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  • 1.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Clement, Uta
    Numerical and experimental study of Ni-particle impact on a ti-surfaceIn: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016Article in journal (Refereed)
  • 2.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Numerical and Experimental Study of Ni-Particle Impact On A Ti-Surface2007In: Proceedings of the International Thermal Spray Conference: May 2007, Beijing, China, ASM International , 2007, p. 219-224Conference paper (Refereed)
  • 3.
    Beaubert, F.
    et al.
    TEMPO, UVHC, Campus Mont Houy, 59313 Valenciennes Cedex 9, France.
    Pálsson, H.
    University of Iceland, Sæmundargötu 2, Reykjavík 101, Iceland.
    Lalot, S.
    EMPO, UVHC, Campus Mont Houy, Valenciennes Cedex 9, France.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Bauduin, H.
    EMPO, UVHC, Campus Mont Houy, Valenciennes Cedex 9, France.
    Fundamental mode of freely decaying laminar swirling flows2016In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 40, no 13-14, p. 6218-6233Article in journal (Refereed)
    Abstract [en]

    Abstract A detailed study of a swirling flow in a tube is presented in the first part of the paper. A simplified analytical solution of the governing equations indicates specific modes of the tangential velocity and that the decay of the swirl effect is exponential. The problem is then solved in three dimensions using computational fluid dynamics (CFD) and a comparison with analytical expressions shows that the CFD code is reliable in terms of accuracy. The CFD results confirm that a fundamental swirling mode is reached within a short distance from the inlet. The torque swirl number is introduced to physically estimate the intensity of the swirl. A companion value is given: it is the average deviation.

  • 4.
    Beaubert, Francois
    et al.
    Valenciennes University.
    Pálsson, Halldór
    University of Iceland.
    Lalot, Sylvain
    Valenciennes University.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Bauduin, Hadrian
    Valenciennes University.
    Design of a device to induce swirling flow in pipes: A rational approach2015In: Comptes rendus. Mecanique, ISSN 1631-0721, E-ISSN 1873-7234, Vol. 343, no 1, p. 1-12Article in journal (Refereed)
    Abstract [en]

    In this study, a rational approach is proposed to design a device for inducing swirling flow in heat exchanger pipes, for improved efficiency in the laminar regime. First, 2D computational fluid dynamics results lead to select, among four profiles, the blade profile with the most favorable lift to drag ratio. Then, the fluid flow in the swirler made with the selected blade profile is simulated in 3D, for Reynolds numbers ranging from 50 to 1600. Based on the simulation results, an analytic approximation of the evolution of the tangential fluid velocity is proposed as a function of the Reynolds number.

  • 5.
    Chazelas, Christophe
    et al.
    European Ceramic Center, SPCTS CNRS UMR 7315, University of Limoges, Limoges, France.
    Trelles, Juan Pablo
    Mechanical Engineering, University of Massachusetts Lowell, Lowell, USA.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Vardelle, Armelle
    European Ceramic Center, SPCTS CNRS UMR 7315, University of Limoges, Limoges, France.
    Main issues for a fully predictive plasma spray torch model and numerical considerations2017In: Plasma chemistry and plasma processing, ISSN 0272-4324, E-ISSN 1572-8986, Vol. 37, no 3, p. 627-651Article in journal (Refereed)
    Abstract [en]

    Plasma spray is one of the most versatile and established techniques for the deposition of thick coatings that provide functional surfaces to protect or improve the performance of the substrate material. However, a greater understanding of plasma spray torch operation will result in improved control of process and coating properties and in the development of novel plasma spray processes and applications. The operation of plasma torches is controlled by coupled dynamic, thermal, chemical, electromagnetic, and acoustic phenomena that take place at different time and space scales. Computational modeling makes it possible to gain important insight into torch characteristics that are not practically accessible to experimental observations, such as the dynamics of the arc inside the plasma torch. This article describes the current main issues in carrying out plasma spray torch numerical simulations at a high level of fidelity. These issues encompass the use of non-chemical and non-thermodynamic equilibrium models, incorporation of electrodes with sheath models in the computational domain, and resolution of rapid transient events, including the so-called arc reattachment process. Practical considerations regarding model implementation are also discussed, particularly the need for the model to naturally reproduce the observed torch operation modes in terms of voltage and pressure fluctuations.

