Dimensionless representation of the column characteristics and weld pool interactions for a DC argon arc

Abstract

The column characteristics and weld pool interactions for a DC argon arc in a GTAW configuration are represented by dimensionless correlations. Arc was described by a numerical model, considering currents between 200-300 A and arc lengths between 5-10 mm. The arc, defined as the loci of the 10,000 K isotherm, was found to display a parabolic shape; whose parameters are independent of current and arc length. Arc column temperature, velocity, and magnetic field are scaled with the width of the arc and a maximum that can also be predicted with a dimensionless approach. Arc-melt interactions include arc pressure, heat and current fluxes, and shear stress are also captured in dimensionless form. Scaling results compare well to numerical and experimental results reported.

General expressions for heat distribution, pressure, and current density in argon welding arcs

“…In previous work, a numerical model of an atmospheric pressure argon arc with a non-consumable DC-negative electrode was developed, solved numerically through the CFD code PHOENICS, and validated against experimental results and other numerical models by comparing the main arc characteristics and arc-weld pool interactions extensively [19], [20]. The main assumptions to model the arc column include considering Local Thermodynamic Equilibrium (LTE), axisymmetry, and optically transparent plasma in a steady state.…”

A numerical study of the effects of cathode geometry on tungsten inert gas type electric arcs

“…To quantify the variability in the stress and heat flux profiles at the API, two analytical functions are used to simplify the discussion. The functions are fit to the profiles of interest at the API similarly to Alvarez et al [8]. However, we use simpler (less parameters) analytical fits, motivated by the work in [16,17,24].…”

“…Current density manifests through the emission zones (spots) of an arc's cathode [1], therefore a change in spot area becomes a change in current density. The electron emission zone at a cathode can be the most influential boundary condition as it is the source of momentum for the arc [13,8]. A TIG arc is thus sensitive to the variations in cathode shape [7].…”

“…Moreover, due to the complexity of emission phenomena at cathode-plasma and anode-plasma interfaces (CPI, API), different approaches have been used when approximating current transport across or from the CPI. Authors like Hsu, Goodarzi, Alvarez impose cathode spots as boundary conditions (without incorporating a cathode into the computational domain), using experimentally estimated current densities [13,11,8]. Others use multi-species, non-LTE models to calculate current densities being emitted at the CPI [20,28].…”

“…The fitted variables are of use to engineers interested in replacing direct arc modelling with quasi-equivalent boundary conditions [24,16,17]. We also discuss, using the literature, the cathode spot as an arc boundary condition method, as seen in [13,11,8], as compared to our electrode-arc model, where cathode current densities are calculated through the interaction between the cathode and the arc at the CPI. Furthermore, we discuss the effect of the arc's hot core (zone of maximum temperature) on to the cathode.…”