 dimensional geometry of the bead is measured in real time. For the application in welding, which is the characteristic of nonlinear process, a fuzzy controller is designed. And with this, an adaptive control system is proposed which acquires the bead height and the coordinates of the point on the bead along the horizontal fillet joint, performs seam tracking with those data, and also at the same time, controls the bead geometry to a uniform shape. A communication system, which enables the communication with the industrial robot, is designed to control the bead geometry and to track the weld seam. Experiments are made with varied offset angles from the pre-taught weld path, and they showed the adaptive system works favorable results.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.88-96
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• 1999

The effects of root gap on welding residual stress and deformation are dealt with the multi-pass weldment with three kinds(0, 6, 30mm) of root gap by F.E.M common code, and then compared with experiment data. In this analysis, an 100% ramp heat input model was used to avoid numerical convergence problem due to an instantaneous increase in temperature near the fusion zone, and the effect of a moving arc in a two dimensional plane was also included. During the analysis, a small time increment was applied in a period with instantaneous temperature fluctuation while a large time increment was used in the rest period. The residual stress is distributed as symmetric types and maximum value is also equivalent when the weldment with 0mm and 6mm root gap is welded. In the case of 30mm root gap welding, the distribution of the residual stress extends over a wide range as asymmetric types due to the built-up weld, and most of the residual stress is biased in the side of a built-up weld part. In case of 0mm gap welding and 6mm gap welding, a little angular distortion occurs, but the level of deformation is small. When the weldment with 30mm root gap is welded, the angular deformation of the asymmetric types, however, occurs larger than the other specimens. The experimental and the analytic results show good coincidence and indicate that the welding residual stress and deformation distribution of 30 mm root gap specimen may be asymmetric and the amplitude is larger than those of root gap specimen under standard.