  • 6.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Gas tungsten arc models including the physics of the cathode layer: remaining issues2018In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 1, p. 177-196Article in journal (Refereed)
    Abstract [en]

    A recent review pointed out that the existing models for gas tungsten arc coupling the electrode (a cathode) and the plasma are not yet complete enough. Their strength is to predict with good accuracy either the electric potential or the temperature field in the region delimited by the electrode and the workpiece. Their weakness is their poor ability to predict with good accuracy these two fields at once. However, both of these fields are important since they govern the heat flux to the workpiece through current density and temperature gradient. New developments have been made since then. They mainly concern the approaches addressing the electrode sheath (or space charge layer) that suffered from an underestimation of the arc temperature. These new developments are summarized and discussed, the modelling assumptions are examined, and important modelling issues that remain unexplored are underlined.

  • 7.
    Choquet, Isabelle
    University West, Department of Informatics and Mathematics.
    Nozzle exit geometry and lump formation in atmospheric plasma spraying2005In: International Thermal Spray Conference: Basel, Switzerland, May, ASM International , 2005, p. 259-264Conference paper (Other academic)
    Abstract [en]

    Plasma spraying operations performed with high carrier gas flow rate may improve the coating properties but they can also lead to lump formation and thus coating defects. The damaged work piece must then be stripped and re-coated, which implies a considerable waste in terms of coating powder, energy and time. The aim of this study was to determine the cause of the lumps, and propose process modifications for avoiding their formation while keeping the coating quality. Numerical simulations based on 3D turbulent Navier-Stokes equations in local thermal and chemical equilibrium were carried out to understand the problem and estimate the feasibility of the proposed solutions. The computational results were supplemented by experiments for validation. A first set of investigations was focused on the location and orientation of the powder port injector. It turned out that it was not possible to keep the coating quality while avoiding lump formation by simply moving the powder injector. A new geometry of the nozzle exit was then designed and successfully tested for a first application with Ni-5Al powder used in production. 

  • 8.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Johansson, J.
    Wigren, J.
    New powder port holder geometry to avoid lump formation in APS2005In: 17th international symposium on plasma chemistry (ISPC 17) :: Toronto, Canada, August 7th – 12th, 2005, 2005, p. OP7. 1-6Conference paper (Other academic)
    Abstract [en]

    A new geometry of the powder port ring holder used in atmospheric plasma spraying has recently been designed to avoid lump formation, and successfully tested for a set of process parameters associated with Ni-5Al powder used in production to form bond coat [1]. But with ZrO 2 powder used to made top coat, improvements were not enough satisfactory. Here, we investigate numerically the cause of the remaining defects, and further improve the ring geometry to prevent lump from forming in any part of the coating.

  • 9.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Johansson, Jimmy
    Volvo Aero Corporation, Trollhättan.
    Wigren, Jan
    Volvo Aero Corporation, Trollhättan.
    Clogging and lump formation during atmospheric plasma spraying with powder injection downstream the plasma gun2007In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 16, no 4, p. 512-523Article in journal (Refereed)
    Abstract [en]

    This study aimed to numerically and experimentally investigate lump formation during atmospheric plasma spraying with powder injection downstream the plasma gun exit. A first set of investigations was focused on the location and orientation of the powder port injector. It turned out impossible to keep the coating quality while avoiding lumps by simply moving the powder injector. A new geometry of the powder port ring holder was designed and optimized to prevent nozzle clogging, and lump formation using a gas screen. This solution was successfully tested for applications with Ni-5wt.%Al and ZrO2-7wt.%Y2O3 powders used in production. The possible secondary effect of plasma jet shrouding by the gas screen, and its consequence on powder particles prior to impact was also studied.

