• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.17-19
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• 2007

The fatigue experiments of friction stir welded Al-6061-T6 alloy with and with out back bead were performed to investigate the variation in fatigue strength and life of the Joint. It was found that there were always existed flaws at the roots of friction stir welds for the normal welding parameters and clamping conditions. In order to overcome this root flaws, friction stir welds with optimum back bead has been developed. The test results with root flaws and with back bead were compared. The fatigue life of weld with root flaws was 5-10 times shorter than that of the friction stir weld with back bead.

• 한국레이저가공학회지
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• 제12권1호
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• pp.19-24
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• 2009

Because of its fast and precise welding performance, laser welding is becoming a new excellent welding method. However, the precise focusing and robust seam tracking are required to apply laser welding to the practical fields. In order to laser weld a type of T joint like a circular pipe on a square pipe, which could be met in the three dimensional structure such as an aluminum space frame, a visual sensor system was developed for automation of focusing and seam tracking. The developed sensor system consists of a digital CCD camera, a structured laser, and a vision processor. It is moved and positioned by a 2-axis motorized stage, which is attached to a 6 axis robot manipulator with a laser welding head. After stripe-type structured laser illuminates a target surface, images are captured through the digital CCD camera. From the image, seam error and defocusing error are calculated using image processing algorithms which includes efficient techniques handling continuously changed image patterns. These errors are corrected by the stage off-line during welding or teaching. Laser welding of a circular pipe on a square pipe was successful with the vision tracking system by reducing the path positioning and de focusing errors due to the robot teaching or a geometrical variation of specimens and jig holding.

• Journal of Welding and Joining
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• 제23권4호
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• pp.41-47
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• 2005

Generally, the use of robots in manufacturing industry has been increased during the past decade. GMA(Gas Metal Arc) welding process is an actively Vowing area, and many new procedures have been developed for use with high strength alloys. One of the basic requirement for the automatic welding applications is to investigate relationships between process parameters and bead geometry. The objective of this paper is to develop a new approach involving the use of neural network and multiple regression methods in the prediction of bead geometry for GMA welding process and to develop an intelligent system that visualize bead geometry in order to employ the robotic GMA welding processes. Examples of the simulation for GMA welding process are supplied to demonstrate and verify the proposed system developed using MATLAB. The developed system could be effectively implemented not oかy for estimating bead geometry, but also employed to monitor and control the bead geometry in real time.

• 한국해양공학회지
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• 제21권1호
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• pp.64-68
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• 2007

Recently, there has been considerable research in the field of application of Laser-Arc hybrid welding for superstructures, such as ship-structures, transport vehicles etc. However, the study on heat distribution and welding residual stress of hybrid weld by numerical simulation leaves much to be desired. Therefore, in this study, an optimized welding condition and numerical simulation for hybrid welding, using previous numerical analysis to calculate the heat source for hybrid welding, has been analyzed. For this purpose, fundamental welding phenomena of the hybrid process, using Laser and, is investigated. In order to calculate temperature and residual stress distribution in hybrid welds, a finite element heat source model is developed on the basis of experimental results and characteristics of temperature. Residual stress distribution in hybrid welds are understood from the result of simulation, and compared with the experimental values.

• 한국안전학회지
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• 제16권3호
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• pp.1-6
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• 2001

The study is to investigate the influence on the fatigue crack growth behaviors for the welded configuration in pressure vessel stiffener. In order to perform this goal, the automatic welded specimens were prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. In skip welding of pad-on-plate, continuous fillet welding and PWHT specimen, fatigue crack is generally initiated at the starting and end old toe zone, and ruptured at the starting old toe zone. The fatigue life of pad-on-plate of the continuous fillet welding specimen is larger than that of pad-on-plate skip fillet welding specimen about 85% under low load, about 20% under high load and less than that of two-pad continuous fillet welding specimen about 85%. In da/dN-$\Delta$K curve under low load, skip fillet welding specimen of pad-on-plate showed retardation on the initial crack, and the fatigue crack growth rate at the low region of $\Delta$K greater specimen E($3.8 {\times} 10^{-6}mm/cycle$). And the fatigue life of welding specimen was smaller than that of PWHT specimen.

