CFD based visualization of the finger shaped evolution in the gas metal arc welding process

Cheon, Jason,Kiran, Degala Venkata,Na, Suck-Joo Elsevier 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.97 No.-

<P><B>Abstract</B></P> <P>A CFD based numerical study of the gas metal arc welding process was used to visualize momentum flow in the produced fingertip shaped molten pool. Arc process models were employed with temperature-independent material properties in a phase, and measured process parameters. The results of the welding simulation were in good agreement with the etched cross-section microscopy and temperature history of the experimental results. Molten pool speed information was utilized to track momentum flow in the weld pool using color maps and streamline plots. As results, it was determined that the droplet impingement momentum first strikes the bottom of the molten pool and digs a deep fingertip penetration. Then, the droplet impingement momentum detours backward at a deep level and moves forward at a shallow level, and widens the molten pool width.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The CFD GMAW simulation results were in good agreement with experimental results. </LI> <LI> The droplet impingement momentum was tracked velocity information. </LI> <LI> Initially the droplet digs a deep fingertip penetration. </LI> <LI> Next, the droplet impingement momentum detours backward at a deep level. </LI> <LI> And it moves forward at a shallow level, and widens the molten pool width. </LI> </UL> </P>

A study on transient flow characteristic in friction stir welding with real-time interface tracking by direct surface calculation

Cheon, Jason,Yoon, Jin-Young,Kim, Cheolhee,Na, Suck-Joo Elsevier 2018 Journal of materials processing technology Vol.255 No.-

<P><B>Abstract</B></P> <P>A numerical analysis model of friction stir welding was suggested by the direct interface area calculation method aided for axisymmetrically and non-axisymmetrically shaped tools. A general moving object was used to represent the tool movement based on the commercial CFD software. The plunging and welding processes were performed in the Eulerian description. Based on energy conservation laws, the torque induced power input, interface friction heat, and plastic deformation heat were modeled and evaluated. The measured temperature and torque were compared with the calculated results. The results of the combined error mode showed the conditionally acceptable results. The proposed model could be used for the torque and temperature prediction with a relatively short calculation time.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Prediction of welding residual stress with real-time phase transformation by CFD thermal analysis

Cheon, Jason,Na, Suck-Joo Elsevier 2017 International journal of mechanical sciences Vol.131 No.-

<P><B>Abstract</B></P> <P>A new method of numerical thermal-metallurgical-mechanical analysis for the gas metal arc welding process is proposed. The latest thermal-metallurgical analysis method, using real-time temperature and phase fraction history was employed in this study. The thermal-metallurgical strain behavior of a wide temperature range of austenization is considered, using dilatometry information and temperature and phase fraction dependent mechanical properties. A simple volumetric strain balance was used to describe the effect of phase transformation in the mechanical analysis. Following validation of the thermal-metallurgical analysis, the stress distribution predicted by the thermal-metallurgical-mechanical analysis was compared with measured directional stresses. In the results, the phase transformed weldment did not always appear to be expanded when a wide range of austenization temperatures was considered in the heating process. Moreover, the thermal-metallurgical-mechanical analysis of the welding process identified stress concentration on the near welding line, and nonlinear deflection by the gradient of total volumetric strain, and phase dependent yield strength. However, the model for this study did not consider the mechanical history reset of the liquid state. Also, the limitation of the stress measurement method made it difficult to make a detailed comparison with the calculated results. The model change method to allow treatment of the liquid state, and a neutron diffraction method for complete validation, will be utilized in future work to overcome these limitations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new method of numerical thermal-metallurgical-mechanical analysis is proposed. </LI> <LI> A new thermal-metallurgical strain behavior of welding process is proposed. </LI> <LI> A simple volumetric strain balance was used to describe the strain history. </LI> <LI> The phase transformed weldment is apparently not always expanded. </LI> <LI> The stress concentration was affected due to the phase dependent strain and yield strength. </LI> </UL> </P> <P><B>Graphic abstract</B></P> <P>[DISPLAY OMISSION]</P>

Interference fit process development for the ITER Vacuum Vessel Gravity Support mock-up fabrication

Cheon, Jason,Park, Chulkyu,Moon, Hokyu,Chung, Woo-Ho,Kim, Hyun-Soo,Hong, Kwen-Hee,Kim, Gwang-Ho,Kim, Yu-Gyeong Elsevier 2019 Fusion engineering and design Vol.146 No.2

<P><B>Abstract</B></P> <P>The ITER Vacuum Vessel (VV) is supported by the nine VV gravity supports (VVGS) located on the cryostat toroidal pedestal. The VVGS is dual hinge type that fastened by dowel in the hinge-block hole. This paper presents the technical approach and result on the interference fitting process of the sleeve to the full-scaled VVGS mock-up. Since the sleeve and the hinge-block hole have under millimeter tolerance and around two-meter long length, the shrink fit method has been selected for the interference fitting of the sleeve into the hinge-block hole. The duration time for required shrinkage was expected by the simple analytical approach of natural convective heat transfer. The coolant charging method was suggested to secure a sufficient time for the process. The liquid nitrogen was charged to the handling fixture capped sleeve hole’s cavity. As a result, the necessary contraction time was secured as thousands of seconds. Consequently, the interference fitting was successfully done for VVGS mock-up fabrication, and the technical solutions will be applied to the VVGS manufacturing.</P>

