• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.2
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• pp.51-58
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research works is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stain-stress behavior and the hardness of the welded part are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding qualify is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.36-38
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• 2007

The instability of the arc in the $CO_2$ arc welding affects the quality of the weld in the automotive industry. This paper evaluates the effects of the arc stability in $CO_2$ arc welding with respect to vertical welding positions. In this experiment, galva-annealed steel sheets(CA) were used as specimens, and these materials were welded by adopting new Cold Metal Transfer (CMT) process. For each sample, fillet joint welding trials were carried out using the same conditions. Each part of welding joints was welded with vertical-up, vertical-down position at $45^{\circ},\;90^{\circ}\;and\;135^{\circ}$ degrees. A high speed camera and a welding signal monitoring system were used for monitoring fluid-flow phenomena in weld pools and frequency measurements, respectively. Through this study, the welding position were found to be key factors mainly to influence the arc stability in $CO_2$ welding moreover and that the arc stability in the vertical-up welding position was observed to be more stable than the vertical-down welding position below $90^{\circ}$.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.997-1003
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• 2005

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research works is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding qualify of the cut section, stain-stress behavior and the hardness of the welded part are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and 4m/min of pressure for shielding gas.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.3
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• pp.282-292
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• 2007

The present paper describes the results of high speed photography, acoustic emission (AE) detection and plasma light emission (LE) measurement during $CO_2$ laser welding of 304 stainless steel in different processing conditions. Video images with high spatial and temporal resolution allowed to observe the melt dynamics and keyhole evolution. The existence of keyhole was confirmed by the slag motion on the weld pool. The characteristic frequencies of flow instability and keyhole fluctuations at different welding speed were measured and compared with the results of Fourier analyses of temporal AE and LE spectra. The experimental results were compared with the newly developed numerical model of keyhole dynamics. The model is based on the assumption that the propagation of front part of keyhole into material is due to the melt ejection driven by laser induced surface evaporation. The calculations predict that a high speed melt flow is induced at the front part of keyhole when the sample travel speed exceeds several 10 mm/s. The numerical analysis also shows the hump formation on the front keyhole wall surface. Experimentally observed melt behavior and transformation of the AE and LE spectra with variation of welding speed are qualitatively in good agreement with the model predictions.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.39-44
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• 2003

The welded specimens were made by butt welding of the 2 wires of 50mm length using the pulsed YAG laser. The laser welded wires were tested for investigating the shape memory effect and the ability of super elasticity. The fatigue properties of the welded wires were investigated using the rotary bending fatigue tester specially designed for wires. Moreover, the effect of defocusing distance during laser welding on the static and fatigue properties was Investigated. The shape memory effect and super elasticity of the laser welded wires were approximately identical with that of base metal at the test temperature below 353K. However, the welded wires were broken within elastic limit at the test temperature above 353k. Under the cyclic bending loading conditions, the welded wires could be useful only below the elastic limit, while the base metal had sufficient fatigue life even the stress induced M-phase region. The fatigue strength of the welded wires was about half of that of the base metal. The deterioration of the static and fatigue properties in the welded wires was proven to be from the large difference of the transformation behavior between the base metal and welded part that is caused by vaporization of Ni-content at the welded part during the welding process. The defocusing distance below 3mm acted more largely on lowering the strength of the welded wires than that of 6mm or 8mm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.853-854
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• 2012

• Plant Journal
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• v.4 no.2
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• pp.66-72
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• 2008

In this inquiry, I would suggest jet ventilation system for effective elimination of welding flaw at machinery material welding shop on plant and evaluate the airstream on inner space and property of welding flaw's density through the examination. We can know outer atmosphere inflows at the speed of about 0.05m/s from western entrance in case of stopping the jet ventilation system, but airstream is accumulated on entire space. At height of worker's breathing surface(Ground Level = 1.5 m, below of GL) and welding work center, density of welding flaw on upper part(GL = 12m) is appeared 4 times higher than outer atmosphere at surplus range besides nearby of western entrance. At operation of jet ventilation system, since the smooth air current transfer at inner space and exhaust effect the wind speed is maintained at 0.932 m/s at the point of height of worker's breathing surface on inner space and it's concluded about the working conditions have been better than before operation of jet ventilation system because of that results show that inner space density of welding flaw at height of worker's breathing surface is 40.5%, and in the work shop, it is 20.3% at upper part.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.1
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• pp.96-102
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• 2007

Welding deformation causes critical problems under construction and in use of steel structures by varying the magnitude of the steel structures and deteriorating mechanic strength. Existing method to construct steel structures in civil engineering needs preassembly process for a part of or the whole structures on a broad space to examine the size of structures inevitably varied in the process of welding (assembly process). It leads to waste of time, space and human efforts, worry of safety accidents with the characteristic of the work to be performed on a high place, and non-efficiency and non-economy by using such supplementary equipments as crane. This paper, to remove the needless preassembly process by pre-estimating welding deformation produced under construction of large steel structures, devises a method modeling welded part for applying the equivalence load method and examines the effects of welding sequence and self weight on welding deformation by the method.

• Journal of Power System Engineering
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• v.20 no.3
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• pp.51-56
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• 2016

In this study, the tensile tests and hardness tests were carried out for the joints characteristics in friction stir welds of Al 5052 alloy. Three way factorial design was applied to optimal welding conditions, whose control factors were shoulder diameter, rotation speed and welding speed of tool. From the results of this study, the optimum condition for maximum yield strength was predicted as the shoulder diameter of 15 mm, welding speed of 500mm/min and rotating speed of 1000 rpm. And the presumed optimal yield strength was estimated to be $167.36{\pm}7.82MPa$ with 99% reliability. In addition the increaser rotation speed of tool and the decreaser welding speed, the decreaser the hardness at welding part.

• Journal of Welding and Joining
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• v.32 no.5
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• pp.1-6
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• 2014

This study aims at manufacturing SA welded API-X70 line-pipe with sour gas resistance. A pipe was manufactured by JCO bending process and SA welding using the API-X70 plate guaranteed HIC resistance. SA welded pipe was expanded in order to reduce the residual stress. The evaluation of a pipe for resistance to HIC and SSCC were performed by the RS D 0004 and RS D 0005 standards. For verification that a pipe has acceptable resistance to HIC, fullscale test was carried out. Results showed no cracking for the HIC and SSCC.