| 1. |
- Aryal, Pradip, et al.
(författare)
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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
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 194
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Proceedings of the World Congress on Mechanical, Chemical, and Material Engineering. - : Avestia Publishing. - 2369-8136. - 9781927877616
-
Konferensbidrag (refereegranskat)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. |
- Aryal, Pradip
(författare)
-
Gas Metal Arc Melt Pool Modelling : Effect of welding position and electromagnetic force mode
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas metal arc is a high-efficiency and widely used heat source for metal processing applied predominantly in welding and additive manufacturing. In this study, it was applied to welding. It offers high productivity, low production and investment cost, as well as suffers from some drawbacks such as humping or undercut when welding large parts that are curved and impose changing the orientation of the welding torch along the joint path. Deeper process understanding was therefore sought to mitigate these drawbacks. The difficulty is then the non-lineardependence of the process to the welding parameters and material properties. Besides, visual observation of this process is also difficult. For instance, the elevated temperature and the intense radiative emission from the electric arc, smoke, spatter, as well as the non-transparency of the processed alloy can hinder in-process observation or limit it. Process simulation provides a complementary means to reach process knowledge. It was thus the approach used in this study. For this, a thermo-fluid melt pool model that can predict melting and solidification, track free surface deformation, metal transfer, and coalescence with the melt pool was developed. Two main research questions were identified and addressed.The first one led to studying the effect of the substrate orientation during multilayer welding of a V-groove joint with INVAR and gas metal arc. It was foundthat the force balance in the melt pool changes significantly when the workpieceorientation is changed, resulting in distinct melt flow patterns, melt pool and bead geometries, and in some conditions defect initiation such as humping, undercut, and lack of fusion. As a result, multi-layer welding with flat substrate and downhill welding of a 20◦ inclined substrate are recommended with these process conditions. On the contrary, welding of a side inclined substrate and uphill welding of a 20◦ inclined substrate are not recommended. The second question gave rise to the comparative investigation of the three electromagnetic force models commonly used when modelling a melt pool produced by an electric arc. The underlying modelling assumptions were retrieved and investigated. It was found that each of these three models predicts a different melt flow pattern, different heat convection, melt pool shape, free surface oscillation, and interaction with the transferred metal drops, and thus result in different bead geometry. All these models can be adjusted to predict the penetration depth, however, only the most complete of them is recommended for developing a predictive melt pool model. For this, it is proposed as a future work to improve this model through predicting an electromagnetic force that takes also into account the local deformation of the free surface.
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| 4. |
- Aryal, Pradip, et al.
(författare)
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Melt pool electromagnetic force model extended to account for free surface deformation : Application to gas metal arc
- 2024
-
Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310 .- 1879-2189. ; 221, s. 124987-124987
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Tidskriftsartikel (refereegranskat)abstract
- Computational fluid dynamics models with free surface tracking intended to simulate the melt pool produced by an electric arc usually model the electromagnetic force ignoring the deformation of the free surface. However, with an arc heat source, the electromagnetic force is known to be among the leading-order forces, especially at high currents. In addition, the free surface can undergo significant deformations, especially in the presence of metal transfer. In the present study, a generalization of the electromagnetic force model that accounts for the deformation of the free surface is therefore proposed. Test cases with a pulsed gas-metal arc that transfers one metal drop per pulse were investigated experimentally at three different travel speeds to provide validation data. The cases were simulated with both the proposed and the earlier model to assess the influence of the new developments. The results showed that, in the regions where both models determine the force, the discrepancy between the models’ results can reach up to an order of magnitude. Especially, the earlier model overestimates the electromagnetic force deep into the melt pool. On the other hand, it neglects it in the liquid metal that is located at an elevation above the original upper surface of the workpiece, while the proposed model showed that in this area the intensity of the electromagnetic force is the largest. These significant discrepancies result in non-negligible differences in the predicted melt pool thermal flow and geometry. Especially, the propose dextended model provides an improved prediction of the fingertip-shaped fusion boundary.
