Abstract
This work presents modelling results concerning a tungsten inert gas (TIG) welding arc. The model provides a consistent description of the free burning arc, the arc attachment and the electrodes. Thermal and chemical non-equilibrium is considered in the whole arc area, and a detailed model of the cathode space-charge sheath is included. The mechanisms in the cathode pre-sheath are treated in the framework of a non-equilibrium approach which is based on a two-fluid description of electrons and heavy particles and a simplified plasma chemistry of argon. A consistent determination of the electrode fall voltages and temperature distributions is achieved. The model is applied to arcs in pure argon at currents up to 250 A, whereby welding of a workpiece made of mild steel with a fixed burner is considered. Arc voltages in the range from 12 to 17 V are obtained at 50 at 250 A, respectively. The space-charge sheath voltage is found to be about 7 V and almost independent of the current. The corresponding temperatures of the cathode tip are in the range from 3,000 K to about 3,800 K. The results obtained are in a good agreement with measurements.
Highlights
Tungsten inert gas (TIG) welding is widely used in metal working industry
The non-equilibrium arc model including the description of the cathode space-charge sheath is capable of predicting the arc voltage of a TIG process for different currents and electrode distances
The specific model allows the separate analysis of the leading voltage drops in the TIG process, in particular the voltage drops over the cathode space-charge sheath, the pre-sheath regions and the arc column
Summary
Tungsten inert gas (TIG) welding is widely used in metal working industry. It is a quite stable process suitable for. The transition region from the ionisation sheath to the arc column can be in addition affected by unequal electron and heavy particle temperature This fact can be considered in a proper way replacing the LTE arc model by a two-temperature plasma model. This option has been applied recently to the description of a TIG arc including the cathode fall and the tungsten cathode temperature [10]. The aim of this paper is the application of the model proposed in [11] to a more realistic TIG process and the determination of the total voltage drops as well as the tungsten cathode temperature distribution for different arc currents and electrode distances.
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