• Journal of Welding and Joining
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• 제27권4호
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• pp.67-72
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• 2009

In this paper, arc characteristics of V groove joints using pulsed GMA welding were found out. The bevel angles of $22.5^{\circ}$ and $30.0^{\circ}$ were chose to make the V groove configuration with the groove angles of $45^{\circ}$ and $60.0^{\circ}$, respectively. In the experiment, the arc current waveform measurement and the high speed photography were taken to investigate the arc characteristics for a single-beveled asymmetric workpiece. Consequently, the welding current was changed abnormally around the edge of groove. As the arc moved close to the groove face, the welding current was increased rapidly because the welding arc was affected by the inclined surface. Also the welding current waveforms were measured for the double-sided symmetric workpiece to verify the previous measurements for the single-beveled workpiece, and similar current waveforms were found.

• Journal of Welding and Joining
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• 제26권2호
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• pp.85-91
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• 2008

In general, the quality of a welding process tends to vary with depending on the work environment or external disturbances. Hence, in order to achieve the desirable quality of welding, we should have the optimal welding condition that is not significantly affected by these changes in the environment or external disturbances. In this study, we used a dual response surface method in consideration of both the mean output variables and the standard deviation in order to optimize the V-groove arc welding process. The input variables for GMA welding process with the dual response surface are welding voltage, welding current and welding speed. The output variables are the welding quality function using the shape factor of bead geometry. First, we performed welding experiment on the interested area according to the central composite design. From the results obtained, we derived the regression model on the mean and standard deviation between the input and output variables of the welding process and then obtained the dual response surface. Finally, using the grid search method, we obtained the input variables that minimize the object function which led to the optimal V-groove arc welding process.

• 한국정밀공학회지
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• 제32권2호
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• pp.167-172
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• 2015

In order to prevent crack in thick weld zones, the preheating process such as induction and gas torch heating needs to be applied. Among them induction heating is the most effective heat source because it has rare thermal effect and very rapid heating characteristics. In this paper, when the induction heating method is used to improve arc welding, the temperature distribution and magnetic field density of the welding zones are analyzed by simultaneously solving heat transfer and electromagnetic field equation. In particular, cone and flat type coils are designed and induction heating effects of each type are compared to identify heating characteristics on a V-groove weld joint. As a result, a cone shape coil is more efficient in the preheating process. When induction heating and arc welding system is designed for thick plate with V-groove weld joint, the results in this paper could be applied.

• Journal of Welding and Joining
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• 제32권1호
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• pp.87-92
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• 2014

Recently, use of thick Al 5083 plate has increased in production of LNG storage tank. In general, multi-pass welding has been used to achieve sufficient penetration in thick plate welding. High current welding which enables high deposition and deep penetration is preferred in thick plate welding because the increase of number of pass increases manufacturing cost and formation of weld defect. In this study, welding characteristics according to various Ar/He shielding gas composition was investigated in high current MIG welding. The bead-on-plate welding and V groove welding were conducted on Al 5083 alloy with a thickness of .25 mm. The effect of shielding gas composition on bead shape was evaluated and proper shielding gas composition was proposed. Also arc stability was examined under selected shielding gas composition. One side-one pass welding experiments were conducted for V groove specimen with a thickness of 25 mm. Mechanical properties and hardness profiles were measured for the V groove specimens.

• Journal of Welding and Joining
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• 제22권6호
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• pp.57-63
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• 2004

Fracture toughness is an important parameter in designing offshore structures to ensure resistance to fracture at various temperatures. In this study, a series of experiments is carried out to obtain fracture toughness values (CTOD) of API 2W Gr.50B, welded using FCAW(Flux Cored Arc Weld). In particular, a comparison of absorbed impact energy and CTOD values are made with respect to two different welding groove shapes; double-V-groove and double-bevel-groove. Charpy impact tests are performed for specimens sampled near the root gap, and CTOD tests are carried out for three point bending specimens having the notch at weld zone. While Charpy impact test result is determined to be a good qualitative measure of fracture toughness, no quantitative correspondence between impact absorbed energy and CTOD values was found. Based on the experiment, it is observed that double-V-groove welds give lower transition temperature than those of double-bevel-groove.

• Journal of Welding and Joining
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• 제30권6호
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• pp.120-125
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• 2012

Because ships and offshore structures have very large dimensions and complicated shapes, it is difficult to determine the deformation or internal stress in the structure by simple lab tests. Thus, a rigorous analysis by using the computer simulation technology is essential for obtaining their distortions by considering the entire production process characteristics. The rapid development of computer technology made it possible to analyze the heat transfer phenomena, deformation and phase transformation in the welded joint. For large shell structures, shell elements modeling contributed primarily to this development. But if a welding is done by multi-pass, shell elements whose thickness are unchangeable can hard to describe the local situation. Recently, it was researched how to introduce the imaginary temperature for V grooved multi-layer butt welding in strain-boundary method (a kind of shrinkage methodologies). In the present study, we formulated the imaginary temperature for the double bevel and double V groove by considering the thickness change of each pass through the bead and the thickness directions simultaneously and also demonstrated the feasibility of the formula by applying it to the thermal distortion analysis of the erection process of crane pedestal.

• Journal of Welding and Joining
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• 제23권4호
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• pp.48-52
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• 2005

To estimate welding deformation for large steel structures, either experiment result with small specimen or analysis result of FEM with small numerical model is used. Consequently, it is important to decide the welding length of specimen and numerical model not to have an effect on welding deformation for accurate estimation of whole welding deformation. This study experimentally clarifies the effect of welding length on angular distortion due to welding by varying welding length of specimens, but fixing width and thickness of specimens on V-groove butt welding, fillet welding and bead on plate welding. As a resell the critical welding length on fillet welding and on bead on plate welding is over 500mm and on V-groove butt welding is over 1,000mm.

• International Journal of Korean Welding Society
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• 제4권1호
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• pp.23-29
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• 2004

In weaving welding where a V groove exists, the heat input distribution is an important factor that determines the defectiveness of the bead shape, undercut and over-lap. In this study, the amount of heat input, which is determined by the welding current, voltage, speed and weaving conditions is calculated through mathematical development and numerical methods. Furthermore, the heat input distribution as a two- dimensional heat source was observed when applied to each groove.

• Journal of Welding and Joining
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• 제13권4호
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• pp.122-131
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• 1995

An automatic welding equipment for thick plates requires the capability of the seam tracking of the weld line which often includes misalignment of the workpiece and variation of groove width. In this study, an automatic welding equipment and control algorithms based on the arc sensor were proposed for the GMA welding of thick plates which had misalignment and gap variation. The developed system being constituted with 5 axis can be automatically controlled by computer and also automnatically set the welding conditions such as welding current, and voltage. The proposed algorithms for the seam tracking in multi-pass welding of the thick plates were constituted as follows : the detection of weaving-end point for findng the variation of groove width, the control of welding velocity for acquiring a constant thickness deposition of weld metal, and the calculation of groove width and height of an arbitrary pass in the multi-pass weld. As results of the application of the system, it was revealed that the system had a good capability in seam tracking and made an excellent weld quality in V groove butt joint.

• 한국정밀공학회지
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• 제18권1호
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• pp.162-170
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• 2001

In torch weaving in arc welding on V groove, the heat input distribution on groove surface is a main factor determining the bead shape and the weld quality with and without the weld defects such as undercut, overlap, etc. In this study, we calculate the heat input varying with the welding current, arc voltage, welding speed and the touch weaving condition using numerical method. And we investigate the heat input distribution on groove surface while applying the various grooves having 2 dimensional heat sources.