Anomalias na velocidade de fusão do eletrodo na soldagem GMAW

Abstract

Wire melting rate in GMA welding with constant voltage power suplies is well described by a parabolic model that links the melting of the wire with electrical resistance and arc heating. However, tests performed with constant current power supplies indicate that the melting rate can deviate from the values predicted by this model when welding current is close to the globular to spray transition. Although the causes of these irregularities have not been well established yet, most authors consider them to be related to variations in liquid metal temperature close to the metal transfer transition current. This thesis evaluates the effect of welding parameters on the wire melting rate obtained in trials using a constant current power supply. A numerical model that consideres the contribution of both Joule and arc heating and includes the effect of temperature on the physical properties of the wire was developed to calculate the temperature distribution in the wire and its meltingrate. The experimental results were used with the model to assess the changes in either arc heating or metal vaporisation capable to explain the melting irregularities. High speed cinematography was used to analyse metal transfer in the current range associated with the melting irregularities.