• Journal of Welding and Joining
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• 제21권1호
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• pp.60-65
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• 2003

At present. welding of most pipes with large diameter is carried out by the manual process. Automation of the welding process is necessary f3r the sake of consistent weld quality and improvement in productivity. In this study, two vision sensors, based on the optical triangulation, were used to obtain the information for seam tracking and detecting the weld defects. Through utilization of the vision sensors, noises were removed, images and 3D information obtained and positions of the feature points detected. The aforementioned process provided the seam and leg position data, calculated the magnitude of the gap, fillet area and leg length and judged the weld defects by ISO 5817. Noises in the images were removed by using the gradient values of the laser stripe's coordinates and various feature points were detected by using an algorithm based on the iterative polygon approximation method. Since the process time is very important, all the aforementioned processes should be conducted during welding.

• International Journal of Korean Welding Society
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• 제1권2호
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• pp.36-44
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• 2001

To get the appropriate welding process variables, mathematical modeling in conjunction with many experiments is necessary to predict the magnitude of weld bead shape. Even though the experimental results are reliable, it has a difficulty in accurately predicting welding process variables for the desired weld bead shape because of nonlinear and complex characteristics of welding processes. The welding condition determined for the desired weld bead shape may cause the weld defect if the welding current/voltage/speed combination is improperly selected. In this study, the $2^{n-1}$ fractional factorial design method and correlation parameter were used to investigate the effect of the welding process variables on the fillet joint shape, and the multiple non-linear regression analysis was used for modeling the gas metal arc welding(GMAW）parameters of the fillet joint. Finally, a fuzzy rule-based method and a neural network method were proposed so that the complexity and non-linearity of arc welding phenomena could be effectively overcome. The performance of the proposed neuro-fuzzy system was evaluated through various experiments. The experimental results showed that the proposed neuro-fuzzy system could effectively check the welding conditions as to whether or not weld defects would occur, and also adjust the welding conditions to avoid these weld defects.

• Journal of Welding and Joining
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• 제34권4호
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• pp.55-61
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• 2016

During laser overlap welding of galvanized steel sheets, explosion of weld pool by the high pressure zinc vapor induces weld defects like porosity and blowhole. In this study, laser 2-pass welding was implemented to prevent the weld defects. Through the 1st pass welding, zinc layers on the faying surfaces were removed when proper heat input was applied. Excessive heat input could result in explosion even during the 1st pass welding and insufficient heat input could not remove enough region of zinc layer for the 2nd pass welding. Coating weights of $45g/m^2$ and $60g/m^2$ were considered and for both cases sound welds without weld defects could be achieved. In spite of 2-pass welding, softening of weld and heat affected zone was not observed and Zn coating was not diluted into the weld metal.

• Journal of Electrical Engineering and Technology
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• 제7권6호
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• pp.1001-1008
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• 2012

Non-destructive testing (NDT) is a technique used in science and industry to evaluate the properties of a material without causing damage. In this paper we propose a method for segmenting radiographic images of welding in order to extract the welding defects which may occur during the welding process. We study different methods of level set and choose the model adapted to our application. The methods presented here take the property of local segmentation geodesic active contours and have the ability to change the topology automatically. The computation time is considerably reduced after taking into account a new level set function which eliminates the re-initialization procedure. Satisfactory results are obtained after applying this algorithm both on synthetic and real images.

