| 1. |
- Aryal, Pradip, et al.
(author)
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Comparative study of the main electromagnetic models applied to melt pool prediction with gas metal arc : Effect on flow, ripples from drop impact, and geometry
- 2022
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In: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 194
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Journal article (peer-reviewed)abstract
- The present work concerns the electromagnetic force models in computational fluid dynamics simulations of melt pools produced with electric arcs. These are commonly applied to gas metal arcs with metal transfer, in welding and additive manufacturing. Metal drop impact on the melt pool is thus included in this study. The electromagnetic force models applied in literature use either numerical solutions of Poisson equations or one of the two analytical models developed by Kou and Sun, or Tsao and Wu. These models rely on assumptions for which the effect on the melt pool predictions remains to be understood. The present work thoroughly investigates those assumptions and their effects. It has been supported by dedicated experimental tests that did provide estimates of unknown model parameters and validation data. The obtained results show that the assumptions that fundamentally distinguish these three models change the electromagnetic force, including the relation between its components. These changes, which can also be spatially non-uniform, are large. As a result, these models lead to significantly different recirculation flow pattern, thermal convection, melt pool morphology, bead dimensions, and free surface response to the metal transfer. We conclude by proposing conditions in which each of these models is suited or questionable.
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| 2. |
- Aryal, Pradip, et al.
(author)
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Effect of Substrate Orientation on Melt Pool during Multi-Layer Deposition in V-Groove with Gas Metal Arc
- 2021
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In: Proceedings of the World Congress on Mechanical, Chemical, and Material Engineering. - : Avestia Publishing. - 2369-8136. - 9781927877616
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Conference paper (peer-reviewed)abstract
- Thermo-fluid dynamic and experimental approaches are used to investigate the influence of 20° uphill, downhill and sideway substrate orientation during metal deposition over a previously deposited bead in a V-groove. The computational fluid dynamic model with free surface deformation and metal transfer gives insight into the melt pool flow and causes of defect formation observed on the solidified beads. The experimental metallographs, high-speed images and computational results show good agreement. It is found that the deposition of a second layer on a smooth first layer cooled down to room temperature leads to large changes in melt pool flow pattern at 20° substrate inclination compared to flat condition. It results in undercut and humps with the uphill orientation and undercut with the side inclination. Therefore, lower angle range is necessary for multilayer gas metal arc deposition for these two last configurations.
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| 3. |
- Choquet, Isabelle, et al.
(author)
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A physically based model for thermal plasma arc attachment on a W-ThO2 cathode
- 2016
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In: 2016 IEEE International Conference on Plasma Science (ICOPS).
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Conference paper (peer-reviewed)abstract
- Summary form only given. Arc attachment radius imposed a priori when modelling the coupling between cathode, cathode layer and thermal plasma still hinders models from being predictive, as underlined in a recent review1. The aim of this work was to find a physical element, still lacking in the models, which could contribute in governing the arc attachment. In this study the cathode layer is modeled within the frame of the partial local thermal equilibrium approach1 including the space charge layer, the Knudsen layer and the ionization layer, while the plasma column is assumed to be in local thermal equilibrium. Several modeling assumptions were questioned based on e.g. contradictory assumptions in the literature, or oversimplified physics compared to experimental observations. For testing model and assumptions, 5 mm argon arc test cases with a sharp cathode geometry that have been investigated experimentally in the literature were calculated. Within this framework, the following conclusions were drawn. The space charge emitted electrons is negligible. The Richardson-Dushman emission law supplemented with Schottky correction is used within its domain of validity when applied to thorium doped tungsten cathodes, which are mainly characterized by a field enhanced thermionic emission regime. The radiative heat absorption from the plasma at the cathode surface is not negligible compared to the radiative emission. Ignoring the non-homogeneous structure and composition of a doped tungsten cathode operated in these conditions leads to a large over-estimation of the extent of the arc attachment, and results in an under-estimation of the arc temperature. A cathode model based on physical criteria for taking into account a first level of the cathode inhomogeneity has a significant effect on the arc attachment and on arc properties such as temperature and pressure. The cathode physics is thus an important element to include for obtaining a comprehensive and predictive arc model.
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| 4. |
- Choquet, Isabelle, et al.
(author)
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A predictive model for gas tungsten arc heat source
- 2016
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In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - Lund : Swedish Production Academy. ; , s. 1-10
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Conference paper (peer-reviewed)abstract
- 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.
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| 5. |
- Choquet, Isabelle, et al.
(author)
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Analysis of the Influence of the Composition of the Shielding Gas on Pressure Force and Heat Fluxes in Arc Welding
- 2014
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In: Proceedings of The 6<sup>th</sup> International Swedish Production Symposium 2014. - 9789198097412 ; , s. 1-8
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Conference paper (peer-reviewed)abstract
- A main problem raised by arc welding manufacturing is the determination ofthe optimal process parameters to ensure weld quality as well as resource efficient andsustainable production. To address this problem a better process understanding is required.In this study thermal magneto hydrodynamic modeling of a welding arc is used to reacha deeper insight into the influence of the composition of the shielding gas on the pressureforce and the heat fluxes to a workpiece. The model was implemented in the open sourcesimulation software OpenFOAM. Four different shielding gas mixtures combining argonand carbon dioxide were studied. When increasing the fraction of carbon dioxide the resultsshow a significant increase of the arc velocity and temperature with constriction of thetemperature field, a decrease of the pressure force and a significant increase of the heatfluxes on the base metal.