• 한국군사과학기술학회지
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• 제10권3호
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• pp.5-15
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• 2007

A welding structures is generally composed of dissimilar steel materials in order to reduce weight cost, and has a gap to fill the welding agent. Also, heat flow analysis should be fulfilled for structure existing of gap to figure out residual stress which is generated after welding. Since mechanical properties of welding structure composed of dissimilar steel is more fragile than mechanical properties of welding structure consisted of same material, heat flow analysis verifying this should be fulfilled as well. Therefore, on this research, heat flow analysis about dissimilar steel weldment consisted of gap existing AISI304 and AISI630 is practiced so that it could be a basic data of research about mechanical properties of gap existing dissimilar steel welding part which is going to be studied later on. During heat flow analysis, heat input model which based on Gaussian profile and using volume heat flux was newly consisted and applied. In addition, for verifying of analysis on this research, gap existing dissimilar steel weldment which had gap of 0.25mm and was welded using Nd-YAG. The welding profile and temperature distribution for weldment during welding was compared to the result which was gotten through heat flow analysis. Both of those results corresponded each other.

• 한국해양공학회지
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• 제33권2호
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• pp.153-160
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• 2019

Welding often results in welding distortion during the assembly process. The welding distortion of thin-plate structures such as the living quarters of ships and offshore installations is a more significant problem than in the case of thick-plate structures. Pre-stressing/heating and fairing, which are additional works to mitigate and control welding distortion, are inevitable, and the construction planning is accordingly delayed. In order to prevent welding distortion and minimize the additional work during the assembly process, increasing the plate thickness and/or the number of stiffeners may be a simple solution, but it may give rise to problems related to cost and weight. In this study, the welding distortion control effect of the type of stiffeners on the door openings of various living quarter structures was investigated using an experimental method and a finite element method. The results showed the feasibility of mitigating and controlling the welding distortion, and the optimum selection of the type of stiffeners was confirmed.

• International Journal of Korean Welding Society
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• 제2권1호
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• pp.15-20
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• 2002

This paper describes the weldability and mechanical behavior of JIS S45C medium carbon steel (corresponding to KS SM45C and SAE 1045) for machine structures in CW Nd:YAG laser welding. In general, medium carbon steels have a limited application to the industrial fields in spite of good mechanical characteristics. This is due to welding difficulty because of the high carbon contents and impurities in this material. Therefore, in this study the laser weldability of medium carbon steel with adjusted contents of S and P has been investigated in order to extend the application to medium carbon steels. Several experiments and numerical simulations have been conducted to determine the characteristics of mechanical behavior in CW Nd:YAC laser welds. The results of the simulations concur with the experiment results. From the result of this study, the application possibility of CW Nd:YAG laser welding to medium carbon steel has been confirmed. Also, the appropriateness of mechanical behavior simulation has been verified to analyze and predict the welding phenomena.

• International Journal of Korean Welding Society
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• 제1권2호
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• pp.12-17
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• 2001

With the advance of the robotic welding process, procedure optimization that selects the welding procedure and predicts bead width that will be deposited is increased. A major concern involving procedure optimization should define a welding procedure that can be shown to be the best with respect to some standard and chosen combination of process parameters, which give an acceptable balance between production rate and the scope of defects for a given situation. This paper presents a new algorithm to establish a mathematical model f3r predicting bead width through a neural network and multiple regression methods, to understand relationships between process parameters and bead width, and to predict process parameters on bead width for GMA welding process. Using a series of robotic arc welding, additional multi-pass butt welds were carried out in order to verify the performance of the neural network estimator and multiple regression methods as well as to select the most suitable model. The results show that not only the proposed models can predict the bead width with reasonable accuracy and guarantee the uniform weld quality, but also a neural network model could be better than the empirical models.

• 한국정밀공학회지
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• 제29권1호
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• pp.87-95
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• 2012

In recent years, laser-arc hybrid welding has begun to be adopted for assembly welding of automotive bodies and parts, because the hybrid welding process can weld lapped steel sheets having a larger gap than is possible with laser welding. In this paper, to predict the twist deformation by the hybrid welding when brackets are welded in B pillar of a passenger car, the residual stress using CAE is analyzed and the deformation result of CAE is compared with the measured deformation. First of all, after modeling heat source as intended to be expressed with laser-arc hybrid welding method, heat source fitting is done with welding conditions and a section of welding part obtained through specimen test. In case of heat source functions, laser used conical source and arc used double ellipsoid source. Through the local model analysis, elements which are located in the center of the model are selected. The elements are called WME(Welding Macro Element). This WME is extruded in the welding lines and welding phenomenon of complex parts is accomplished. The deformation amount after hybrid welding is got through a simulation, the validity of simulation is verified by measuring the panel and comparing with the simulation result.