MODELLING OF THE ARC IN ELECTRIC WELDINGARC-ELECTRODE COUPLING

Alireza Javidi

Supervisors:

Isabelle Choquet

Håkan Nilsson

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Outline

• Background and motivation

• Cathode layer model

• OpenFOAM implementation

• Results

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Weld with defect called weld metal porositySolidification cracks along the centre line of the weld

[www.twi-global.com]

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Modelling mainly covers:

• Residual stress

• Material macroscopic properties

• Weld pool behaviour

Heat source

Semi-empirical

Arc simulation

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Schematic sketch of sub-regions in GTAW

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Aim: to develop a self-consistent arc-electrode model that

• Suited to welding application

• Accounts for the relevant physics

• Satisfies the basic conservation requirements (i.e current and energy).

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Cathode layer

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Cathode layer model

Current densities at the cathode layer model

Thermal-field emission current density

Secondary emission current density

Ion current density

Back diffusion current density

TcTe

Us

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Cathode layer model

o Set of Saha equations

o Electric neutrality

o Dalton’s law

• Energy balance at the cathode/sheath interface

• Energy balance in the pre-sheath

• Current conservation

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• Set of Saha equations generalized by Van de Sanden

Number densities at the sheath/pre-sheath interface – equation system-1

• Dalton’s law

• Electric neutrality

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Energy balance in the pre-sheath layer:

Fluxes in the ionization layer

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Fluxes at the cathode/sheath interface

Energy balance at the sheath/cathode interface:

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Current conservation:

Single input value of the model

Jcath

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Numerical procedure

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D = 3.2 mm

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T_ownT_nbrV_ownV_nbrPj.ndelta_owndelta-nbr

Te,Tc,Us

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Thank you for your attention!