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  • 1.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics, Gothenburg, Sweden.
    A predictive model for gas tungsten arc heat source2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-10Conference paper (Refereed)
    Abstract [en]

    Gas tungsten arcs are used as heat sources in production processes such as welding and metal deposition.However, the most advanced of the existing gas tungsten arc models still lack predicting the arc temperature observed experimentally, unless imposing a priori the extent of the cathode arc attachment.Possible causes of this problem were investigated. It was concluded that the physical state of the arcing gas tungsten cathode was too simplified by the existing models. This oversimplification results in an overestimation of the cathode arc attachment area and an underestimation of the arc temperature field.An improved model was developed based only on physical criteria. It was tested by comparison with experimental measurements available in the literature. Good agreement with the temperature measured on the cathode surface and within the arc were obtained.

  • 2.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology.
    Electric welding arc modeling with the three-dimensional solver OpenFOAM: A comparison of different electromagnetic models2011In: 64 th Annual Assembly and International Conference of International Institute of Welding, 64th IWW: Chennai, 17-22 july, 2011. Working group 212, 2011, p. 212-1189-11-1-212-1189-11-16Conference paper (Other academic)
    Abstract [en]

    This study focuses on the modeling of a plasma arc heat source in the context ofelectric arc welding. The model was implemented in the open source CFD softwareOpenFOAM-1.6.x, coupling thermal fluid mechanics in three dimensions with electromagnetics.Different approaches were considered for modeling the electromagneticfields: i) the three-dimensional approach, ii) the two-dimensional axi-symmetric approach,iii) the electric potential formulation, and iv) the magnetic field formulation asdescribed by Ramírez et al. [1]. The underlying assumptions and the differencesbetween these models are detailed. The models i) to iii) reduce to the same quasione-dimensional limit for an axi-symmetric configuration with negligible radial currentdensity, contrary to the formulation iv). The models ii) to iv) cannot represent the samephysics when the radial current density is significant, such as for a short arc or anelectrode with a conical tip. The models i) to iii) were retained for doing numerical simulations.The corresponding solvers were tested against analytic solution for an infiniteelectric rod. Perfect agreement was obtained for all the models tested. The completesolver (thermal fluid coupled with electromagnetics) was tested against experimentalmeasurements for Gas Tungsten Arc Welding (GTAW). The shielding gas was argon,the arc was short (2mm), the electrode tip conical, and the configuration axi-symmetric.Anode and cathode were treated as boundary conditions. The models i) and ii) lead tothe same results, but not the formulation iii). It indeed neglects the radial current densitycomponent, resulting in a poor estimation of the magnetic field, and in turn of thearc velocity. Limitations of the complete solver were investigated changing also the gascomposition, and testing boundary conditions. These conditions, difficult to measureand to estimate a priori, significantly affect the simulation results.

  • 3.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics,412 96 Gothenburg, Sweden.
    On the choice of electromagnetic model for shorthigh-intensity arcs, applied to welding2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 20, p. 205203-Article in journal (Refereed)
    Abstract [en]

    Four different approaches were considered for modelling the electromagneticfields of high-intensity electric arcs: i) the three-dimensional model, ii) the twodimensionalaxi-symmetric model, iii) the electric potential formulation, and iv) themagnetic field formulation. The underlying assumptions and the differences betweenthese models are described in detail. Models i) to iii) reduce to the same limit for anaxi-symmetric configuration with negligible radial current density, contrary to modeliv). Models i) to iii) were retained and implemented in the open source CFD softwareOpenFOAM. The simulation results were first validated against the analytic solutionof an infinite electric rod. Perfect agreement was obtained for all the models tested.The electromagnetic models i) to iii) were then coupled with thermal fluid mechanicsin OpenFOAM, and applied to the calculation of an axi-symmetric Gas Tungsten ArcWelding (GTAW) test case with short arc (2mm) and truncated conical electrode tip.Models i) and ii) lead to the same simulation results, but not model iii). Model iii)is suited in the specific limit of long axi-symmetric arc, with negligible electrode tipeffect. For short axi-symmetric arc, the more general axi-symmetric formulation ofmodel ii) should instead be used.