  • 10.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Degond, Pierre
    Universit´e Paul Sabatier, Mathématiques pour l’Industrie et la Physique.
    Lucquin-Desreux, Brigitte
    Universit´e Pierre et Marie Curie-Paris 6, Laboratoire Jacques-Louis Lions.
    A strong ionization model in plasma physics2009In: Mathematical and Computer Modelling, Vol. 49, no 1-2, p. 88-113Article in journal (Refereed)
  • 11.
    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.

  • 12.
    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.

  • 13.
    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.

  • 14.
    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.

  • 15.
    Choquet, Isabelle
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Lucquin-Desreuw, B
    Hydrodynamic limit for an arc discharge at atmospheric pressure2005In: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 119, no 1-2, p. 197-239Article in journal (Refereed)
    Abstract [en]

    In this paper we study a partially ionized plasma that corresponds to an arc discharge at atmospheric pressure. We derive an inviscid hydrodynamic/diffusion limit, characterized by two temperatures, from a system of Boltzmann type transport equations modelling that plasma problem. The original property of this system is that impact ionization is a leading order collisional process. As a consequence, the density of electrons is given in terms of the density of the other species (and its temperature) via a Saha law.

  • 16.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science.
    Lucquin-Desreux, Brigitte
    University Pierre and Marie Curie, Paris, France.
    Non equilibrium ionization in magnetized two-temperature thermal plasma2011In: Kinetic and Related Models, ISSN 1937-5093, E-ISSN 1937-5077, ISSN 1, Vol. 4, no 3, p. 669-700Article in journal (Refereed)
    Abstract [en]

    A thermal plasma is studied accounting for both impact ionization, and an electromagnetic field. This plasma problem is modeled based on a system of Boltzmann type transport equations. Electron-neutral collisions are assumed to be much more frequently elastic than inelastic, to complete previous investigations of thermal plasma . A viscous hydrodynamic/diffusion limit is derived in two stagesdoing an Hilbert expansion and using the  Chapman-Enskog method. The resultant viscous fluid model is characterized by two temperatures, and non equilibrium ionization. Its diffusion coefficients depend on the magnetic field, and can be computed explicitely.

  • 17.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics, Gothenburg.
    Analysis of the Influence of the Composition of the Shielding Gas on Pressure Force and Heat Fluxes in Arc Welding2014In: Proceedings of The 6th International Swedish Production Symposium 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    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.

  • 18.
    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.

  • 19.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology.
    Sass-Tisovskaya, Margarita
    University West, Department of Engineering Science, Division of Production Engineering.
    Modeling and simulation of a heat source in electric arc welding2011In: SPS11 : The 4th International Swedish Production Symposiom: Lund, 3-5 maj, 2011, 2011, p. 201-211Conference paper (Refereed)
    Abstract [en]

    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.

  • 20.
    Choquet, Isabelle
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Wigren, J
    Deposition Rate Increase in APS Processes by Means of Multiple Injection Ports2004In: Thermal Spray 2004: Advances in Technology and Application: Proceedings of the International Thermal Spray Conference 10–12 May 2004, Osaka, Japan, 2004, p. 691-695Conference paper (Other academic)
  • 21.
    Freton, Pierre
    et al.
    University Paul Sabatier, Toulouse, France.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Gonzales, Jean-Jacques
    University Paul Sabatier, Toulouse, France.
    Teulet, Philippe
    University Paul Sabatier, Toulouse, France.
    Improvement of a pseudo kinetic method for the calculation of a two-temperature thermal plasma composition2013In: Proceedings of the XXth Symposium on Physics of Switching Arc, 2013, p. 139-142Conference paper (Refereed)
    Abstract [en]

    This paper proposes an improved Saha law for calculating the 2T composition of an Argon thermal plasma. This law is based on a simplified kinetic approach. The obtainedresults are compared with other laws from the literature (Van de Sanden, Pseudokinetic) and provide a satisfying qualitative behaviour.

