• Journal of Welding and Joining
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• v.33 no.4
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• pp.50-56
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• 2015

In general, discontinuity of metallurgical and structural points of weld zone could decline the fatigue strength. For the lightweight trend, the AHSS application in automotive chassis is in-progress. However, there are few research reports on AHSS welds fatigue strength in especially automotive chassis parts. Therefore, in this study, we evaluated the effects of the factors affecting the AHSS welding fatigue strength. As the result, the stress concentration of weld bead is the most important factor for welding fatigue strength. For the enhancement of welding fatigue strength, we focused on reducing the stress concentration of the welding beads. So, we applied and proved the plasma welding process and GTAW (Gas Tungsten Arc Welding) dressing method. It was verified by uniaxial fatigue specimen, fatigue performance increased from 40 to 60% by applying TIG dressing method compared to the conventional GMAW (Gas Metal Arc Welding). These results could be recommended the enhancement of fatigue performance of AHSS.

• Journal of Welding and Joining
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• v.10 no.1
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• pp.20-34
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• 1992

Characteristics of two correcting methods, a new Autogeneous GTAW heating (TIG) method and the conventional GMAW bead-on plate welding(MIG) method, for distorted aluminum fabrication structures were studied. As a result of microscopic study of Autogeneous GTAW heating and GMAW bead-on plate welding areas, porosities in weld metal and surface cracks in local heating zone were found. Through the mechanical tests, it was verified that porosities decrease tensile strength and surface of distortion, angular displacement and transeverse shrinkage were measures and compared. In order to investigate changes of material properties in heating area and cause of defects such thermal stresses were calculated by ADINA. Through the computations of transient thermal stresses and microscopic observation of fracture surface, thermal stress was found to be the cause of crack during Autogeneous GTAW heating.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.670-677
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• 2003

Although Gas Tungsten Arc Welding (GTAW or TIG welding) is considered as high quality and precision welding process, it also has demerit of low melting rate. Narrow-gap TIG welding which has narrow joint width reduces the groove volume remarkably, so it could be shorten the welding time and decrease the overall shrinkage in heavy wall pipe welding. Generally Narrow-gap TIG welding is used as orbital welding process, it is important to select the optimum conditions for the automatic control welding This paper looks at the application and metallurgical properties on Narrow-gap TIG welding joint of heavy wall large austenitic stainless steel pipe to determine the deposition efficiency, the resultant shrinkage and fracture toughness. The fracture toughness depends slightly on the welding heat input.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.21-30
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• 2017

Of the marine engine components, the piston crown and exhaust valve are repaired most frequently. These works are conducted through conventional welding processes such as GTAW or SAW, domestically in marine engine repair factories. New high-efficiency welding or overlay processes such as tandem SAW, tandem MAG, hybrid TIG-MIG welding, pulsed-GMAW, CMT welding, and super TIG welding have been developed recently. Moreover, the plasma transfered arc (PTA) process is an efficient spray method for overlaying on the exhaust valve. In this review paper, the new high-efficiency repair welding methods are introduced for marine engine components. The problems due to repair welding for marine engine components are also presented.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.68-74
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• 2016

Adoption of narrow gap welding shall be increased for the butt joint of thick plate, because the deformation and welding cost is reduced by decrease of cross-sectional area. However, sometimes narrow gap causes defects such as lack of fusion since it has small groove angle and narrow groove width. Therefore, GMAW, GTAW and SAW process shall be adopted to narrow gap welding with small bead hight and low deposition rate. In this study, Super-TIG welding using C-type strip was applied to semi-narrow gap butt joint in order to increase the welding productivity. High deposition rate 10kg/hr was obtained by high current 600A without undercut, humping bead and other welding defects. Measuring the mean and standard deviation of the melting depth to evaluate the developed processes, the fusion line type was determined by measuring the difference between maximum and minium melting depth. Furthermore, a model on arch fusion line and linear fusion line was suggested in order to prevent LF on groove wall in narrow gap butt welding.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.26-26
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• 2009