  • 4.
    Choquet, Isabelle
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Javidi-Shirvan, Alireza
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics, .
    Magnetic field models for high intensity arcs, applied to welding: A comparison between three different formulations2013In: ASM Proceedings of the International Conference: Trends in Welding Research 2013, Chicago, IL: ASM International, 2013, p. 876-885Conference paper (Refereed)
    Abstract [en]

    Most simulation studies done to deeper understand high-intensity welding arcs address axi-symmetric configurations and use the electric potential formulation. This formulation involves the assumption of a one-dimensional magnetic field. The assumption is justified in its original frame: rather long arcs (about 10 mm), and when the electrode tip is excluded from the computational domain. However, arcs applied to welding are shorter, and the electrode geometry is important to take into account. The present work questions the assumption of a one-dimensional magnetic field for simulating short welding arcs. We have compared three different approaches for modeling the magnetic field: three-dimensional, two-dimensional axi-symmetric, and the electric potential formulation. These models have been applied to water cooled anode Gas Tungsten Arc Welding (GTAW) test cases with truncated conical electrode tip (tip radius of 0.5 and 0.2 mm) and various arc lengths (2, 3 and 5 mm). For the axi-symmetric cases studied in the present work, the three- and two-dimensional models give exactly the same results. The one-dimensional simplification of the magnetic field turns out to have a significant unfavorable effect on the simulation results. For axi-symmetric welding applications, it is argued that the two-dimensional axi-symmetric formulation should be used. Copyright © 2013 ASM International® All rights reserved.

  • 5.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Production Engineering.
    Stenbacka, Nils
    University West, Department of Engineering Science, Division of Production Engineering.
    Numerical simulation of Ar-x%CO2 shielding gas and its effect on an electric welding arc2011In: IIW Commission XII Doc. XII-2017-11, 2011, p. 1-12Conference paper (Other academic)
    Abstract [en]

    This study focuses on the simulation of a plasma arc heat source in the context of electric arc welding. The simulation model was implemented in the open source CFD software OpenFOAM-1.6.x, in three space dimensions, coupling thermal fluid mechanics with electromagnetism. Two approaches were considered for calculating the magnetic field: i) the three-dimensional approach, and ii) the so-called axisymmetric approach. The electromagnetic part of the solver was tested against analytic solution for an infinite electric rod. Perfect agreement was obtained. The complete solver was tested against experimental measurements for Gas Tungsten Arc Welding (GTAW) with an axisymmetric configuration. The shielding gas was argon, and the anode and cathode were treated as boundary conditions. The numerical solutions then depend significantly on the approach used for calculating the magnetic field. The so-called axisymmetric approach indeed neglects the radial current density component, mainly resulting in a poor estimation of the arc velocity. Plasma arc simulations were done for various Ar-x%CO2 shielding gas compositions: pure argon (x=0), pure carbon dioxide (x=100), and mixturesof these two gases with x=1 and 10% in mole. The simulation results clearly show that the presence of carbon dioxide results in thermal arc constriction, and increased maximum arc temperature and velocity. Various boundary conditions were set on the anode and cathode (using argon as shielding gas) to evaluate their influence on the plasma arc. These conditions, difficult to measure and to estimate a priori, significantly affect the heat source simulation results. Solution of the temperature and electromagnetic fields in the anode and cathode will thus be included in the forthcoming developments.

  • 6.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Welding Technology.
    Modelling of cathode-plasma interaction in short high-intensity electric arc: Application to Gas Tungsten Arc Welding2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In arc welding the quality of the weld is strongly influenced by the thermal history of the workpiece which is itself governed by the electric arc heat source. The models for predicting weld properties thus need a good evaluation of the distribution of the heat input from thearc to the workpiece. To have a predictive model of arc heat source it is necessary to take into account the cathode and its coupling with the plasma. The coupling allows to calculate the temperature and current density distributions along the cathode surface rather than prescribing them. This thesis focuses on the arc-cathode coupling for a plasma assumed to be in local thermal equilibrium. A self-consistent coupling boundary model for high-intensity electric arc on a refractory cathode (thoriated tungsten) was developed accounting for the physics of the sub-layers of the cathode layer and the non-uniformity of the cathode surface physical state. The cathode layer model accounts for the non-equilibria in the cathode layer. It was tested in one-dimensional calculations and then extended to a cathode-plasma coupling boundary condition for gas tungsten arc implemented in OpenFOAM. Different modelling assumptions commonly used for developing the model were questioned and investigated. It was checked that the secondary electron emission is negligible compared to the effect of emitted electrons and ions. It was verified that it is justified to neglect the space charge of emitted electron when calculating the cathode surface electric field. It was verified that Richardson-Dushman electron emission law supplemented with Schottky correction is used within its domain of validity in GTA applications even for low work function emitters. It was shown that the radiative absorption of the cathode surface is not negligible compared to the radiative emission. The cathode layer model was also further developed to take into account the in homogeneity of the cathode material. It was shown that the cathode in homogeneityhas a significant effect on the size of the arc attachment and consequently on the cathode surface and the plasma temperature. Good agreement was obtained with the measured cathode surface and plasma temperatures without imposing any adjustable parameters. The results showed that the proposed model, which is only based on physical principles, is ableto predict the trends observed experimentally.

