• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.575-583
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• 1991

The weld pool convection problem that occurs during the stationary GTA welding has been studied, considering the four driving forces for weld pool convection, i.e., the electromagnetic force, the buoyancy force, the aerodynamic drag force, and the surface tension force at the weld pool surface. In the numerical simulation, the difficulties associated with the irregular moving liquid-solid interface have been successfully overcome by adopting a Boundary-Fitted Coordinate system. In the experiments to show the validity of the numerical analysis, a deep periphery and shallow centerpentrated weld pool shape was observed from the etched specimen. It could be revealed that this type of weld pool shape could be simulated, only when some of aerodynamic drag force distributions are considered. Although slight disagreement arose, the calculated and the observed weld pool shapes were in a reasonable agreement.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.746-751
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• 2002

In order to make clear the physical relation among the arc plasma, the anode heat transfer and the weld penetration, the results of experimental measurements of temperatures of arc plasma, the distributions of heat input and current on the anode and the weld penetration were presented The experimental results showed that the electron temperature above the anode and current and heat input density on the anode was dominated by the position of the cathode. Furthermore, it was showed that electron temperature of arc plasma was dominated by the cathode shape. These results were related with the results of the welded penetration measurements. As a result, it was showed that the electron temperature above the anode and current density distribution on the anode decided the heat input density distribution on the anode and that the heat input density on the anode remarkably dominated the size of the weld penetration in argon GTA welding process. Furthermore, it was suggested that the cathode played the important role in the determination of the weld penetration in argon GTA welding process.

• Journal of Welding and Joining
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• v.5 no.4
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• pp.36-46
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• 1987

The impact toughness and SCC resistance of duplex stainless steel weldment made by GTAW, GMAW and SMAW processes was studied. The impact toughness of GTA weld metal was higher than that of GMA weld metal which contained more ferrite phase than GTA weld metal. The impact toughness of SMA weld metal was the lowest due to the harmful effect of inclusions inspite of richness of more ductile austenite phase. From these facts, it can be concluded that the important factors determining the weld metal toughness were the amount of ferrite phase and the cleaness of weld metal. While the SCC resistance of SMA weld metal was lower than that of base metal and nay other weld metal, the SCC resistance of GMA and GTA weld metal was higher than that of base metal but that of all the HAZ's were lower than that of base metal. Therefore, the impact toughness and SCC resistance of GTA and GMA weldment was pretty good as long as phase ratio was propertly controlled. Although the phase ratio was controlled, SMA weld metal could not get a good combination because the lack of shielding from the environment results in a high content of inclusions in weld metal.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.57-63
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• 2012

The purpose of this study is to evaluate the welding distortion of the circular type lap joint in STS304L of 0.7mm thickness by using FEA. In order to do it, a heat input model for GTA welding process with non-consumable electrode was established through comparing the molten pool shapes and temperature distributions obtained by both FEA and experiment. With the heat input model, the welding distortion of the circular type lap joint was evaluated by 3-D FEA. From FEA results, it was found that 3-D FEA with proper heat input model can be used for the evaluation of the excessive distortion of the circular type lap joint of STS304L thin plate. In addition, the root cause of the excessive distortion in the weld was also identified as the excessive compressive residual stress in the tangential direction of the weld.

• Journal of Welding and Joining
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• v.32 no.1
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• pp.53-60
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• 2014

The automatic arc welding is generally accepted as the preferred joining technique and commonly chosen for assembly of large metal structures such as in areas of automotive, aircraft and shipbuilding due to its joint strength, reliability, and low cost compared to other joint processes. Recently, several mathematical models have been developed and studied for control and monitoring welding quality, productivity, microstructure and weld properties in arc welding processes. This study indicates the prediction of process parameters for the expected welding quality with accordance to the adaptive GTA welding process. Furthermore, the mathematical models is also develop to aid the selection of an optimal welding process as the generation of process controls to predict the bead geometry as a function output parameters in the GTA welding process. The developed models through this study showed comparatively excellent predicted results, and will extend to other welding processes to integrate an optimized system for the robotic welding process.

