Simplified surface heat source distribution for GMAW process simulation based on the EDACC principle

Abstract

A simplified surface heat source for gas metal arc welding (GMAW) process simulation based on the principle of evaporation determined arc cathode coupling (EDACC) is presented. It allows for a simple implementation in any GMAW weld pool simulation and is dependent on the width of the arc, as well as the weld pool surface temperature, but it can also be applied with the temperature and iron vapor density of the plasma instead of the width of the arc, if available. While it is considered separately from the droplets, it gives the heat flux as well as the current density distribution onto the weld pool surface, which are in general not axis-symmetric. The heat source distribution is normalized and multiplied to the value of any total heat and total current and it allows to calibrate for the maximum weld pool surface temperature. For the ionization and evaporation, only iron atoms are considered, and the shielding gas is assumed as argon. The result is given in graphical form as well as in the form of easy to implement functions for a reasonable range.

Validation of evaporation-determined model of arc-cathode coupling in the peak current phase in pulsed GMA welding

“…The latter is considered as a linear mixing of the temperature T s of the evaporated atoms from the cathode and the temperature of the plasma bulk T plasma,bulk with the density n plasma,bulk . However, to match the real temperatures, this relationship can be extended with a weighting factor ω (T s ) to account for a non-linear influence of the metal vapor from the cathode on the ionization degree of the plasma close to the cathode, see [5].…”

“…Yet, the ion flux still needs to be strong enough to allow for the observed current transfer. The model presented in [13] and [9] can meet these conditions by introduction of the empirical weighting factor as defined in equation (5). Given that the EDACC model still relies on a number of assumptions, like local thermodynamic equilibrium (LTE) for the application of the Saha equation, or the simplified approach of determining the local plasma temperature T plasma, local in terms of a simple mixture, the introduction of the empirical weighting factor can be understood to correct for the insufficiencies of these assumptions.…”

“…However, approaches that attempt to take into account the underlying physics of the cathode layer, i.e. [4] or [5] are not yet well established and investigated. One of the reasons is that the most prominent approaches for the consideration of the plasma-cathode interaction tend to predict cathode surface temperatures that are considerably higher than boiling temperature >3144 K [6][7][8].…”