  • 7.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Modelling of Electric Arc Welding: arc-electrode coupling2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Arc welding still requires deeper process understanding and more accurateprediction of the heat transferred to the base metal. This can be provided by CFD modelling.Most works done to model arc discharge using CFD consider the arc corealone. Arc core simulation requires applying extrapolated experimental data asboundary conditions on the electrodes. This limits the applicability. To become independent of experimental input the electrodes need to be included in the arcmodel. The most critical part is then the interface layer between the electrodesand the arc core. This interface is complex and non-uniform, with specific physicalphenomena.The present work reviews the concepts of plasma and arc discharges that areuseful for this problem. The main sub-regions of the model are described, andtheir dominant physical roles are discussed.The coupled arc-electrode model is developed in different steps. First couplingsolid and fluid regions for a simpler problem without complex couplinginterface. This is applied to a laser welding problem using the CFD softwareOpenFOAM. The second step is the modelling of the interface layer betweencathode and arc, or cathode layer. Different modelling approaches available inthe literature are studied to determine their advantages and drawbacks. One ofthem developed by Cayla is used and further improved so as to satisfy the basicprinciples of charge and energy conservation in the different regions of thecathode layer. A numerical procedure is presented. The model, implementedin MATLAB, is tested for different arc core and cathode conditions. The maincharacteristics calculated with the interface layer model are in good agreementwith the reference literature. The future step will be the implementation of theinterface layer model in OpenFOAM.

  • 8.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    A review of cathode-arc coupling modeling in GTAW2016In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, no 4, p. 821-835Article in journal (Refereed)
    Abstract [en]

    Material properties of welds are strongly influenced by the thermal history, including the thermo-fluid and electromagnetic phenomena in the weld pool and the arc heat source. A necessary condition for arc heat source models to be predictive is to include the plasma column, the cathode, and the cathode layer providing their thermal and electric coupling. Different cathode layer models based on significantly different physical assumptions are being used. This paper summarizes today’s state of the art of cathode layer modeling of refractory cathodes used in GTAW at atmospheric pressure. The fundamentals of the cathode layer and its physics are addressed. The main modeling approaches, namely (i) the diffusion approach, (ii) the partial LTE approach, and (iii) the hydrodynamic approach are discussed and compared. The most relevant publications are systematically categorized with regard to the respective physical phenomena addressed. Results and process understanding gained with these models are summarized. Finally, some open questions are underlined.

  • 9.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Effect of cathode model on arc attachment for short high-intensity arc on a refractory cathode2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 3 November 2016, p. 1-17, article id 485201Article in journal (Other academic)
    Abstract [en]

    Various models coupling the refractory cathode, the cathode sheath and the arc at atmospheric pressure exist. They assume a homogeneous cathode with a uniform physical state, and differ by the cathode layer and the plasma arc model. However even the most advanced of these models still fail in predicting the extent of the arc attachment when applied to short high-intensity arcs such as gas tungsten arcs. Cathodes operating in these conditions present a non-uniform physical state. A model taking into account the first level of this non-homogeneity is proposed based on physical criteria. Calculations are done for 5 mm argon arcs with a thoriated tungsten cathode. The results obtained show that radiative heating and cooling of the cathode surface are of the same order. They also show that cathode inhomogeneity has a significant effect on the arc attachment, the arc temperature and pressure. When changing the arc current (100 A, 200 A) the proposed model allows predicting trends observed experimentally that cannot be captured by the homogeneous cathode model unless restricting a priori the size of the arc attachment. The cathode physics is thus an important element to include to obtain a comprehensive and predictive arc model