• International Journal of Korean Welding Society
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• 제1권1호
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• pp.23-30
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• 2001

Among the various welding conditions, the welding current that is inversely proportional to the tip-to-work-piece distance is an essential parameter as to monitor the GMAW process and to implement the welding automation. Considering the weld pool surface geometry including weld defects, it should modify the signal processing method for automatic seam tracking in horizontal fillet welding. To meet the above necessities, a mathematical model related with the weld pool geometry was proposed as in a conjunction with the two-dimensional heat flow analysis of the horizontal fillet welding. The signal processing method based on the artificial neural network (Adaptive Resonance Theory) was proposed for discriminating the sound weld pool surface from that with the weld defects. The reliability of the numerical model and the signal processing method proposed were evaluated through the experiments of which showed that they are effective for predicting the weld bead shape with or without the weld defects in a horizontal fillet welding.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1309-1319
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• 1996

The research for the classification of the natural defects in welding zone is performd using the neuro-pattern recognition technology. The signal pattern recognition package including the user's defined function is developed to perform the digital signal processing, feature extraction, feature selection and classifier selection, The neural network classifier and the statistical classifiers such as the linear discriminant function classifier and the empirical Bayesian calssifier are compared and discussed. The neuro-pattern recognition technique is applied to the classificaiton of such natural defects as root crack, incomplete penetration, lack of fusion, slag inclusion, porosity, etc. If appropriately learned, the neural network classifier is concluded to be better than the statistical classifiers in the classification of the natural welding defects.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.370-376
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• 2005

Magnesium alloys are becoming important material for light weight car body, due to their low specific density but high specific strength. However they have a poor weldability, caused high oxidization tendency and low vapor temperature. In this study, the welding performance of magnesium alloys was investigated for automobile application. The materials were rolled magnesium alloy sheet contains Al and Zn such as AZ3l , AZ6l and AZ9l. Three types of welding process were studied, that were GTAW, Laser beam welding and FSW. To evaluate the weldability, we examined the appearance of welding bead. Also we checked bead shape and internal defects such as crack and porosity on cross section of welding bead. The mechanical property was measured for welded specimen by tensile test. For determination of the strength change by welding process, the hardness profile across the welding center was measured. For the results, the tensile properties of welded specimen were decreased obviously on all welding process. For the fusion welding process such as GTAW and laser beam welding, the surface of the welding bead was covered with oxidized magnesium dust but it was removed by simple cleaning work as wipe-out with tissue. Also under cut, that caused vaporization of base metal was occurred. for the friction stir welding, there was no oxidation, under-cut or internal defects. However it had poor weld performance, the reason was cleavage fracture occurred at plastic deformation zone. For welding of magnesium alloy, the laser beam welding process was recommended.

• Journal of Welding and Joining
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• 제29권3호
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• pp.82-88
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• 2011

With a tendency for the application of thin magnesium alloy plates in portable electronic equipment such as cell phone and notebook PC, there is a requirement to develop a welding technology for the lap welding of these thin magnesium alloy. This paper presents the single pulsed laser welding of AZ31B magnesium alloy. The effects of fiber types and parameters such as peak power and pulse width on laser weldability were investigated. The results show that weld defects, especially solidification crack, were always generated in the weld. These defects couldn't be controlled by the simple square pulse, but could be improved through the application of variable pulse. It is because that variable pulse has effect of solidification delay by dropping peak power gradually.

• Journal of Welding and Joining
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• 제33권4호
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• pp.63-67
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• 2015

Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing(ECT) is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. The New ECT sensor which can detect inner defects was developed regardless the condition of surface. This sensor is verified to do experiment which measure the loss of induced electromotive force. The loss of induced electromotive force was measured in 5.4% and this low frequency ECT device can detect internal defects at depth 20 mm.

• 한국정밀공학회지
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• 제27권1호
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• pp.99-104
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• 2010

Magnesium and magnesium alloys, the lightest structural materials, have been received plenty of global attention recently. These alloys could be applied in various fields, especially the electronics industry, because of their excellent electromagnetic interference shielding. However, the welding technique of magnesium alloys has not been established. This study is related to the welding of AZ31B magnesium alloy by a short-pulsed a Nd:YAG laser. Two types of pulse waves, square pulse and variable pulse, were used to control weld defects. Results show that the crack and porosity, generated in the weld, had not been controlled by general square pulse. But through the application of variable pulse, the defects could be prevented and the good weld zone was obtained.