• Journal of Welding and Joining
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• v.13 no.4
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• pp.155-162
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• 1995

Redistribution of residual stress and its effects during fatigue crack propagates from tensile residual stress region in weldment are investigated. Tests are performed by using welded CCT specimens of structual rolling steel (SS400) and it makes fatigue crack propagate from tensile residual stress region. For this study tension-tension loading type is selected by external loading condition and magnetizing stress indicator is used correctly to measure redistribution of residual stress according to fatigue crack growth and number of loading cycles. From this result, it is proved that redistribution of residual stress is mainly consist of residual stress released by fatigue crack growth. When fatigue crack propagates from tensile residual stress region residual stress are redistributed and it makes fatigue crack growth rate largely increase. Fatigue crack growth rate is low in case of redistributed residual stress compare with initial distributed residual stress.

• Journal of Welding and Joining
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• v.19 no.6
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• pp.600-607
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• 2001

A CCD camera with a laser stripe was applied to realize the automatic weld seam tracking in GMAW. It takes relatively long time to process image on-line control using the basic Hough transformation, but it has a tendency of robustness over the noises such as spatter and arc light. For this reason. it was complemented with adaptive Hough transformation to have an on-line processing ability for scanning specific weld points. The adaptive Hough transformation was used to extract laser stripes and to obtain specific weld points. The 3-dimensional information obtained from the vision system made it possible to generate the weld torch path and to obtain the information such as width and depth of weld line. We controled the wire feeding rate using informations of weld line.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.22-28
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• 2014

To enhance productivity and provide high quality production material in a GMA welding process, weld quality, productivity and cost reduction affects the number of process variables. In addition, a reliable welding process and conditions must be implemented to reduce weld structure failure. In various industries the welding process mathematical model is not fully formulated for the process parameter and on the welding conditions, therefore only partial variables can be predicted. The research investigates the interaction between the welding parameters (welding speed, distance between electrodes, and flow rate of shielding gas) and bead geometry for predicting the weld bead geometry (bead width, bead height). Taguchi techniques are applied to bead shape to develope curve equation for predicting the optimized process parameters and quality characteristics by analyzing the S/N ratio. The experimental results and measured error is within the range of 10% presenting satisfactory accuracy. The curve equation was developed in such a way that you can predict the bead geometry of constructed machinery that can be used for making tandem welding process.

• Journal of Welding and Joining
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• v.24 no.6
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• pp.39-43
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• 2006

A ferritic stainless steel, STS430, and a galvanized steel for case and frame of electronic goods are welded by resistance spot welding and resistance projection welding methods. In this study, resistance spot welding has been performed to investigate the weldability of dissimilar materials such as a ferritic stainless steel and a galvanized steel. Tensile load of the spot weld without heat treatment was 196 kN and brittle fracture occurred at interface between STS430 and nugget due to the high hardness, 380 Hv, in nugget. It was found that the hardness of as-welded nugget increased with higher cooling rate during resistance spot welding by comparing with GTA weld of same materials. Heat treatment by applying second current made nugget softened. Tensile load of heat treated weld increased and reached to 303 kN and fracture occurred at base metal, a galvanized steel.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.23-31
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• 2015

Stainless steel is used in automobile muffler and exhaust systems. However, in comparison with other steels it has a high thermal expansion rate and low thermal conductivity, and undergoes excessive thermal deformation after welding. To address this problem, we evaluated the use of arc brazing in place of welding for the processing of an exhaust system, and investigated the parameters that affect the joint characteristics. Muffler parts STS439 and hot-dipped Al coated steel were used as test specimens, and CuAl brazing wire was used as the filler metal for the cold metal transfer (CMT) welding machine, which is a low heat input arc welder. In addition, a Box-Behnken design of experiment was used, which is a response surface methodology. The main process parameters (current, speed, and torch angle) were used to determine the appropriate welding quality and the mechanical properties of the brazing part was evaluated at the optimal welding condition. The optimal processing condition for arc brazing was 135A current, 51cm/min speed and $74^{\circ}$ torch angle. The process was applied to an actual exhaust system muffler and the prototype was validated by thermal fatigue, thermal shock, and endurance limit tests.