고주파 유도가열을 이용한 철강재의 마찰교반용접 특성평가

천현필(Jason Cheon),박태순(Taesoon Park),윤진영(Jin-young Yoon),김철희(Cheolhee Kim) 대한용접·접합학회 2019 대한용접·접합학회지 Vol.37 No.5

Friction stir welding of carbon steel causes tool wear and system deformation issues because of its relatively high strength compared to aluminum. As a countermeasure, additional high-frequency induction heating is suggested to solve this problem. An inline high-frequency induction heating assisted friction stir welding process was studied on 450 MPa and 980 MPa grade carbon steel sheets. As a pre-experiment, the heating performance of the high-frequency induction heating system was quantified. Then the effective welding speed range, vertical load history, and weldment performance were investigated to evaluate the characteristics of the process. Those results were compared with a conventional friction stir welding process conducted under equivalent process conditions. For the 440 MPa steel, about 40% faster maximum welding speed was achieved by applying the 4 kW induction heating. No tensile strength degradation of the weldment was found. Also, the maximum vertical load was decreased by 26% compared to the conventional friction stir welding process. No significant degradation of hardness was observed in the welds on 440 MPa and 980 MPa steel.

산업 현장에서의 마찰교반용접 툴 마모와 용접부 품질의 상관관계

천현필(Jason Cheon) 한국트라이볼로지학회 2022 한국트라이볼로지학회 학술대회 Vol.2022 No.10

레이저빔 용접과 마찰교반용접을 이용한 6천 및 7천계열 알루미늄 판재 접합부의 인장강도비교

천현필(Jason Cheon),강민정(Minjung Kang),윤진영(Jin-young Yoon),김철희(Cheolhee Kim) 대한용접·접합학회 2019 대한용접·접합학회지 Vol.37 No.3

Due to the high thermal diffusivity and metallurgical sensitivity, the proper welding processes of the aluminum are required. The Laser beam welding and friction stir welding processes have been focused as the appropriated welding processes for aluminum. The heat treated 6xxx series and 7xxx series aluminum sheet were welded by the laser beam welding and friction stir welding processes. Also, the effects of heat input through the welding parameters were investigated. The tensile strength of weldments was evaluated respectively and compared by the processes and heat input level. The insignificant tensile strength differences were found for the 6xxx series by the welding processes. However, the friction stir welded 7xxx series weldments were shown 82~89% joint efficiency while laser beam welded weldment were shown 48~58%. Overall, the effect of heat input level was not revealed in this experiment range. The degradations in hardness of weldments tended to be in proportion to the joint efficiency loss.

전산유체역학 기반의 마찰교반용접 공정의 재현 기법과 가능성

천현필(Jason Cheon),윤진영(Jin-Young Yoon),나석주(Suck-Joo Na) 한국자동차공학회 2017 한국자동차공학회 부문종합 학술대회 Vol.2017 No.5

Global Market Analysis for Welding Power Source and Welding Robot (I)

이승재,Cheon Jason,김철희 대한용접접합학회 2020 대한용접·접합학회지 Vol.38 No.3

Welding power source and welding robot are the most important components of welding automation systems. In this paper, we summarized the sales and market revenues of welding power source and welding robot using the mar�ket analysis reports from 2007 to 2017. The analysis was conducted for arc welding and resistance welding, respectively. The power source market of 2017 returned to that of 2007, and the welding robot market of 2017 ap�proximately doubled that of 2007. These market trends are found to be closely related to the major application in�dustries such as the heavy industry and the automotive industry.

The Effect of EN Pulsing Ratio and Repetition Frequency on the Bead Appearance and Microstructure Evolution in Aluminum Welding using Variable Polarity GMAW

Minjung Kang,Jason Cheon,Tae Hyun Lee 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.2

This study addressed the gas metal arc welding (GMAW) of Al 5183 aluminum alloy using variable polarity (VP). The effects of the electrode negative (EN) pulsing ratio and repetition frequency on the geometrical features and microstructural evolution of the deposited materials were investigated and discussed. The current and voltage were manually controlled independently for each phase to evaluate the effect of the polarity change. The influence of phase and its changing frequency on the geometrical features and microstructure evolution were observed. The phase of the electrode affected the arc concentration and changed the amount of the deposited material and the dilution between the substrate. The EN phase is beneficial for making a finer structure than the electrode positive (EP) phase because of the lower heat input per unit mass. In addition, the size of the grains decreased as the phase change frequency increased. When the number of repetitions frequency increased within a cycle, the size of the microstructure was reduced. Consequently, strategies can be established to minimize the microstructure with VP-GMAW welding using a high EN pulsing ratio and low repetition conditions.