  • 22.
    Freton, Pierre
    et al.
    Paul Sabatier University, Toulouse, France.
    Gonzales, Jean-Jacques
    Paul Sabatier University, Toulouse, France.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Mougenot, Jacques
    Paul Sabatier University, Toulouse, France.
    Discussion sur les différentes formulations des équations de l´énergie dans les modèles de plasmas thermiques à deux températures2013Conference paper (Other academic)
    Abstract [fr]

    Pour modéliser un plasma thermique à deux températures, les travaux de la littérature proposent en général de résoudre une équation pour l’énergie des électrons et une autre pour celle des lourds. Néanmoins, tous les auteurs ne sont pas d’accord sur une formulation et diverses écritures de ces deux équations de l'énergie peuvent être trouvées dans la littérature. Les principales différences concernent deux termes : le terme correspondant à l'énergie d'ionisation et le terme relatif à la part de conductivité thermique réactive. Suivant les auteurs ces deux termes peuvent être attribués, indifféremment à l’équation de l’énergie régissant la température des particules lourdes ou celle des électrons.

      Afin de nous positionner et éclaircir ce point, nous proposons de développer théoriquement les deux équations de l'énergie en repartant de l'équation de Boltzmann et de ses moments. Les résultats obtenus avec la formulation proposée sont alors comparés avec ceux obtenus avec les formulation de la littérature.

  • 23.
    Gaudiuso, Caterina
    et al.
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, Via Amendola 173, Bari, Italy.
    Giannuzzi, Giuseppe
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, Via Amendola 173, Bari, Italy.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Lugarà, Pietro Mario
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, Via Amendola 173, Bari, Italy.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems.
    Incubation effect in burst mode fs-laser ablation of stainless steel samples2018In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 10520, article id 105200AArticle in journal (Refereed)
    Abstract [en]

    We report on an experimental study of the incubation effect during irradiation of stainless steel targets with bursts of femtosecond laser pulses at 1030 nm wavelength and 100 kHz repetition rate. The bursts were generated by splitting the pristine 650-fs laser pulses using an array of birefringent crystals which provided time separations between sub-pulses in the range from 1.5 ps to 24 ps. We measured the threshold fluence in Burst Mode, finding that it strongly depends on the bursts features. The comparison with Normal Pulse Mode revealed that the existing models introduced to explain the incubation effect during irradiation with trains of undivided pulses has to be adapted to describe incubation during Burst Mode processing. In fact, those models assume that the threshold fluence has a unique value for each number of impinging pulses in NPM, while in case of BM we observed different values of threshold fluence for fixed amount of sub-pulses but different pulse splitting. Therefore, the incubation factor coefficient depends on the burst features. It was found that incubation effect is higher in BM than NPM and that it increases with the number of sub-pulses and for shorter time delays within the burst. Two-Temperature-Model simulations in case of single pulses and bursts of up to 4 sub-pulses were performed to understand the experimental results. © Copyright SPIE.

  • 24.
    Gaudiuso, Caterina
    et al.
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy & Università degli Studi di Bari, Dipartimento Interuniversitario di Fisica, via Amendola 173, Bari, Italy .
    Giannuzzi, Giuseppe
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy & Università degli Studi di Bari, Dipartimento Interuniversitario di Fisica, via Amendola 173, Bari, Italy.
    Volpe, Annalisa
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy.
    Lugarà, Pietro Mario
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy & Università degli Studi di Bari, Dipartimento Interuniversitario di Fisica, via Amendola 173, Bari, Italy.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy.
    Incubation during laser ablation with bursts of femtosecond pulses with picosecond delays2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 4, p. 3801-3813Article in journal (Refereed)
    Abstract [en]

