우주 환경에서 GHTAW 아크 특성과 용융지 해석에 관한 연구

이상훈,나석주,Lee, Sang-Hoon,Na, Suck-Joo 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.4

The purpose of this paper is to understand the behavior of GHTAW process under the space environment with the experimental and numerical analysis. Gas Hollow Tungsten Arc Welding (GHTAW) using a hollow tungsten electrode was adopted, since the ignition and discharge of a conventional GTAW process is not appropriate to the space environment due to low pressure in space. In order to clarify the phenomena of GHTAW under space environment, an investigation of thermal and physical properties of the GHTAW arc plasma was experimentally performed under low pressure conditions. Furthermore, the molten pool behavior and weldment of GHTAW were understood by CFD-based numerical analysis, based on the models of GHTA heat source, arc pressure and electromagnetic force induced by arc plasma, the characteristics of which were obtained by the captured images of a CCD camera.

펄스형 Nd:YAG 레이저와 단락이행모드의 직류 GMA 열원을 이용한 하이브리드 용접 공정에 대한 연구

조원익,나석주,Cho, Won-Ik,Na, Suck-Joo 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.6

Until now, many researches on laser-arc hybrid welding processes have been conducted mainly for high power CW laser and high direct current arc to weld the thick steel plates for shipbuilding. Recently, however the usage of thin steel plates, which tend to be deformed easily by thermal energy, is been increasing because of demand of light structure such as car body in the automobile industry. Accordingly, heat sources having relatively low heat input such as pulsed laser, dip-transfer DC GMA and pulsed GMA seem to be applied more increasingly and the study about those heat sources is needed more intensively. Any heat source mentioned above can not stand alone without weld defects at a relatively high welding speed for increasing the welding productivity. This is main reason to apply the hybrid welding process which uses pulsed laser and low-heat-input GMA heat sources simultaneously to weld the thin steel plate. In this study, parameters of pulsed laser and dip-transfer DC GMA welding are studied firstly through preliminary experiments, and then analyzed in the viewpoint of their physical phenomena. Before conducting the hybrid welding, a pulse control technique is developed based on the parallel port communication and Visual C++ 6.0. Owing to development of this technique, interactions of laser and arc pulses can be controlled consistently. Using the pulse control technique, the hybrid welding is conducted and then its interactive welding phenomenon is analyzed.

FCA 필릿 파이프 용접에서 다중 비선형 회귀 모형과 구간적 3차 에르미트 보간법을 통한 비드 형상 예측

조대원,나석주,이목영,Cho, Dae-Won,Na, Suck-Joo,Lee, Mok-Young 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.5

Pipe welding is used in various ranges such as civil engineering and ship building engineering. Until now, many technicians work for pipe welding manually under harmful, dangerous and difficult conditions. So it is necessary to install automation process. For automation pipe welding, relation between welding parameters & bead shape should be considered. Using this relation, bead shape could be expected from welding parameters. FCAW was used in this study. Instead of pipe workpiece, fillet joint plate is used, which were inclined 0,45,90,135,180 degree. By analyzing between welding parameters (current, welding speed, voltage) and bead shape parameters with non-linear multiple regression, bead shape parameters could be expected. Piecewise Cubic Hermite Interpolation was used to expect smooth curved bead shape with bead shape parameters. From these processes, bead shape could be expected from welding parameters.

용접자동화를 위한 주사빔을 이용한 시각센서에 관한 연구

유원상,나석주,You, Won-Sang,Na, Suck-Joo 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.3

The vision sensor which is based on the optical triangulation theory with the laser as an auxiliary light source can detect not only the seam position but the shape of seam. In this study, a vision sensor using the scanning laser beam was investigated. To design the vision sensor which considers the reflectivity of the sensing object and satisfies the desired resolution and measuring range, the equation of the focused laser beam which has a Gaussian irradiance profile was firstly formulated, Secondly, the image formaing sequence, and thirdly the relation between the displacement in the measuring surface and the displacement in the camera plane was formulated. Therefore, the focused beam diameter in the measuring range could be determined and the influence of the relative location between the laser and camera plane could be estimated. The measuring range and the resolution of the vision sensor which was based on the Scheimpflug's condition could also be calculated. From the results mentioned above a vision sensor was developed, and an adequate calibration technique was proposed. The image processing algorithm which and recognize the center of joint and its shape informaitons was investigated. Using the developed vision sensor and image processing algorithm, the shape informations was investigated. Using the developed vision sensor and image processing algorithm, the shape informations of the vee-, butt- and lap joint were extracted.

작은 그루브 각을 가지는 맞대기 P-GMA 용접에서의 용접전류에 관한 연구

김륜한,나석주,김철희,Kim, Ryoon-Han,Na, Suck-Joo,Kim, Cheol-Hee 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.4

The purpose of this paper is to propose a mathematical model of welding current for the P-GMAW by modifying the well known GMAW model. Welding power circuit is simply modeled as a RL electric circuit and solved as an ODE equation. The welding current depends on the joint shape, molten pool and welding parameters. To compare the molten pool effect to the welding current, CFD numerical simulation technique was adopted. Welding experiment is also conducted with the same welding parameters as used in numerical simulations to verify the proposed welding current model. The current model which is considered molten pool shape, is more fit to experiment result.