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| 5. |
- Aryal, Pradip
(författare)
-
Metal fusion using pulsed GasMetal Arc : Melt pool modellingand CFD simulation
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pulsed gas metal arc is a highly efficient technique used in manufacturing processes like welding and additive manufacturing. It offers high productivity and cost benefits but it is also prone to defect formation when process parameters are not properly controlled and optimized. A deeper process understanding can support achieving improved process control and mitigate these potential drawbacks. Nevertheless, there are still several challenges. For instance, the correlation between the input and output process parameters is non-linear and complex due to the multi-physics nature of the process. In addition, the elevated temperature and the intense radiative emission from the arc, along with the smoke, and the non-transparency of metal, make in-process observation challenging. Modelling and simulation offer a complementary approach to gain a deeper process understanding. In this study, a thermo- and fluid dynamics model was developed, focusing on the melt pool and metal deposition, while simplifying the arc to boundary conditions (decoupled approach). This model incorporates various forces and phenomena such as thermocapillary and electromagnetic forces, melting and solidification, and tracking of surface deformation and droplet coalescence.In the first part of the thesis, the developed model was applied to investigate the effect of workpiece orientations on the melt pool dynamics and reinforced bead geometry in multi-layer gas metal arc welding of a V-groove joint. The comparison of the predicted fusion zone with macrographs obtained from the experiments showed good qualitative agreement. It was found that the force balance in the melt pool changes significantly when changing the workpiece orientation by as little as 20◦ relative to the flat position. This results in distinct melt flow patterns, melt pool shapes, bead geometries, and in some cases, defect formation such as humping, undercut, and insufficient fusion. It was concluded that to avoid these defects a lower angle range is necessary for multilayer welding with the uphill orientation and side inclination.The second part of the thesis focused on analyzing different variants of the model for the electromagnetic force with a decoupled approach. Three commonly used models were compared: (1) the analytical models proposed by Kou and Sun inintegral form, (2) by Tsao and Wu in algebraic form, and (3) the partial differential equations governing the electric and magnetic fields. The comparative investigation was supported by experimental tests that also provided estimates of unknown model parameters and validation data. It was found that the distinct assumptions on which these models rely are not all justified. They resulted inpredicting different melt flow patterns and amplitude of the free surface oscillations, as well as different melt pool shapes and bead geometries. Model (3) is recommended to advance to a predictive melt pool model and was subsequentlyused in the remaining work of the thesis.Furthermore, the literature shows that modeling the effect of pulsed arc on the melt pool using a decoupled approach involves various simplifications. Arc pulsation affects energy and force balance in the melt pool through arc heat flux, arc pressure, and electromagnetic force. A systematic investigation of model variants considering pulsing was conducted using previously documented experimental test cases. The results showed that the influence of arc pressure was insignificant in those cases. However, model variants simplifying arc pulsing to a time-averaged effect underestimated the amplitude of the Marangoni flow and downward flow compared to a more comprehensive approach that considered the time dependence of arc pulsation. Thus, it is recommended to use a meltpool model that accounts for the time-dependent arc pulsation, which was also subsequently utilized in the remaining work of the thesis.The electromagnetic force models discussed earlier assume a stationary free surface when computing the electromagnetic force. However, this force is often at leading order in the vicinity of the arc. In the same region, the metal drop transfer leads to a periodic deformation of the melt pool free surface. In the final part of the thesis, the model was extended to account for free surface deformation when computing the electromagnetic force. This extension was applied to experimental test cases, and a comparison was made with simulation results obtained using the stationary electromagnetic force model. Significant differences in the results were observed, particularly in predicting the experimentally observed fingertip-shaped fusion zone geometry. The proposed improvement in the electromagnetic force model provided better predictions in this regard.
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| 6. |
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| 7. |
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| 8. |
- Beaubert, Francois, et al.
