Arc-cathode attachment in GMA welding

Abstract

A model for arc-cathode attachment in gas metal arc welding is presented. It considers the cathodic heating in the case of a non-refractory iron cathode, with the assumption of the lowering of the local plasma temperature, due to cold metal vapor. It takes the plasma bulk temperature as well as the cathode drop voltage as free parameters and it gives a maximum of heat flux and current density for a cathode surface temperature below boiling temperature. The applicability as a heat source description in a weld pool simulation has been shown, and the temperature field of the cathode was calculated, giving rise to heat flux and current density distributions, which differ significantly from the converntionally used axisymmetric Gaussian distribution. The maximum cathode surface temperature was lower than boiling temperature, which is in agreement with the observeration.

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

“…The presented model is based on the principle of evaporationdetermined arc cathode coupling (EDACC) as it was described in [11]. Therefore, the present work is concerned with the interface between the arc plasma and the weld pool, but does not attempt to describe either the arc plasma or the weld pool formation itself.…”

“…The model is described here following the algorithmic structure to allow for easy implementation in a GMAW weld pool process simulation, rather than for enabling following the physical logic, which was already described in [11]. This means also that constants have been evaluated and noted as numerical values, and all physical units have been omitted.…”

“…The model assumes an arc-pressure of 1.5 atm at the weld pool surface and, like the model presented in [11], only considers singly ionized iron states.…”

“…Following the reasoning described in [11], the local plasma temperature T Plasma, local is calculated as a mixture between the temperature of the metal vapor (assumed to be equal to the cathode surface temperature T W ) and the temperature of the plasma bulk T Plasma, bulk . However, while in [11] the mixture was assumed by equally weighted influence of plasma gas and evaporated metal, this assumption was a bit arbitrary, as the relevant length scales for ionization and the area of saturated metal vapor conditions were never really considered in detail. From the approach for the mixing of the plasma temperatures presented in [11] follows the presented approach (Eq.…”

“…It follows that there is a demand for a method to consider the cathode sheath processes more accurately. In [11], a model for the evaporation-determined arc-cathode coupling in GMAW (EDACC) was presented and its effects were investigated in [12]. In this model, the heat deposition from the plasma to the weld pool is realized by the arc-cathode interaction in the cathode layer and heat transfer by heat conduction plays only a minor role.…”