  • 10.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Modelling of electrode-arc coupling in electric arc welding2014In: Proceedings of The 6th International Swedish Production Symposium 2014 16-18 September 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Modelling of the arc in electric arc welding is significant to achieve a better pro-cess understanding, thus gain better weld quality and a more efficient production process.It requires knowing the conditions at the surfaces of the anode and cathode. These condi-tions are very difficult to set from measurements and should be calculated. This requiresmodelling the complex physics of the electrode layer coupling electrode and arc. Thispaper presents a self-consistent electrode layer model that 1) is suited to welding applica-tions, 2) accounts for the known physics taking place, and 3) satisfies the basic conservationrequirements. The model is tested for different conditions. Its potentiality for welding ap-plications is shown through calculations coupling plasma arc, electrode and cathode layermodels. The calculations are done for both tungsten and thoriated tungsten electrode.

  • 11.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Mechanical Engineering. University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of technology, Applied Mechanics.
    Numerical modelling of shielding gas flow and heat transfer in laser welding process2012In: Proceedings of the 5th International Swedish Production Symposium, SPS12 / [ed] The Swedish Production Academy on October 2012, Linköping, 2012, , p. 7p. 1-7Conference paper (Refereed)
    Abstract [en]

    In the present work a three-dimensional model has been developed to study shieldinggas flow and heat transfer in a laser welding process using computational fluid dynamics.This investigation was motivated by problems met while using an optical system totrack the weld path. The aim of this study was to investigate if the shielding gas flowcould disturb the observation area of the optical system. The model combines heatconduction in the solid work piece and thermal flow in the fluid region occupied by theshielding gas. These two regions are coupled through their energy equations so asto allow heat transfer between solid and fluid region. Laser heating was modelled byimposing a volumetric heat source, moving along the welding path. The model wasimplemented in the open source software OpenFOAM and applied to argon shieldinggas and titanium alloy Ti6Al4V base metal. Test cases were done to investigate theshielding gas flow produced by two components: a pipe allowing shielding the melt,and a plate allowing shielding the weld while it cools down. The simulation results confirmedthat these two components do provide an efficient shielding. They also showedthat a significant amount of shielding gas flows towards the observation area of the opticalsystem intended to track the weld path. This is not desired since it could transportsmoke that would disturb the optical signal. The design of the shielding system thusneeds to be modified.

  • 12.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Mechanics and Maritime Sciences, 412 96 Gothenburg, Sweden.
    Jasak, Hrvoje
    University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, 10 000 Zagreb, Croatia.
    Coupling boundary condition for high-intensity electric arc attached on a non-homogeneous refractory cathode2018In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 222, p. 31-45Article in journal (Refereed)
    Abstract [en]

    The boundarycoupling high-intensity electricarc and refractory cathode is characterized bythree sub- layers: the cathode sheath,the Knudsen layerand the pre-sheath. A self-consistent coupling boundarycondition accounting for these three sub-layers is presented; its novel propertyis to take into account a non-uniform distribution of electronemitters on the surface of the refractory cathode. This non- uniformity is due to cathode non-homogeneity induced by arcing.The computational model is appliedto a one-dimensional test case to evaluate the validity of different modelingassumptions. It is also applied coupling a thoriated tungstencathode with an argon plasma(assumed to be in local thermal equilibrium) to compare the calculation results with uniform and non-uniform distribution of the electron emitters to experimental measurements. The resultsshow that the non-uniformity of the electronemitters’ distribution has a significant effect on the calculated properties. It leads to good agreementwith the cathode surfacetemperature, and with the plasmatemperature in the hottest region.Some differences are observedin colder plasmaregions, where deviation from local thermalequilibrium is known to occur.

  • 13.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Jasak, Hrvoje
    Chalmers University of Technology.
    Coupling boundary condition for high-intensity electricarc attached on a non-homogeneous refractory cathode2016In: Article in journal (Other academic)
1 - 13 of 13
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