• Journal of Welding and Joining
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• v.25 no.5
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• pp.64-71
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• 2007

The aim of this paper is to investigate the effects of welding parameters on the weld shape in seal-welding of STS304L capsule for manufacturing a radioisotope source which is widely used in nondestructive testing of metal structures using gamma ray. Pulsed gas tungsten arc (Pulsed GTA) welding is performed for thin cross sectional area of the capsule. Seven welding parameters including current waveform parameters and arc length etc. are selected as main process parameters using design of experiment. The weld shape such as bead width, penetration depth, weld area, aspect ratio and area rate is investigated to assess the effects of welding parameters. As results, the combination of pulse duty/welding speed largely affects on bead width, penetration depth, area and aspect ratio. Finally, it is concluded that the key parameters are the combination of pulse duty/welding speed, base current and arc length, and their optimal conditions are 50%/1.77mm/s, 6.4A and 1 mm.

• Journal of Welding and Joining
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• v.5 no.4
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• pp.12-21
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• 1987

To investigate the suitability of nitrogen gas as an internal purging gas, various properties of GTA welded joints of duplex, 316L stainless steel, Cu-Ni alloy pipe using nitrogen purging gas were evaluated with reference to onew purged with argon gas. Mechanical properties evaluated by the tensile, bending test, and hardness value of welded joints with nitrogen gas purging did not show any difference those with argon gas. General and local corrosion rates of each welded joint prepared by nitrogen gas purging also showed no difference with those prepared by argon gas. Based on the present test results it is confirmed that nitrogen is a suitable purging gas for GTA welding of stainless steels and nonferrous piping systems, which can be used at lower cost instead of argon.

• Journal of Welding and Joining
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• v.28 no.2
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• pp.27-31
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• 2010

Generally, angle pieces at the corners of cargo tank of membrane type LNG carrier ship are manually welded, due to their various shapes and positions. In this study, a GTA welding robot system was developed in order to improve productivity, which consists of a 7-axis manipulator, a system controller, a GTA welding power source, and peripheral devices. The welding system is characterized by capabilities of welding corrugated work pieces as well as 90/135 degree linear work pieces, and controlling the entire weld cycle automatically. The developed system was field tested on actual work pieces and its performance was proven to be successful.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.4-8
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• 2014

In this research, GTA overlay welding system is developed for inside of straight pipes in various diameter. It can be applied to oil, ship building and plant industry, especially pipes connected to pressure vessels, for the purpose of cost reduction by cladding inside of pipes with corrosion and heat resistant alloys such as stainless steel or Inconel. Developed system consists of GTA power source, torch, wire feeding system, automatic arc length adjusting device, CCD camera and cooling unit. Two types of pipe inside overlay welding system are developed. One is for maximum 3m pipe length with 3 inch ~ 12 inch pipe outer diameter. Another type can be applied to maximum 12m pipe length with 7 ~ 24 inch OD. Developed system successfully produced inside cladded pipe and the results are shown through cross sectional images of the pipes.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.59-69
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• 2000

The purpose of the present study was to investigate weld metallurgical phenomena such as primary solidification mode, microstructural evolution and hot cracking susceptibility in nitrogen-bearing austenitic stainless steel GTA welds. Eight experimental heats varying nitrogen content from 0.007 to 0.23 wt.% were used in this study. Autogenous GTA welding was performed on weld coupons and the primary solidification mode and their microstructural characteristics were investigated from the fusion welds. Varestraint test was employed to evaluate the solidification cracking susceptibility of the heats and TCL(Total Crack Length) was used as cracking susceptibility index. The solidification mode shifted from primary ferrite to primary austenite with an increase in nitrogen content. Retained delta ferrite exhibited a variety of morphology as nitrogen content varied. The weld fusion zone exhibited duplex structure(austenite+ferrite) at nitrogen contents less than 0.10 wt.% but fully austenitic structure at nitrogen contents more than 0.20 wt.%. The weld fusion zone in alloys with about 0.15 wt.% nitrogen experienced primary austenite + primary ferrite solidification (mode AF) and contained delta ferrite less than 1% at room temperature. Regarding to solidification cracking susceptibility, the welds with fully austenitic structure exhibited high cracking susceptibility while those with duplex structure low susceptibility. The cracking susceptibility increased slowly with an increase in nitrogen content up to 0.20 wt.% but sharply as nitrogen content exceeded 0.20 wt.%, which was attributed to solidification mode shift fro primary ferrite to primary austenite single phase solidification.