• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.11a
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• pp.27-41
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• 1996

In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered, self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI 304 stainless steel and compared with the experimental results.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.63-65
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• 2006

The paper deals with the effect of hydrogen or helium in argon as a shielding gas on GTA welding of austenitic stainless steel. The studies were carried out in GTA(Gas Tungsten Arc) welding with a non-consumable electrode in case with different volume additions of hydrogen or helium to the argon shielding gas, i.e $5%H_2,\;10%H_2$, 30%He and 67%He. The penetration, welding voltage, microstructure and mechanical property were examined. The deepest penetration was obtained from the sample which was welded under shielding gas of $10%H_2$. The studies showed that hydrogen or helium addition to argon changes the static characteristic of the welding arc. The hydrogen or helium addition to argon increases arc power and the quantity of the material melted. The weld metal penetration depth and its width increased with increasing hydrogen or helium content. Additionally, welding voltage increased with increasing hydrogen or helium content.

• Journal of Welding and Joining
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• v.26 no.2
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• pp.62-68
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• 2008

Effects of gravitational orientation on gas tungsten arc welding (GTAW) for 304 stainless steel were studied to determine the critical factors for weld pool formation, such as weld surface deformation and weld pool shape. This study was accomplished through an analytical study of weld pool stability as a function of primary welding parameters (arc current and arc holding time), material properties (surface tension and density), and melting efficiency (cross-sectional area). The stability of weld pool shape and weld surface deformation was confirmed experimentally by changing the welding position. The arc current and translational velocity were the major factors in determining the weld pool stability as a function of the gravitational orientation. A 200A spot GTAW showed a significant variation of the weld pool formation as the arc held longer than 3 seconds, however the weld pool shape and surface morphology for a 165A spot GTAW were 'stable', i.e., constant regardless of the gravitational orientation. The cross-sectional area of the weld (CSA) was one of the critical factors in determining the weld pool stability. The measured CSA ($13.5mm^2$) for the 200A spot GTAW showed a good agreement with the calculated CSA ($14.9mm^2$).

• Journal of Welding and Joining
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• v.28 no.4
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• pp.73-80
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• 2010

In this work, the effect of welding variables on weldability of gas tungsten arc(GTA) welding was investigated with experimental analysis for a commercial pure(CP) titanium (Grade.1). The GTA welding tests on sheet samples with 0.5mm in thick were carried out at different process variables such as arc length, welding speed and electrode shape. In order to search an optimum arc length with full penetration, bead- on-plate welding before butt-welding were performed with different arc length conditions. From the bead- on-plate welding results, the optimum condition considering arc stability and electrode loss was obtained in the arc length of 0.8mm. Butt-welding tests based on the arc length of 0.8mm were carried out to achieve the optimum conditions of welding speed and electrode shape. Optimum conditions of welding speed and electrode shape were suggested as 10 mm/s and truncated electrode shape, respectively. It was successfully validated by the microstructural observation, tensile tests, micro-hardness tests and formability tests.

• Journal of Welding and Joining
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• v.21 no.6
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• pp.20-25
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• 2003

Various welding methods such as Gas Tungsten Arc Welding(GTAW), magnetic force electrical resistance welding and Laser Beam Welding(LBW) are now available for end cap closure of nuclear fuel rods. Even though the resistance and GTA welding processes are widely used in manufacturing commercial fuel rods, they can not be recommended for the remote seal welding of fuel rods in the hot cell Facility due to the complexity of the electrode alignment, the difficulty in replacing parts in a remote manner and the large heat input for the thin sheath. Therefore, the Nd:YAG laser system using optical fiber transmission was selected for the end cap welding of irradiation fuel rods in the hot cell. The remote laser welding apparatus in the hot cell Facility was developed using a pulsed Nd:YAG laser of 500 watt average power with an optical fiber transmission. The weldment quality such as microstructure and mechanical strength was satisfactory. The optimum conditions of laser welding for encapsulating irradiation fuel rods in the hot cell were obtained.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.89-93
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• 2002

A study of noticeable improvement in welding speed in thin-plate Type 304 stainless steels gas tungsten arc (GTA) welding was investigated. The welding speeds were increased to more than 3m/min, up to 8m/min. During the welding, Direct Current Straight Polarity (DCSP) and pulsed current GTA welding processes were carried out, respectively. The appropriate high speed welding parameters were established while achieving a high quality weld. After this, Erichsen test and tensile test were performed. The results obtained wert summarized as following: ultra high speed welding for thin-plate Type 304 could be satisfactorily welded with high speed from 3m/min to 8m/min in both DCSP and pulsed GTA welding; Increasing welding speed was found to decrease the ductility, tensile strength md elongation of welded joint; The optimal frequency would be 200Hz-500Hz for high speed welding in pulsed current welding; DCSP welding could obtain the better results of Erichsen test and tensile test than those of pulsed current welding obtained.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.144-145
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• 2007

Magnesium alloys are the lightest in commercial alloys. Also, they have high damping capacity and the shielding effect of electromagnetic waves. Recently, magnesium alloys have received considerable attention from the transportation industry. Many manufacturers of cars try to increase the use of magnesium alloys in their product. In order to evaluate the weldability of magnesium alloy, gas-tungsten arc welding(GTAW) have been applied to the AZ31, AZ61 and AZ91 alloys and established the optimum welding conditions.

• Journal of Welding and Joining
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• v.20 no.2
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• pp.71-76
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• 2002

Currently knowledge of strain in welds has mainly been obtained from strain gage method; that is directly attaching the gage to the most of the material. The very flew non-contact methods are still in the early stage. One of the non-contact methods is by the use of the laser that has high-level of the accuracy for the measurement, and this laser also has excellent characteristics on which many studies for its applications are focused throughout the many fields. The paper is on the measurement of the strain caused by the characteristics and the temperature changes of the GTA welded zone employed with 3D ESPI system that is functionally modified through the laser ESPI system. This system may be applied the steel plate such as for the electronics, chemistry, flood instrument and electronic appliances.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.123-124
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• 2006

This study aimed at exploiting low heat input characteristic of laser welding to effectively control grain coarsening in the fusion zone(FZ) and heat affected zone(HAZ) of 1.5mm thick 18wt% Cr ferritic stainless steel weld. The study demonstrated that as compared with gas tungsten arc welding(GTAW), laser welding brought about significant grain refinement in the FZ and HAZ. However, the impact absorbed energy of GTA weld was superior than that of laser weld because the strengthening effect during welding and cooling stage was higher In laser weld than that in GTA weld. The coarser grains in each weld than base metal resulted in an inferior toughness.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.176-178
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• 2004

Gas tungsten arc welds on Al-4 wt% Cu alloys were investigated to determine effects of gravitational orientation on the weld solidification behavior. Outward convection flows in the parallel-down weld might be inhibited because of its reverse direction with respect to the gravity vector. This resulted in abnormal 'S' shape of the trailing s-1 interface and the solidification rate (Vs), which was receded toward the weld pool center. Significant influence of gravitational orientation resulted in the variation on the weld pool shape associated with convection flows, which in turn affected solidification orientation/morphology and the primary dendrite spacing(λ$_1$).