    Abstract: We report on an experimental investigation of the incubation effect during irradiation of stainless steel with bursts of ultrashort laser pulses. A series of birefringent crystals was used to split the pristine 650-fs pulses into bursts of up to 32 sub-pulses with time separations of 1.5 ps and 3 ps, respectively. The number of selected bursts was varied between 50 and 1600. The threshold fluence was measured in case of Burst Mode (BM) processing depending on the burst features, i.e. the number of sub-pulses and their separation time, and on the number of bursts. We found as many values of threshold fluence as the combinations of the number of bursts and of sub-pulses constituting the bursts set to give the same total number of impinging sub-pulses. However, existing incubation models developed for Normal Pulse Mode (NPM) return, for a given number of impinging pulses, a constant value of threshold fluence. Therefore, a dependence of the incubation coefficient with the burst features was hypothesized and experimentally investigated. Numerical solutions of the Two Temperature Model (TTM) in case of irradiation with single bursts of up to 4 sub-pulses have been performed to interpret the experimental results. © 2018 Optical Society of America.

  • 25.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, Dirk
    The University of Manchester, School of Materials, Manchester M13 9PL, UK.
    Roy, Matthew J.
    The University of Manchester, School of Mechanical, Aerospace and Civil Engineering,Manchester M13 9PL, UK.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients2017In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 121, no May, p. 11-23Article in journal (Refereed)
    Abstract [en]

    This paper introduces a novel arc heat treatment technique to produce samples with graded microstructures through the application of controlled temperature gradients. Steady state temperature distributions within the sample can be achieved and maintained, for times ranging from a few seconds to several hours. The technique reduces the number of samples needed to characterize the response of a material to thermal treatments, and can consequently be used as a physical simulator for materials processing. The technique is suitable for conventional heat treatment analogues, welding simulations, multi-step heat treatments, and heat treatments with controlled heating and cooling rates. To demonstrate this technique, a super duplex stainless steel was treated with a stationary TIG arc, to confirm the relationship between generated steady-state temperature fields, microstructure development, hardness, and sensitization to corrosion. Metallographic imaging and hardness mapping provided information about graded microstructures, confirming the formation of secondary phases and microstructure sensitization in the temperature range 850–950 °C. Modelling of temperature distributions and thermodynamic calculations of phase stabilities were used to simulate microstructure development and associated welding cycles.

  • 26.
    Hurtig, Kjell
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter2015In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29, 2015, JOM-institute , 2015, p. 1-19Conference paper (Refereed)
    Abstract [en]

    A comprehensive model on heat transfer in welded plates is able to calculate the amount of heat losses from the surfaces. A model demands as input parameter the amount of heat delivered to the plate, independently of any loss (called here gross heat input for clarity). However, the great discrepancies among the results of calorimetric measurements have left many researchers skeptical about using this parameter in modeling as absolute term. The objective of this work was to assess the use of a water-cooled stationary anode calorimeter to obtain not only arc efficiency, but also gross heat input. A series of tests was carried out to determine the effect of current, material type and water flow rate on the calorimeter performance, as well as to evaluate some measures for reducing the calorimeter intrinsic errors. Finally, a sensitivity test was conducted to estimate the effect of measurement inaccuracies on the absorbed heat and arc efficiency values. The results showed that this calorimetric approach is a simple way for measuring gross heat inputs in arc welding. Nevertheless some improvement to reduce heat losses from the top surface and boost heat sinking from the opposite surface of the test coupon must be applied. This calorimeter is, on the other hand, highly sensitive to the parameter measurements, leading to errors up to ± 0.09 in arc efficiency determination if the instrument is not properly calibrated and installed.

  • 27.
    Hurtig, Kjell
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter2016In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 21, no 5, p. 339-350Article in journal (Refereed)
    Abstract [en]

    Comprehensive models of heat transfer require specification of the total amount of heat received by the workpiece. The objective of this work was to critically examine the use of a water-cooled stationary anode calorimeter to obtain both arc efficiency and total heat input into the workpiece. For simplicity and clarity, this last quantity is called the gross heat input. The effects of current, material type and water flow rate on the calorimeter performance were determined experimentally. Some measures for reducing errors in calorimetry were evaluated. Improvements were made to reduce heat losses from the top surface of the test coupon and boost heat removal from the opposite surface. A sensitivity test was conducted to estimate the effect of measurement inaccuracies. The results demonstrate the effectiveness of calorimetry for measuring gross heat input in arc welding.