(författare)
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Design of a device to induce swirling flow in pipes : A rational approach
- 2015
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Ingår i: Comptes rendus. Mecanique. - : Elsevier BV. - 1631-0721 .- 1873-7234. ; 343:1, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Beaubert, F., et al.
(författare)
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Fundamental mode of freely decaying laminar swirling flows
- 2016
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Ingår i: Applied Mathematical Modelling. - : Elsevier BV. - 0307-904X .- 1872-8480. ; 40:13-14, s. 6218-6233
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Chazelas, Christophe, et al.
(författare)
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Main issues for a fully predictive plasma spray torch model and numerical considerations
- 2017
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Ingår i: Plasma chemistry and plasma processing. - : Springer Science and Business Media LLC. - 0272-4324 .- 1572-8986. ; 37:3, s. 627-651
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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A hierarchy of diffusion models for partially ionized plasmas
- 2007
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Ingår i: Discrete and continuous dynamical systems. Series B. - 1531-3492 .- 1553-524X. ; 8:2, s. 735-772
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Tidskriftsartikel (refereegranskat)abstract
- Partially ionized plasmas corresponding to different ionization degrees are derived and connected one with each other by the diffusion approximation methodology. These plasmas are the following electrical discharges:a thermal arc discharge, glow discharges in local thermodynamic equilibrium -LTE- and in non-LTE, and a non-LTE glow discharge interacting with an electron beam (or flow)
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| 12. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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A strong ionization model in plasma physics
- 2009
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Ingår i: Mathematical and Computer Modelling. - : Elsevier BV. - 0895-7177. ; 49:1-2, s. 88-113
-
Tidskriftsartikel (refereegranskat)
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| 13. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Clogging and lump formation during atmospheric plasma spraying with powder injection downstream the plasma gun
- 2007
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 16:4, s. 512-523
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
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| 15. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Electric welding arc modeling with the three-dimensional solver OpenFOAM : A comparison of different electromagnetic models
- 2011
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Ingår i: 64 th Annual Assembly and International Conference of International Institute of Welding, 64th IWW. ; , s. 212-1189-11-1-212-1189-11-16
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 16. |
- Choquet, Isabelle, 1965-
(författare)
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Gas tungsten arc models including the physics of the cathode layer : remaining issues
- 2018
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Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 62:1, s. 177-196
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 17. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Hydrodynamic limit for an arc discharge at atmospheric pressure
- 2005
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Ingår i: Journal of statistical physics. - : Springer Science and Business Media LLC. - 0022-4715 .- 1572-9613. ; 119:1-2, s. 197-239
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 18. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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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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Ingår i: ASM Proceedings of the International Conference: Trends in Welding Research 2013. - Chicago, IL : ASM International. - 9781627089982 ; , s. 876-885
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Konferensbidrag (refereegranskat)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. Copyright © 2013 ASM International® All rights reserved.
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| 19. |
- Choquet, Isabelle, 1965-, et al.
(författare)
-
Modeling and simulation of a heat source in electric arc welding
- 2011
-
Ingår i: Proceedings from the 4th Swedish Production Symposium, Lund, Sweden. ; , s. 202-211, s. 201-211
-
Konferensbidrag (refereegranskat)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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| 20. |
- Choquet, Isabelle, 1965-, et al.
(författare)
-
New powder port holder geometry to avoid lump formation in APS
- 2005
-
Ingår i: 17th international symposium on plasma chemistry (ISPC 17). ; , s. OP7. 1-6
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 21. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Non equilibrium ionization in magnetized two-temperature thermal plasma
- 2011
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Ingår i: Kinetic and Related Models. - : American Institute of Mathematical Sciences (AIMS). - 1937-5093 .- 1937-5077. ; 4:3, s. 669-700
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Choquet, Isabelle, 1965-
(författare)
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Nozzle exit geometry and lump formation in atmospheric plasma spraying
- 2005
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Ingår i: International Thermal Spray Conference. - : ASM International. ; , s. 259-264
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 23. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Numerical simulation of Ar-x%CO2 shielding gas and its effect on an electric welding arc
- 2011
-
Ingår i: IIW Commission XII / SG 212 Intermediate meeting, University West, Trollhättan, Sweden, 21 - 23 March 2011, IIW Doc. XII-2017-11. ; , s. 1-12
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 24. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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On the choice of electromagnetic model for shorthigh-intensity arcs, applied to welding
- 2012
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 45:20, s. 205203-
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Tidskriftsartikel (refereegranskat)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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| 25. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Process modeling of powder bed and directed energy deposition
- 2023. - 1.