금속 샌드위치 판재 대면적 롤 프로젝션 용접에 관한 연구 : Part 2 - 수치 해석

김종화,안준수,나석주,Kim, Jong-Hwa,Ahn, Jun-Su,Na, Suck-Joo 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.3

Metallic sandwich plate has many good properties such as high specific stiffness, high specific strength, good impact absorptivity, effective thermal insulation and soundproofing. In our study, a new bonding method, 3-layer roll projection welding, is introduced to fabricate the metallic sandwich plate. The new method uses a pair of roll electrodes like the seam welding, and projection welding is made at two internal interfaces of the 3-layer weldment consisting of a structured inner sheet and a pair of skin sheets. During the welding process, skin sheet temperature are measured to produce metallic sandwich plate with uniform and good quality. But it is difficult to observe or measure the temperature at the welding points during welding process because the welding points exist at the internal interfaces. Therefore FEM numerical analysis using ABAQUS is conducted to estimate the generated heat at the welding points with different welding conditions.

저항 용접을 이용한 금속 샌드위치 판재 접합에 관한 연구 : Part 2 - 공정해석

이상민,김진범,나석주,Lee Sang-Min,Kim Jin-Beom,Na Suck-Joo 대한용접접합학회 2005 대한용접·접합학회지 Vol.23 No.6

In part 1. optimal process parameters such as thickness of stopper and welding time are achieved to produce high strength ISB(Inner Structured and Bonded) panels. Developed process is different from the usual resistance welding process in the number of points welded at a time. In part 2, Numerical modeling for this new process is proposed and the variation of contact area with respect to the gap of electrodes is studied through FE analyses, Besides, it is tried to figure out the welding nugget formation and proper distance between welding points. FE analytic results show that inner structures are melted more than skin plate, and current distribution between points to be welded can be controlled by distance welding points. Comparison of some FE analytic results with corresponding experimental results could confirm the validity of the proposed numerical modeling.

금속 샌드위치 판재 대면적 롤 프로젝션 용접에 관한 연구 : Part 1 - 공정 모니터링

안준수,김종화,나석주,임지호,Ahn, Jun-Su,Kim, Jong-Hwa,Na, Suck-Joo,Lim, Ji-Ho 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.3

A roll projection welding machine is introduced to fabricate metallic sandwich plate consisting of a structured inner sheet with projection-like shape and a pair of skin sheets. To fabricate the metallic sandwich plate of consistent and good quality, two process monitoring methods are introduced; dynamic resistance monitoring and skin sheet temperature monitoring. Dynamic resistance monitoring has no time delay but gives only averaged value over plate width. Skin sheet temperature monitoring has certain amount of time delay but is good for predicting weld quality of specified position. By the two complementary monitoring methods, the characteristics of the new welding process is successfully understood.

Nd:YAG 레이저를 이용한 폴리머의 투과접합에서 열 유동 및 열 변형 해석

차상우,김진범,나석주,Cha, Sang-Woo,Kim, Jin-Beom,Na, Suck-Joo 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.6

Laser Transmission Joining (LTJ), which is a joining process of polymers by using different transmission rates of materials, was studied numerically. Unlike previous studies, energy loss by reflection at the surface was included. Besides, energy absorbed in the transparent substrate is also considered to increase the accuracy of the analytical results. Furthermore, thermal deformations of the substrates were also calculated. Temperature distribution of the substrates on the joining process could be effectively predicted by using the thermal analysis model developed, which could also analyze the rising phenomenon of the absorbing substrate by bulge effect. Calculated results show that temperature of the absorbing substrate is higher than that of transparent substrate when the laser is being radiated, and this temperature difference causes more thermal deformation in absorbing substrate, which results in the surface rise of the absorbing substrate. Comparison of calculated results with corresponding experimental results could confirm the validity of the numerical analysis model proposed.

위상이동 ESPI를 이용한 미세용접변형 측정에 관한 연구

이건하,김지태,나석주,Lee, Gun-Ha,Kim, Ji-Tae,Na, Suck-Joo 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.12

ESPI is a noncontact, nondestructive and relatively fast inspection method. For these reasons ESPI is being applied as a valuable tool in the nondestructive evaluation of structural components. Phase shifting ESPI is used more effectively than the traditional ESPI because spatial resolution of small object displacements are improved and numerical phase values are obtained for all pixels in the image. Consequently the quantitative measurement of deformation is possible. ESPI fringe patterns are contaminated with high levels of speckle noise. Therefore the phase image is to be smoothed to remove the noise and obtain a better signal-to-noise ratio. In this study, smoothing is done by phase shifting convolution to avoid smoothing errors close to the 2$\pi$ phase ambiguities in the deformation phase image, and median filter is used as a smoothing filter.