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| 6. |
- Choquet, Isabelle, et al.
(author)
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Electric welding arc modeling with the solver OpenFOAM - A comparison of different electromagnetic models
- 2011
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In: International Institute of Welding Document No 212-1189-11, July 2011..
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Conference paper (peer-reviewed)abstract
- This study focuses on the modeling of a plasma arc heat source in the context of electric arc welding. The model was implemented in the open source CFD software OpenFOAM-1.6.x, coupling thermal fluid mechanics in three dimensions with electro magnetics. Four different approaches were considered for modeling the electromagnetic fields: i) the three-dimensional approach, ii) the two-dimensional axi-symmetric approach, iii) the electric potential formulation, and iv) the magnetic field formulation as described by Ramírez et al. [1]. The underlying assumptions and the differences between these models are described in detail. Models i) to iii) reduce to the same quasi one-dimensional limit for an axi-symmetric configuration with negligible radial current density, contrary to model iv). Models ii) to iv) do not represent the same physics when the radial current density is significant, such as or an electrode with a conical tip. Models i) to iii) were retained for the numerical simulations. The corresponding results were validated against the analytic solution of an infinite electric rod. Perfect agreement was obtained for all the models tested. The results from the coupled solver (thermal fluid mechanics coupled with electromagnetics) were compared with experimental measurements for Gas Tungsten Arc Welding (GTAW). The shielding gas was argon, the arc was short (2mm), the electrode tip was conical, and the configuration was axi-symmetric. The boundary conditions were specified at the anode and cathode surfaces. Models i) and ii) lead to the same results, but not the model iii). Model iii) neglects the radial current density component, resulting in a poor estimation of the magnetic field, and in turn of the arc fluid velocity. The limitations of the coupled solver were investigated changing the gas composition, and using different boundary conditions. The boundary conditions, difficult to measure and to estimate a priori, significantly affect the simulation results.
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| 7. |
- Choquet, Isabelle, et al.
(author)
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Magnetic field models for high intensity arcs, applied to welding - A comparison between three different formulations
- 2013
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In: 9th International Conference on Trends in Welding Research; Chicago, IL; United States; 4 June 2012 through 8 June 2012. - 9781627089982 ; , s. 876-885
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Conference paper (peer-reviewed)abstract
- 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.
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| 8. |
- Choquet, Isabelle, 1965-, et al.
(author)
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Modeling and simulation of a heat source in electric arc welding
- 2011
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In: Proceedings from the 4th Swedish Production Symposium, Lund, Sweden. ; , s. 202-211, s. 201-211
-
Conference paper (peer-reviewed)abstract
- This study focused on the modeling and simulation of a plasma heat source applied toelectric arc welding. The heat source was modeled in three space dimensions couplingthermal fluid mechanics with electromagnetism. Two approaches were considered forcalculating the magnetic field: i) three-dimensional, and ii) axi-symmetric. The anodeand cathode were treated as boundary conditions. The model was implemented in theopen source CFD software OpenFOAM-1.6.x. The electromagnetic part of the solverwas tested against analytic solution for an infinite electric rod. Perfect agreement wasobtained. The complete solver was tested against experimental measurements for GasTungsten Arc Welding (GTAW) with an axi-symmetric configuration. The shielding gaswas argon with thermodynamic and transport properties covering a temperature rangefrom 200 to 30 000 K. The numerical solutions then depend greatly on the approachused for calculating the magnetic field. The axi-symmetric approach indeed neglectsthe radial current density component, mainly resulting in a poor estimation of the arcvelocity. Various boundary conditions were set on the anode and cathode. Theseconditions, difficult to measure and to estimate a priori, significantly affect the plasmaheat source simulation results. Solution of the temperature and electromagnetic fieldsin the electrodes will thus be included in the forthcoming developments.
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| 9. |
- Choquet, Isabelle, 1965-, et al.
(author)
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Numerical simulation of Ar-x%CO2 shielding gas and its effect on an electric welding arc
- 2011
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In: IIW Commission XII / SG 212 Intermediate meeting, University West, Trollhättan, Sweden, 21 - 23 March 2011, IIW Doc. XII-2017-11. ; , s. 1-12
-
Conference paper (other academic/artistic)abstract
- 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 mixtures of 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.
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| 10. |
- Choquet, Isabelle, 1965-, et al.
(author)
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On the choice of electromagnetic model for shorthigh-intensity arcs, applied to welding
- 2012
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In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 45:20, s. 205203-
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Journal article (peer-reviewed)abstract
- 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.
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