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 518-611
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Bokkapitel (refereegranskat)abstract
- Metal additive manufacturing (AM) is used to build and repair metal parts with heat input from a high-power beam (laser or electron beam) or electric arc (gas metal, gas tungsten, or gas plasma arc) and metal deposited layer by layer from powder or wire feedstock. This multiscale and multiphysics process is difficult to directly observe. It's modeling thus contributes to gaining process understanding. It can also support process parameter selection, process control, path planning, modeling and analysis of microstructure, distortion, and residual stress formed during metal AM. The sections of this chapter address first the electron beam, laser beam, and electric arc heat sources including their interaction with metal. Next, it covers process modeling with the thermal and thermo-fluid approaches and metal provided in the form of either powder or wire feedstock. Each of these sections includes a description of the physics taking place, the existing modeling approaches, the related assumptions and framework of application, open questions, as well as examples of knowledge the models provide access to.
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| 26. |
- Gaudiuso, Caterina, et al.
(författare)
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Incubation during laser ablation with bursts of femtosecond pulses with picosecond delays
- 2018
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Ingår i: Optics Express. - 1094-4087. ; 26:4, s. 3801-3813
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 27. |
- Gaudiuso, Caterina, et al.
(författare)
-
Incubation effect in burst mode fs-laser ablation of stainless steel samples
- 2018
-
Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 10520
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 28. |
- Hosseini, Vahid, 1987-, et al.
(författare)
-
A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients
- 2017
-
Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 121:May, s. 11-23
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 29. |
- Hurtig, Kjell, 1960-, et al.
(författare)
-
A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter
- 2016
-
Ingår i: Science and technology of welding and joining. - : Informa UK Limited. - 1362-1718 .- 1743-2936. ; 21:5, s. 339-350
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 30. |
- Javidi Shirvan, Alireza, et al.
(författare)
-
A review of cathode-arc coupling modeling in GTAW
- 2016
-
Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 60:4, s. 821-835
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 31. |
- Javidi-Shirvan, Alireza, 1978, et al.
(författare)
-
Coupling boundary condition for high-intensity electric arc attached on a non-homogeneous refractory cathode
- 2018
-
Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 222, s. 31-45
-
Tidskriftsartikel (refereegranskat)abstract
- The boundary coupling high-intensity electric arc and refractory cathode is characterized by three sub-layers: the cathode sheath, the Knudsen layer and the pre-sheath. A self-consistent coupling boundary condition accounting for these three sub-layers is presented; its novel property is to take into account a non-uniform distribution of electron emitters on the surface of the refractory cathode. This non-uniformity is due to cathode non-homogeneity induced by arcing. The computational model is applied to a one-dimensional test case to evaluate the validity of different modeling assumptions. It is also applied coupling a thoriated tungsten cathode 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 results show that the non-uniformity of the electron emitters’ distribution has a significant effect on the calculated properties. It leads to good agreement with the cathode surface temperature, and with the plasma temperature in the hottest region. Some differences are observed in colder plasma regions, where deviation from local thermal equilibrium is known to occur.
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| 32. |
- Javidi Shirvan, Alireza, et al.
(författare)
-
Effect of cathode model on arc attachment for short high-intensity arc on a refractory cathode
- 2016
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 49:3 November 2016, s. 1-17
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 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
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| 33. |
- Javidi Shirvan, Alireza, et al.
