• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.148-159
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• 1998

Spot welding palys a key role in increasing productivity and weight reduction of the final products. This paper proposes a systematic approach on the design of spot weld configuration, dealing with the requried number and location of spot weld joints under the given design parameters, such as the applied loads, lap area, and individual spot weld strength. The optimal design of a spot-welded joint is postulated as a state when the safety factors of all spot weld points (i) are evenly distributed and (ii) reach maximum value. A CAD program is developed to arrange the optimal location of each spot weld based on the derived objective function and constraints. The CAD tool integrates the optimization procedure with Finite Element Analysis (FEA) code through an interface. The interface automatically provides geometrical data and mesh configuration for different spot weld locations to FEA model. It also extracts the transmitted load of each spot weld from the FEA code, and allows the optimization code predict an improved arrangement of spot weld locations. The feasibility of the developed approach is demonstrated by the selected examples.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.348-352
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• 2004

In finite element analysis of mechanical behavior of weld, typical process is first to obtain a finite element model containing residual stress by conducting welding analysis and then to examine the computational specimen for various external loading. The numerical specimen with residual stress has irregular boundary lines since one usually begins the welding analysis from a body having regular straight boundary lines and large thermal contraction takes place during cooling of weld metal. We notice that these numerical weld specimens are different from the real weld specimens as the real specimens are usually cut from a bigger weld part and consequently have straight boundaries neglecting elastic relaxation associated with the cutting. In this paper, an iterative finite element method is described to obtain a weld specimen which is bounded by straight lines. The stress distributions of two types of weld specimen, one with regular and the other with irregular boundaries, are compared to check the effect of the boundary shape. Results show that the stress distribution can be different when large plastic deformation is induced by the application of external loading. In case of elastic small deformation, the difference turns out almost negligible.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.550-555
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• 1993

The aim of this paper is to present the development of visual seam tracking system equipped with visual range finder. The visual range finder, which consists of a CCD camera and a diode laser system with line generating optics, developed to recognize the types of weld joints and detect the location of weld joints. In practical applications, however, images of the weld joints are often degraded due to spatters, are flares, surface specularity, and welding smoke. To overcome the problem, this paper proposes a syntactic approach which is a class of artificial intelligence techniques. In the approach, the type of weld joint is inferred based upon the production rules which are linguiques grammars consisting of a set of line and junction primitives of laser strip image projected on weld joint. The production rules eliminate several noisy primitives to create new primitives through the merging process of primitives. After the recognition of weld joint, arc welding is started and the location of weld joints is repeatedly detected using a spring model-based template matching in which the template model is a by-product of the recognition process of weld joint. To show the effectiveness of the proposed approach a series of experiments-identification and robotic tracking-are conducted for four different types of weld joints.

• Journal of Welding and Joining
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• v.24 no.5
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• pp.29-36
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• 2006

In this study, an experimental method for the selection of optimal welding condition was proposed in the fillet weld which was done over the tack weld. This method used the response surface analysis in which the leg length and the reinforcement height were chosen as the quality variables of the weld bead profile. The overall desirability function, which was combined desirability function fur the two quality variables, was employed as the objective function for getting the optimal welding condition. In the experiments, the target values of the leg length and the reinforcement height are 6m and zero respectively for the horizontal fillet weld of 10mm thickness mild steel. The optimal welding conditions could predict the weld bead profile(leg length and reinforcement height) as 6.00mm and 0.19mm without tack weld and 6.00mm and 0.48mm with tack weld. from a series of welding test, it was revealed that a uniform weld bead can be obtained by adopting the optimal welding condition which was determined according to the method proposed.

