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Modelling of electrode-arc coupling in electric arc welding
University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering. (PTW)ORCID iD: 0000-0002-7897-621X
University West, Department of Engineering Science, Division of Manufacturing Processes. (PTW)ORCID iD: 0000-0003-2535-8132
Chalmers University of Technology.
2014 (English)In: Proceedings of The 6th International Swedish Production Symposium 201416-18 September 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, 1-8 p.Conference 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.

Place, publisher, year, edition, pages
2014. 1-8 p.
Keyword [en]
thermal plasma, arc welding, electrode layer, sheath, electrode surface temperature, numerical simulation, OpenFOAM.
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-6622ISBN: 978-91-980974-1-2 (print)OAI: oai:DiVA.org:hv-6622DiVA: diva2:745929
Conference
The 6th International Swedish Production Symposium 201416-18 September 2014
Projects
SUMMAN
Funder
Knowledge Foundation
Available from: 2014-09-11 Created: 2014-09-11 Last updated: 2016-05-31Bibliographically 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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Citation style
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