(författare)
-
Numerical modelling of shielding gas flow and heat transfer in laser welding process
- 2012
-
Ingår i: Proceedings of the 5th International Swedish Production Symposium, SPS12. - Linköping. - 9789175197524 ; , s. 1-7
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 34. |
- Mi, Yongcui, 1986-, et al.
(författare)
-
Conduction mode laser welding with beam shaping using a deformable mirror
- 2022
-
Ingår i: Optics and Laser Technology. - : Elsevier Ltd. - 0030-3992 .- 1879-2545. ; 148
-
Tidskriftsartikel (refereegranskat)abstract
- This study explores the possibility of tailoring the fusion zone in conduction mode laser welding using a deformable mirror for beam shaping of multi-kilowatt continuous wave laser sources. Three power density distributions were shaped and used in bead on plate welding of Ti64 plates in conduction mode at three travel speeds. The effect on melt pool free surface geometry, cross section, microstructure and hardness profiles was measured and studied. It is shown that the geometry of the melt pool can be modified using a deformable mirror. A narrower and longer melt pool or a wider, shorter and shallower one were indeed obtained forming Gaussian-elliptical power density distributions oriented along and transverse to the travel direction, respectively. The latter distribution could be a favourable option for laser beam additive manufacturing as it could improve process efficiency while reducing remelting of the previous layer. This system has also a promising potential for adaptive process control since it could change fundamentally the beam shape at a rate faster than 10 ms.
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| 35. |
- Mi, Yongcui, 1986-
(författare)
-
Novel beam shaping and computer vision methods for laser beam welding
- 2021
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser beam welding has been widely applied in different industrial sectors due to its unique advantages. However, there are still challenges, such as beam positioning in T-joint welding, and gap bridging in butt joint welding,especially in the case of varying gap width along a joint. It is expected that enabling more advanced control to a welding system, and obtaining more in-depth process knowledge could help to solve these issues. The aim of this work is to address such welding issues by a laser beam shaping technology using a novel deformable mirror together with computer vision methods and also to increase knowledge about the benefits and limitations with this approach.Beam shaping in this work was realized by a novel deformable mirror system integrated into an industrial processing optics. Together with a wave front sensor, a controlled adaptive beam shaping system was formed with a response time of 10 ms. The processes were monitored by a coaxial camera with selected filters and passive or active illumination. Conduction mode autogenous bead-on-plate welding and butt joint welding experiments have been used to understand the effect of beam shaping on the melt pool geometry. Circular Gaussian, and elliptical Gaussian shapes elongated transverse to and along the welding direction were studied. In-process melt pool images and cross section micrographs of the weld seams/beads were analyzed. The results showed that the melt pool geometry can be significantly modified by beam shaping using the deformable mirror. T-joint welding with different beam offset deviations relative to the center of the joint line was conducted to study the potential of using machine learning to track the process state. The results showed that machine learning can reach sufficient detection and estimation performance, which could also be used for on-line control. In addition, in-process and multidimensional data were accurately acquired using computer vision methods. These data reveal weaknesses of current thermo-fluid simulation model, which in turn can help to better understand and control laser beam welding. The obtained results in this work shows a huge potential in using the proposed methods to solve relevant challenges in laser beam welding.
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| 36. |
- Nilsson, Håkan, 1971, et al.
(författare)
-
Implementation of a 3D solver for electric arc welding, coupling fluid mechanics with electromagentics
- 2011
-
Ingår i: 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics. HEFAT2011. ; , s. 614-620
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 37. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-, et al.