• Journal of Korean Society of Steel Construction
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• v.11 no.1 s.38
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• pp.1-11
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• 1999

The aim of this study is to construct a machine vision monitoring system for an automatic visual inspection of weld joint in steel structure. An image processing algorithm for a visual weld defects detection on weld bead is developed using the intensity image. An optic system for getting four intensity images was set as a fixed camera position and four different illumination directions. The input images were thresholded and segmented after a suitable preprocessing and the features of each region were defined and calculated. The features were used in the detection and the classification of the visual weld defects. It is confirmed that the developed algorithm can detect weld defects that could not be detected by previously developed techniques. The recognized results were evaluated and compared to expert inspectors' results.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.76-81
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• 2002

The dramatic increase in the depth of a weld bead penetration has been demonstrated by welding a stainless steel in GTA (Gas-Tungsten-Arc) process with activating flux which consists of oxides and halides. However, there is no commonly agreed mechanism fer the effect of flux on the process. In order to make clear the mechanism, each behavior of the arc md the weld pool in GTA process with activating flux is observed in comparison with a conventional GTA process. A constricted anode root is shown in GTA process with the activating flux, whereas a diffuse anode root is shown in the conventional process. These anode roots are related strongly to metal vapor from the weld pool and the metal vapor is also related to temperature distributions on the weld pool surface. Furthermore, it is suggested that a balance between the Marangoni force and the drag force of the cathode jet should dominate the direction of re-circulatory flow in the weld pool. The electromagnetic force encourages the inward re-circulatory flow due to the constricted anode root in the case with flux. The difference in flow direction in the weld pool changes the geometry or depth/width ratio of weld bead penetration.

• Journal of Welding and Joining
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• v.18 no.3
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• pp.60-67
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• 2000

In this study, we constructed a preview-sensing visual sensor system for weld seam tracking in GMA welding. The visual sensor consists of a CCD camera, a diode laser system with a cylindrical lens and a band-pass-filter to overcome the degrading of image due to spatters and/or arc light. To obtain weld joint position and edge points accurately from the captured image, we compared Hough transform method with central difference method. As a result, we present Hough transform method can more accurately extract the points and it can be applied to real time weld seam tracking. Image processing is carried out to extract straight lines that express laser stripe. After extracting the lines, weld joint position and edge points is determined by intersecting points of the lines. Although a spatter trace is in the image, it is possible to recognize the position of weld joint. Weld seam tracking was precisely implemented with adopting Hough transform method, and it is possible to track the weld seam in the case of offset angle is in the region of $\pm15^{\circ}$.

• Journal of Welding and Joining
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• v.34 no.5
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• pp.47-53
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• 2016

The aim of this study is to consider effect of weld elastic modulus on simulations of stress concentration and fatigue life for pressure vessel. The investigations include analysis with ADINA and WINLIFE softwares for whole body model about using condition of the boiler vessel. Values of weld elastic modulus were divided by 5 steps in butt weld area of the boiler vessel body. The stress concentration of the butt weld more was increased in case of higher elastic modulus of weld area because of higher difference of material properties between matrix and weld. It was concluded that the fatigue lives were decreased along increasing stress concentration due to high elastic modulus of weld. The matrix microstructure was estimated as pearlitic structure of ${\alpha}$ ferrite and pearlite. And the microstructures of welds along 5 steps of elastic modulus were estimated as bainitic fine pearlite and martensite as increasing elastic modulus.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1997.10a
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• pp.189-193
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• 1997

Generally, though we use the vision sensor or arc sensor in welding process, it is difficult to define the welding parameters which can be applied to the weld quality control. Especially, the important parameters is Arc Voltage, Welding Current, Welding Speed in arc welding process and they affect the decision of weld bead shape, the stability of welding process and the decision of weld quality. Therefore, it is difficult to determine the unique relationship between the weld bead geometry and the combination of various welding condition. Due to the various difficulties as mentioned, we intend to use Fuzzy Logic and Neural Network to solve these problems. Therefore, the combination of Fuzzy Logic and Neural network has an effect on removing the weld defects, improving the weld quality and turning the desired weld bead shape. Finally, this system can be used under what kind of welding process adequately and help us make an estimate of the weld bead shape and remove the weld defects.

• International Journal of Korean Welding Society
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• v.1 no.2
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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.