TIG 용접은 고품질이고 용접인자의 제어가 쉽고 정확하다는 장점이 있지만, 얕은 용입과 낮은 생산성과 같은 단점이 있다. TIG 오비탈 용접에서는 용입의 한계 때문에 작은 루트면과 넓은 그루브를 가공하여 다층 용접을 하며, 루트패스에서는 파이프 진원도에 의한 핏업 시 단차의 문제가 자주 발생하여 많은 현장에서 루트갭을 만들어 수동 용접하는 실정이다. 따라서 생산성이 낮으며 생산 단가가 높고 용접 품질이 작업자에 따라 다르게 된다. 이러한 문제점을 해결하여 자동 오비탈 용접을 위해 단차를 흡수 할 수 있는 용접 공정 개발이 필요하다. 본 연구의 목적은 TIG 용접에서 단차에 따른 용접성을 검토하여 이를 맞대기 용접에 적용했을 때 균일한 이면비드를 얻는 공정을 개발하는 것이다. 따라서 본 연구는 아래보기 자세에서 단차에 따른 용입 특성을 이면비드 및 단면으로 비교 분석하였다. 단차 없이 아크길이만 1mm, 2mm, 3mm로 변경하여 실험한 결과 아크길이가 짧아질수록 표면비드 폭은 좁아졌고 이면비드 폭은 증가하는 경향을 나타내어 아크길이가 짧아질수록 용융효율이 증가하는 것을 확인하였다. 단차 1mm에서 아크길이 3mm를 제외하고 표면비드 및 이면비드가 미려하였다. 하지만 단차 2mm에서는 아크길이 1mm, 2mm, 3mm 전부 이면비드가 생성되지 않았다. 이는 단차로 인해 아크길이가 증가하여 용융효율이 낮아졌기 때문이라 판단된다. 이면비드가 생성되지 못한 시험편을 백 베벨링(0.5mm, 1.0mm, 1.5mm, 2.0mm)하여 실험한 결과 단차 2mm, 아크길이 1-3mm 백 베벨링 2.0mm 적용한 시험편에서 양호한 이면비드를 얻을 수 있었다.

• 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.

• Proceedings of the KWS Conference
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• 1998.05a
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• pp.150-154
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• 1998

The purpose of this paper is to investigate optimum welding conditions of STS 304 thin sheet by GTA welding and control 6 $\delta$--fenite which is harmful in mechanical processing, corrosion problem and can be formed brittle a phase in using long term at high temperature. One series of automatic welds was made using argon plus 10, 20, 30 % nitrogen to ensure a fully austenite deposit. Results obtained were summarized as follows: 1) 6 $\sigma$ferrite content in the weld metals is influenced largely by the nitrogen content. 2) Additions of nitrogen to the shielding gas can significantly reduce the amount of retained delta ferrite and result in an increase in hot cracking. 3) Bead width was increased when Ar + $N_2$ shielding gas was used and travel speed was increased. 4) Ar+$N_2$ shielding gas made weld metal ductile and reduce 6 -$\delta$-ferrite.

• Journal of Welding and Joining
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• v.17 no.3
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• pp.50-54
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• 1999

Feasibility study of the application of a developed annealed austenitic stainless steel at cryogenic temperature has been performed for membrane tank of LNG ship. Chemical properties of developed stainless steel are compared with a domestic commercial stainless steel and a foreign stainless steel which are used for LNG ships. Tensile properties at cryogenic temperature and fatigue strength at room temperature are measured for but and lap joints which are TIG welded specimens. Developed stainless steel having a small amount of titanium component shows the finest grain size in the HAZ, compared with the other stainless steel studied. Tensile strength, elongation and fatigue strength of the developed stainless steel are equal to those of the foreign stainless steel studied and are higher than the domestic commercial stainless steel studied.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.5
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• pp.104-113
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• 2006

The main objective of this study is to investigate the effect of compounded welding by using acoustic emission (AE) signals and doing a source location for weld heat affected zone (HAZ) through tensile testing. This study was carried out an SWS 490A high strength steel for electric shield metal arc welding, SMAW; $CO_2$ gas metal arc welding, GMAW($CO_2$); and gas tungsten arc welding, GTAW/TIG. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. For instance, Gutenberg-Richter magnitude-frequency relationship (G-R MFR) offers useful b-value in data analysis. Namely event identification, source location gives the X- and Y-coordinates of the AE source. And K-means clustering analysis by Euclidean distance confirmed that was powerful to source location. Generally, strength of welded metal zone was stronger than strength of base metal. As the result, confirmed certainly that fracture is produced in HAZ instead of welded metal zone from source location.