• Journal of Welding and Joining
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• v.30 no.2
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• pp.54-58
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• 2012

Al-coated steel sheets with excellent heat and corrosion resistance are widely used in various applications. In welding of thin plate, some defects such as unmelted zone and metal-through occur easily in the beginning and ending of welding line. In the study, the welding defects in Al-coated steel sheets were investigated with respect to plasma arc current, height between Cu block and base metals, and using a roller to align the height of the base metal. Full penetration and voids free welds were obtained with a plasma arc current 52A and weld speed 2.3m/min. An unmelted zone increased and Ericshen rate decreased as the height between Cu block and base metal increased from 0 to 0.6mm. Using a roller moving ahead of the plasma arc, the length of unmelted zone decreased from 1.7mm to 0.5mm.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1322-1327
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• 2007

Many automotive companies have tried to apply the aluminum alloy sheet to car body because reducing the car weight can improve the fuel efficiency of vehicle. In order to do that, sheet materials require of weldablity, formability, productivity and so on. Aluminum alloy was not easy to join these metals due to its material properties. Thus, the laser is good heat source for aluminum alloy welding because of its high heat intensity. However, the welding quality was not good by porosity, underfill, and magnesium loss in welded metal for AA5182 aluminum alloy. In this study, Nd:YAG laser welding of AA 5182 with filler wire AA 5356 was carried out to overcome this problem. The weldability of AA5182 laser welding with AA5356 filler wire was investigated in terms of tensile strength and Erichsen ratio. For full penetration, mechanical properties were improved by filler wire. In order to optimize the process parameters, model to estimate tensile strength by artificial neural network was developed and fitness function was defined in consideration of weldability and productivity. Genetic algorithm was used to search the optimal point of laser power, welding speed, and wire feed rate.

• Laser Solutions
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• v.7 no.3
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• pp.11-24
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• 2004

In automotive industry, light weight vehicle is one of issues because of the air pollution and the protection of environment. Therefore, automotive manufacturers have tried to apply light materials such as aluminum to car body. Aluminum welding using laser has some advantages high energy density and high productivity. It is very important to understand behavior of plasma and keyhole in order to improve weld quality and monitor the weld state. In this study, spectral analysis was carried out to verify the spectrum for plasma which is generated in laser welding of A 6000 aluminum alloy. Two photodiodes which cover the range of plasma wavelength was used to measure light emission during laser welding according to assist gas flow rate and welding speed. Analysis of relationship between sensor signals of welding variables and formation of keyhole and plasma is performed. To determine the level of significance, analysis of variation (ANOVA) was carried out.

• Journal of Welding and Joining
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• v.25 no.2
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• pp.43-48
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• 2007

Laser Transmission Joining (LTJ) of plastics is a process in which light of suitable wavelength is transmitted through a transparent substrate that is in contact with an absorbing one. In this paper, LTJ is investigated by preliminary experiments from the viewpoint of mechanical engineering. To understand transmitting characteristics of each polymer substrate, transmission rate, reflection rate and absorption coefficient of polymer are measured by using a laser power-meter. Characteristics of joining in the spot welding and seam welding are investigated by measuring the fracture load. Fracture load increases in accordance to the laser power and irradiation time. However, when the laser power is over 60W and irradiation time over 4seconds, fracture load decreases. This phenomenon is probably due to heat-softening of materials. Besides, cavities are generated at a joint by evaporation of water molecules, which can be suppressed by introduction of a gap between two substrates.

• Journal of Welding and Joining
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• v.22 no.2
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• pp.59-68
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• 2004

Plasma transferred arc welding (PTAW) has been taken into consideration for repairing Ni-based superalloy components used gas turbine blades. Various cracks has been generally reported to be found in the base metal heat affected zone(HAZ) along grain boundary. Thus, hot cracking susceptibility of Ni-based superalloys was evaluated according to heat treatments. Hot ductility test was conducted on specimens with solution treated at 112$0^{\circ}C$ for 2 hours and aging treated at 845$^{\circ}C$ for 24hours after solution treatment. The results of the hot ductility test appeared that solution treated specimens were the highest ductility recovery rate among three conditions. The loss of ductility at high temperature in Ni-based superalloy was mainly controlled by the degree of pain boundary wetting due to constitutional liquation of MC carbide precipitates. Meanwhile, the highest ductility recovery rate in solution-treated alloys seems to be lack of M23C6, which can be dissolved during heating and then result in the local enrichment of Cr in the vicinity of the grain boundary.