• Journal of Welding and Joining
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• v.29 no.5
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• pp.1-3
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• 2011

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.130-132
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• 2006

In passenger ship building where thin plates are mainly used, conventional arc welding processes result in significant post-weld reworking due to thermal distortion of welded joints. In order to solve this problem, European shipbuilding industries introduced hybrid welding process since the 1990's. for passenger ship, first of all, stability is very important. So, in this study, we investigated effects of hybrid welding conditions on impact toughness of weld metal in passenger ship building using DH36 steel.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.280-282
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• 2006

Prediction and control of the thermal distortion is particularly important for the design and manufacture of welded thin plate panel. In this study, experiments and computations are peformed to analyze how hole configuration and the size of the specimen effect on distortion. In addition, this study aims to develop a thermal elasto-plastic simulation using finite element method to predict distortion, with particular emphasis on buckling deformation generated in attachments welded around hole.

• International Journal of Ocean System Engineering
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• v.3 no.2
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• pp.95-101
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• 2013

This study is mainly interested in roundness of a circular moonpool structure in FPSO. Because this structure needs abrasion-resistance on inner wall, we should do buttering widely and deeply by using Inconel. But a general buttering can cause a severe distortion at structures. If someone can analyze the roundness by thermal distortion under Inconel over-lay, an erection policy can be established. In this study, shrinkage methodology by designed stress-strain curve was used and the result allowed deciding an appropriate block size.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.93-100
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• 2008

There are two ways of conventional thermal distortion analysis. One is the thermal elasto-plastic analysis and the other is the equivalent forces method based on inherent strain. The former needs exorbitant analysis time, while the latter cannot obtain results of stress field and it needs much time consumption with loads modeling on curved plates. Such faults in two methods have made difficulties in thermal distortion analysis of a large structure like ship hull. In order to solve them, new kind of thermal distortion analysis method was developed. We devised that the inherent strains was used as direct input factors in forms of boundary conditions. It was embodied by using thermal expansion coefficient in commercial code. We used the pre-calculated inherent strain as thermal expansion coefficient, and endowed nodes with imaginary temperatures. This method was already adopted at hull block welding distortion analysis which was considered as impossible, and gave productive results such as reduction of work time in the dry dock.

• Proceedings of the KWS Conference
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• 2000.10a
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• pp.166-169
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• 2000

This paper presents a study on the LD Pump laser welded heat transfer and distortion analysis by using finite element method. In the production processing, ferrule and saddle of LD Pump in light-wave communication system are welded by multi mode Nd-YAG laser. Thus distortion happens during laser-welded packaging, and it makes an error of detecting the light signal translated through optical fiber in LD Pump. These parts experience thermal and mechanical hysteresis during heating and cooling process come from laser welding. The amount of final displacement is predicted using the finite element method. And the optimal shape is decided by using the result of pre-analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.390-398
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• 2001

Welding process generates distortion and residual stress in the weldment due to rapid heating and cooling. Welding distortion and residual stress in the welded structure result in many troubles such as dimensional inaccuracies in assembling and safety problem during service. The accurate prediction of welding residual stress is thus very important to improve the quality of weldment and find the way to reduce itself. This paper suggests new analysis method to predict welding residual stress by considering solid phase transformation during welding process. Using the method, analysis is performed for medium and low carbon steel. The analysis result for medium carbon steel reveals that case considering phase transformation has compressive residual stress in contrast with the case neglecting phase transformation because of martensite formation. However, for the case of low carbon steel, residual stress shows little difference between the case considering phase transformation and the other case, because it has small transformation strain and recovers rapidly stress after phase transformation.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.3
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• pp.41-49
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• 1997

Laser spot welding offers a unique combination of high speed. precision and low heat distortion, compared with conventional resistance spot welding. This combinatin of advantages is especially attractive for the automotive industry. Until now automobile fabrication is widely used resistance spot welding, however, because of geometric and structural problem, spot welding is required many welding machine in that reason by substituting spot welding with laser welding, it save the equipment cost. In the present study we measured ultimate strength and observed bead cross section of laser welded specimen and compared with that of the resistance spot welding results in order to adapt laser welding in automobile industry. Also for strength esti- mation we calculated the residual stress of laser welded zone. All calculations are performed with the ABAQUS code on a workstation.

• Journal of Welding and Joining
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• v.17 no.5
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• pp.55-60
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• 1999

In thin plate welding, welding deformation is deformation is produced in special form like buckling distortion, which is different from one in thick plate welding, large quantitatively, and has complicated form. Therefore, a particular countermeasure to prevent the welding deformation in manufacturing process is requested. Otherwise it takes more time to straighten the welding deformation than to fabricated a steel structure newly and in case of failing to straighten the welding deformation in beginning of the flame straightening process, even if the flame straitening is completed, the appearances is not good and sometimes eve refabrication is needed. To minimize these problems. In this present paper, the effects of the condition of support pin on out-of plane deformation produced by thin plate Butt welding in investigated through experiment and the countermeasure to prevent the welding deformation in suggested.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.49-60
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• 2002

Welding is essential in ship production since welding is very popular method for joining two or more metals. However, welding causes residual stress and distortion and these give a bad influence to the structure strength and assembly of ship blocks. Therefore, prediction and treatment of residual stress and distortion is a key to accuracy control in shipyard. In this paper, a computational procedure, based on thermal-elastic-plastic 3-dimensional FEA, has been suggested to simulate butt and fillet welding process. In the simulation process, temperature distribution at each time step is obtained by heat transfer analysis and then thermal deformation analysis is done with obtained temperature distributions to find the residual stress and distortion. In heat transfer analysis, enthalpy method is used to realize phase change at melting temperature. Also element birth and death method is used to simulate adding of weld metal in both heat transfer analysis and thermal elastic plastic analysis. The proposed procedure is verified by related researches and the results show good agreement with those of related researches.