(författare)
-
CFD-Based Feasibility Study of Laser-Directed Energy Deposition With a Metal Wire for On-Orbit Manufacturing
- 2022
-
Ingår i: Frontiers in Space Technologies. - : Frontiers Media S.A.. - 2673-5075. ; 3, s. 1-13
-
Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing of parts on-site in space requires investigating the feasibility ofadapting to zero-gravity and near-vacuum conditions, a technology applied today on Earthat standard conditions. While a few studies have been conducted for powder bed fusion, afeasibility study remains to be explored for direct energy deposition using a laser beam anda metal wire. This is the purpose of this study, which is conducted using a modelingapproach based on computational fluid dynamics. The simulation model developedincludes melting, re-solidification, vaporization, prediction of beam energy absorptionas a function of the local surface temperature and curvature, ray tracing, tracking of freesurface deformation and metal transfer, and wire-resistive heating. The study is carried outby starting from process parameters suited for stable on-Earth metal deposition. Theseconditions were also studied experimentally to validate the simulation model, leading tosatisfactorily results. A total of three other test cases with ambient pressure lowered downto near-vacuum and/or gravitation down to zero are investigated. It is found that,compared to on-Earth conditions, in-space conditions can induce vaporization of themetal alloy that is large enough to result in a curvature of the melt pool free surface but toosmall to lead to the formation of a keyhole. The in-space conditions can also modify theforce balance at the liquid melt bridge between the wire and the melt pool, leading to smallchanges in the curvature and temperature field at the free surface of the wire tip. Among theobserved consequences are a small increase of the melt pool length and a small elevationof the bead height. More importantly, for process control, changing to in-space conditionsmight also affect the stability of the process, which could be assessed through the width ofthe liquid metal bridge. However, by using appropriate process control to maintain acontinuous liquid metal bridge, it is concluded that direct energy deposition of metal usinga laser and a wire could be used for manufacturing metal parts in-space in a temperedatmosphere.
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| 38. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-, et al.
(författare)
-
Effect of shaped laser beam profiles on melt flow dynamics in conduction mode welding
- 2021
-
Ingår i: International journal of thermal sciences. - : Elsevier BV. - 1290-0729 .- 1778-4166. ; 166, s. 1-15
-
Tidskriftsartikel (refereegranskat)abstract
- A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusion welding on melt thermal flow. Three beam shapes are studied at several welding travel speeds: a reference Gaussian profile and its elliptic elongations along and transverse to the welding travel direction. It is found that these beam shapes change not only the intensity and direction of the melt thermocapillary flow but also the flow pattern. For instance, and contrary to the other profiles, the beam shape elongated along the welding travel direction generates melt front vortices that assist metal pre-heating. It can result in deeper penetration, larger melt volume, and lower amount of thermal energy diffused into the heat affected zone. The simple elongation of a beam profile has thus a non-linear effect on the melt flow and in turn on the seam geometry as well as the temperature gradients in the heat affected zone.
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| 39. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-, et al.
(författare)
-
Influence of Laser Beam Shaping on Melt Pool Thermocapillary Flow
- 2020
-
Ingår i: Proceedings of the 6th World Congress on Mechanical, Chemical, and Material Engineering (MCM'20) Prague, Czech Republic Virtual Conference – August, 2020. - : Avestia Publishing.
-
Konferensbidrag (refereegranskat)abstract
- The effect of different shapes of laser beam power density distribution was investigated numerically with respect to the thermo-hydrodynamics of the melt pool during welding. The process addressed is conduction mode bead on plate welding of the Titanium alloy Ti-6Al-4V. A new solver based on the volume of fluid method to track the deformation of the melt free surface was developed in the OpenFOAM software. Experiments were conducted for the purpose of validating the model. In addition to the traditional cross-cut images of the weld bead, top view images of the melt pool were analysed to perform the validation along the 3-space dimensions. A good agreement between numerical predictions and experimental measurements was obtained, thus promising aconfident utilization of this simulation model when investigating the influence of beam shapes on the resulting weld seam. The effectof three different beam shapes on the melt pool velocity flow, temperature fields, and melt geometry were studied. It was found that the melt pool size was largest for an elliptical power density distribution with the major axis along the welding direction. The results also showed that the laser beam with Gaussian power density distribution resulted in the deepest penetration.
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| 40. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-, et al.