  • 28.
    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.

  • 29.
    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

  • 30.
    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.

  • 31.
    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.

  • 32.
    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.

  • 33.
    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)
  • 34.
    Nilsson, Håkan
    et al.
    Chalmers University of Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Production Engineering.
    Sass-Tisovskaya, Margarita
    University West, Department of Engineering Science, Division of Production Engineering.
    Implementation of a 3D solver for electric arc welding, coupling fluid mechanics with electromagentics2011In: 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics. HEFAT2011: Mauritius, 11-13 july 2011, 2011, p. 614-620Conference paper (Refereed)
    Abstract [en]

    This paper describes the implementation of a 3D numerical solver for electric arc welding, where the fluid mechanics of the shielding gas is strongly influenced by the electromagnetic fields. The implementation is done in the OpenFOAM-1.6.x OpenSource Computational Fluid Dynamics (CFD) tool (www.openfoam.com). OpenFOAM is basically a general library of C++ classes for numerical simulation of continuum mechanic problems, but it is mainly used in CFD. The basics of high-level programming in OpenFOAM is described briefly, while the main components of the implementation done in the present work are described in high detail. The implementation is validated against an analytical solution of the electromagnetic field of an infinite electrically conducting rod, and against an experimental study of GTAW (Gas Tungsten Arc Welding). The numerical results agree very well with both the analytical and experimental results. A grid-dependency study has been made for the GTAW case, showing that the main features of the presented solutions are independent of the mesh size.

  • 35.
    Panwisawas, C.
    et al.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Sovani, Y.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Anderson, M.J.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Turner, R.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Palumbo, N. M.
    Rolls-Royce plc, Derby, UK.
    Saunders, B. C.
    Rolls-Royce plc, Derby, UK.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Brooks, J.W.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Basoalto, H.C.
    University of Birmingham, School of Metallurgy and Materials, UK.
    A Multi-scale Multi-physics Approach to Modelling of Additive Manufacturing in Nickel-based Superalloys2016In: Superalloys 2016: Proceedings of the 13th International Symposium on Superalloys / [ed] M. Hardy, E. Huron, U. Glatzel, B. Griffin, B. Lewis, C. Rae, V. Seetharaman och S. Tin, Minerals, Metals & Materials Society, 2016, p. 1021-1030Conference paper (Refereed)
    Abstract [en]

    A multi-scale, multi-physics modelling framework of selective laser melting (SLM) in the nickel-based superalloy IN718 is presented. Representative powder-bed particle distribution is simulated using the measured size distribution from experiment. Thermal fluid dynamics calculations are then used to predict melting behaviour, sub-surface morphology, and porosity development during a single pass scanning of the SLM process. The results suggest that the pores and uneven surface structure are exacerbated by increasing powder layer thicknesses. Predicted porosity volume fraction is up to 12% of the single track when 5 statistical powder distributions are simulated for each powder layer thickness. Processing-induced microstructure is predicted by linking cellular automatons – finite element calculations indicate further that the cooling rate is about 4400 o C/s and grain growth strongly follows the thermal gradient giving rise to a columnar grain morphology if homogeneous nucleation is assumed. Random texture is likely for as-fabricated SLM single pass with approximately 8 Pm and 6 Pm grain size for 20 Pm and 100 Pm powder layer thickness fabrication. Use has been made of the cooling history to predict more detailed microstructure using a γ" precipitation model. With the short time scale of solidification and rapid cooling, it becomes less likely that γ" precipitation will be observed in the condition investigated unless a prolonged hold at temperature is carried out. Future work on extension of the proposed multiscale modelling approach on microstructure predictions in SLM to mechanical properties will be discussed.

