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A review of cathode-arc coupling modeling in GTAW
University West, Department of Engineering Science, Division of Production Engineering. (Welding)
University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering. (PTW Welding)ORCID iD: 0000-0003-2535-8132
2016 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, no 4, 821-835 p.Article in journal (Refereed) Published
Resource type
Text
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.

Place, publisher, year, edition, pages
2016. Vol. 60, no 4, 821-835 p.
Keyword [en]
GTA Welding, Cathodes, Mathematical models, Tungsten electrodes, Reviews, Simulating, Plasma, Heat flow
National Category
Applied Mechanics Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-9268DOI: 10.1007/s40194-016-0319-7ISI: 000385025900020ScopusID: 2-s2.0-84975709499OAI: oai:DiVA.org:hv-9268DiVA: diva2:919108
Note

First online: 21 March 2016

Available from: 2016-04-13 Created: 2016-03-30 Last updated: 2016-12-19Bibliographically approved
In thesis
1. Modelling of cathode-plasma interaction in short high-intensity electric arc: Application to Gas Tungsten Arc Welding
Open this publication in new window or tab >>Modelling of cathode-plasma interaction in short high-intensity electric arc: Application to Gas Tungsten Arc Welding
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology, 2016. 78 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, ISSN 0346-718X ; 4062
Keyword
Electric arc discharge, sheath, pre-sheath, Knudsen layer, doped refractory cathode, arc-cathode coupling, Gas Tungsten Arc simulation, OpenFOAM.
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9358 (URN)9789175973814 (ISBN)
Public defence
2016-06-10, VDL, Chalmers Tvärgata 4C, Chalmers, Göteborg, 10:00 (English)
Opponent
Supervisors
Available from: 2016-05-31 Created: 2016-05-31 Last updated: 2016-05-31Bibliographically approved

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