(författare)
-
Influence of laser-wire interaction on heat and metal transfer in directed energy deposition
- 2023
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 205
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, laser metal fusion with feedstock wire is addressed. We investigated how various process parameters affect the fraction of beam energy that is absorbed by the wire and the workpiece and the metal transfer from the feedstock wire to the melt pool. To perform this research, a thermo-fluid dynamic model with tracking of free surface deformation was developed to include the feeding of a solid wire and predict its melting. The fraction of beam energy absorbed by the metal was modeled as a function of local surface curvature and temperature, accounting for multiple Fresnel reflections and absorptions. The model was applied to Titanium alloy (Ti-6Al-4V) with a 1.07 μm laser and a process in conduction mode. Experiments at various wire feeding rates were conducted to evaluate the model’s ability to predict the process and a good agreement was obtained. The different parameters studied were the beam angular position, the wire angular position, the wire feed rate, and the beam-wire offset. The analysis of the simulation results gave a detailed physical understanding of the laser energy use. It highlighted that thermocapillary and Rayleigh-Plateau instabilities can contribute to the transition from continuous to drop metal transfer mode. Damping these instabilities might thus allow using a wider process window.
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| 41. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-
(författare)
-
Investigation of Melt Pool Thermo-hydrodynamic Behaviour inLaser Beam Welding ofTi-6Al-4V through Numerical Simulation
- 2021
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser is an efficient and widely used heat source in metal processing suchas welding and additive manufacturing. It has some great advantages compared to the other conventional heat sources like electron beam and arc namely: ability of handling complicated joint geometries and producing large components. Laser beam welding encompasses many complex physical phenomena such asheat transfer, metal melting, flow and solidification, free surface deformation, evaporation and possibly vaporization. The aim of this research work istwo-fold: gain deeper process understanding and improve the model reliability. Deeper process understanding is sought on the effect of beam shaping on themelt pool. To achieve improved model reliability, a good support consists in using qualitative experimental data representing the process. Thus, 3D validation of the melt pool geometry is performed while it was usually 2D inprevious research works. Furthermore, a new calculation procedure for laser absorption is introduced. To conduct this research work, a Computational Fluid Dynamics approach is used. A solver, capable of tracking the deformation of the melt free surface, is developed in OpenFOAM. Concerning beam shaping, it is found that not only the melt pool size as previously known but also the melt flow pattern is modified through elongating the beam shape.This last result could not be revealed by former studies as the non-transparent media hinders optical observation. New in-process quantitative measurements performed by a project partner are used to test the model. Weaknesses of the former absorptivity models are highlighted, as well as the limitations of the proposed model. Finally, the results show that the proposed absorptivity model function of local surface conditions leads to much better agreement with experimental results compared to the former constant absorptivity model. The maximum discrepancy compared to the experimental measurement, which is observed for the melt pool depth, can indeed be reduced to about 10%.
