Abstract Scope |
Arc welding processes have been the subject of ongoing and extensive research studies due to their great technological importance. The main aims have been to understand the complex physical phenomena involved and optimize the processes to produce high quality and sound weld pieces. There have been attempts to understand and explain the physics involved in these complex phenomena present in the welding arc through simplified analytical solutions, numerical solutions and experimental measurements. Several models have been developed to predict the heat fluxes from the arc column to the weld pool. To the knowledge of the authors, no modeling work in the specialized literature describes and quantifies the importance of the heat transfer mechanisms in the arc column in a way that provides a simple picture of the physics of the arc column. In this work, a detailed analysis of the importance of the heat transfer mechanisms in the arc region is presented to understand the arc physics and to assess the relative contribution of each heat transfer mechanism from the arc to the weld pool.
A previously developed 2D steady-state mathematical model of a GTAW electric arc was used to analyze the relative importance of the main heat transfer mechanisms that heat or cool the plasma in the arc column. Building a map of the dominant mechanisms for heating and cooling the arc in each zone as well as their relative importance in terms of volumetric power was used to make this analysis possible. Identification of dominant mechanisms is based on the numerical results and the governing equations on a node-by-node basis.
The maps have features that provide insights into the arc physics, such as the dominant heat input and output mechanism in each zone of the arc, the relative intensity of the mechanisms, the relative importance of the dominant mechanisms, and the boundaries of the arc. It was found that the primary inputs of energy are due to convection near the anode and Joule heating near the cathode, while the main cooling mechanisms have a more complex structure that can be described in the map from cathode to the anode, composed of Thomson effect, convection, radiation and conduction. A systematic analysis was conducted to evaluate the effect of the arc current, arc length, and plasma gas on the map of dominant mechanisms. The main effect of current is on the intensities and extent of the zones of dominance of the mechanisms. The arc length does not significantly affect the map. The gas conmposition has the most significant effect on the zones of dominance of the mechanisms, in this case Ar and He were considered as gases. The heat transfer near the anode is governed by the momentum and thermal boundary layers due to the plasma jet, while the cathode heat transfer is dominated by the heat transfer mechanisms associated with current flow. The information provided may be used to perform simple energy balances in specific zones of the arc to gain a basic understanding of the physics in the electric arc. |