  • 36.
    Panwisawas, Chinnapat
    et al.
    University of Birmingham,School of Metallurgy and Materials, , Edgbaston, Birmingham B15 2TT, UK.
    Sovani, Yogesh
    University of Birmingham, School of Metallurgy and Materials, Edgbaston, Birmingham B15 2TT, UK.
    Turner, Richard P.
    University of Birmingham, School of Metallurgy and Materials, Edgbaston, Birmingham B15 2TT, UK.
    Brooks, Jeffery W.
    University of Birmingham, School of Metallurgy and Materials, Edgbaston, Birmingham B15 2TT, UK.
    Basoalto, Hector C.
    University of Birmingham, School of Metallurgy and Materials, Edgbaston, Birmingham B15 2TT, UK.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Modelling of thermal fluid dynamics for fusion welding2018In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 252, no February, p. 176-182Article in journal (Refereed)
    Abstract [en]

    A fluid dynamics approach to modelling of fusion welding in titanium alloys is proposed. The model considers the temporal and spatial evolution of liquid metal/gas interface to capture the transient physical effects during the heat source–material interaction of a fusion welding process. Melting and vaporisation have been considered through simulation of all interfacial phenomena such as surface tension, Marangoni force and recoil pressure. The evolution of the metallic (solid and liquid) and gaseous phases which are induced by the process enables the formation of the keyhole, keyhole dynamics, and the fully developed weld pool geometry. This enables the likelihood of fluid flow-induced porosity to be predicted. These features are all a function of process parameters and formulated as time-dependent phenomena. The proposed modelling framework can be utilised as a simulation tool to further develop understanding of defect formation such as weld-induced porosity for a particular fusion welding application. The modelling results are qualitatively compared with available experimental information.

  • 37.
    Stenbacka, Nils
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Mechanical Engineering. University West, Department of Engineering Science, Division of Welding Technology.
    Review of Arc Efficiency Values for Gas Tungsten Arc Welding2012Conference paper (Other academic)
    Abstract [en]

    The aim of this study was to review the literature that specifies arc efficiency values for gas tungsten arc welding (GTAW) and, if possible, propose a plausible value range. The literature review covered the years between 1955 and 2011, and showed that the arc efficiency values published lie in a wide range. Values between 0.36 and 0.90 were found for GTAW DCEN. Only a few studies covered DCEP and AC current welding. Specific information about the reproducibility of calorimetric studies was scarce (considering both random and systematic errors). A plausible arc efficiency range (95% confidence) for GTAW DCEN was estimated to be 0.73 – 0.82 with an average value of 0.78. The arc efficiency is lowered by longer arcs (increased arc gap). Reports describing the influence of arc current and travel speed, however, conflict. The GTAW process with DCEN is an efficient welding method.

  • 38.
    Svenungsson, Josefine
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Science and Mathematics, 971 87 Luleå, Sweden.
    Laser Welding Process: A  Review of Keyhole Welding Modelling2015In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, p. 182-191Article in journal (Refereed)
    Abstract [en]

    Laser welding is used in several industrial applications. It can be distinguished between conduction mode and keyhole mode welding, between pulsed wave and cw laser welding and between CO2-lasers with a wavelength of 10 μm and various laser types of about 1 μm wavelength. A deeper understanding of laser welding allows improving weld quality, process control and process efficiency. It requires a complementary combination of precise modelling and experimental investigations. The here presented review focuses on modelling of laser keyhole welding, for both wavelength regimes. First, the fundamentals of the laser welding process and its physics such as beam propagation, keyhole formation and melt pool dynamics are addressed. The main approaches for modeling energy transfer from laser beam to keyhole surface as well as fluid flow in the material are then discussed. The most relevant publications are systematically structured, particularly categorized with regard to the respective physical phenomena addressed. Finally some open questions are underlined.

1 - 38 of 38
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