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| 42. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-
(författare)
-
Laser metal fusion and deposition using wire feedstock : Process modelling and CFD simulation
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser metal fusion is widely used in production technology to manufacture parts, as in welding, cladding, and additive manufacturing. In this study, conduction mode laser metal fusion is applied without and with metal deposition from a wire feedstock. This manufacturing process encompasses various physical phenomena that are coupled, such as the interaction of anelectro-magnetic wave with the material, phase changes, thermal fluid dynamics, and free surface deformation, which make it complicated to comprehend.Deeper process knowledge is thus a key to its improvement. Yet, metal is a non-transparent media, which limits experimental observation of this process.A modelling approach that describes this multi-physics problem paying special attention to convective phenomena was used in this thesis with a two-fold aim:1) to improve the model reliability,2) to gain a deeper understandingof the metal fusion and deposition process.In the first part of this research, metal fusion without wire was addressed. Different beam power density distributions (beam shapes) were investigated. Their effect on the melt pool geometry, which was known from previous experimental studies, could be predicted. Furthermore, as the simulations give access to the melt flow, it could be established that the flow pattern is modified by elongating the beam shape. In addition, a new calculation procedure was introduced to predict the fraction of laser beam energy absorbed by the metal. To validate the model, the predicted melt pool geometry was evaluated through comparison with experimental measurements. The results showed that the proposed absorptivity model that is a function of local surface conditions lead to good agreement with experimental results, with a maximum discrepancy for the melt pool depth of about 10%.In the second part, the model was applied to study the fusion process with metal transfer from a wire feedstock without and with resistive heating of the filler wire. It was shown that the multipler eflections of beam rays could be ignored at a low laser beam angle whereas with increasing the beam angle the effect became more considerable. It was also found that the laser absorptivity varied up to 50% within the projected laser spot area. The effect of different process parameters such as depositing rate and angle, laser beam angle, position of the wire relative to the beam (offset), and ambient conditions on the metal transfer, thermal flow field, andstability of the process were studied.The results showed that three different metal transfer modes occurred depending on the offset value. Applying resistive heating on the filler wire decreased the absorptivity. However, this decrease was compensated by the resistive heating, resulting in an increase of the volume of liquid metal. Resistive heating made the melt pool wider due to the augmented role of the thermocapillary force and also the change in flow direction because of the modified position of the melted wire front.Applying the model at near-vacuum and no gravity conditions, it was obtained that directed energy deposition of metal with laser and wire could be used for manufacturing metal parts in space. However, the process window could need some adjustment as in-space conditions result in some narrowing of the liquid bridge between wire and workpiece compared to on-Earth.
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| 43. |
- Noori Rahim Abadi, Seyyed Mohammad Ali, 1985-, et al.
(författare)
-
Modelling of beam energy absorbed locally in conduction mode laser metal fusion
- 2021
-
Ingår i: Journal of physics. D, Applied physics. - Bristol : IOP Publishing. - 0022-3727 .- 1361-6463. ; 55:2
-
Tidskriftsartikel (refereegranskat)abstract
- Fluid dynamics models for laser material processing with metal fusion in conduction mode generally assume a constant absorptivity. This parameter is known to govern the process. However, it used to be pre-set by extrapolating absorptance measurements made at different conditions or adjusted to reproduce experimental bead shapes. In this study a new approach isd eveloped. It consists in predicting the absorptance as a function of local surface conditions, including the surface temperature. The proposed absorptance model is applied to the metal alloyTi-6Al-4V. It is found that the absorptance of this alloy changes with surface temperature over awide range of beam incidence angles. Thermo-fluid simulations with tracking of the free-surface deformation are performed for conduction mode beam welding test cases with a Yb fibre laser and different travel speeds. It is found that the absorptivity coefficient commonly used for this process clearly underestimates the absorptance and the melt pool geometry predicted for the process conditions of this study. The computational results are also compared against experimental results and good quantitative agreement of the melt pool depth, width, length, free surface contour geometry, and the curvature of the end depression left afterre-solidification at the laser switch-off location is obtained. The results show that the absorptance field predicted depends on the melt pool development stage, on the spatial location within the beam spot, and on the process conditions.
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| 44. |
- Panwisawas, C., et al.
(författare)
-
A Multi-scale Multi-physics Approach to Modelling of Additive Manufacturing in Nickel-based Superalloys
- 2016
-
Ingår i: Superalloys 2016. - : Minerals, Metals & Materials Society. - 9781118996669 ; , s. 1021-1030
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 45. |
- Panwisawas, Chinnapat, et al.
(författare)
-
Modelling of thermal fluid dynamics for fusion welding
- 2018
-
Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 252:February, s. 176-182
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 46. |
- Stenbacka, Nils, 1947-, et al.
(författare)
-
Review of Arc Efficiency Values for Gas Tungsten Arc Welding
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 47. |
- Svenungsson, Josefine, 1984-, et al.
(författare)
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Laser Welding Process : A Review of Keyhole Welding Modelling
- 2015
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 78, s. 182-191
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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