Wire melting phenomena in gas metal arc welding

Abstract

The wire melting rate in gas metal arc welding using constant voltage power supplies is well described by a parabolic model that considers the effects of electrical resistance and arc heating. However, tests performed with constant current power supplies indicate that the melting rate can deviate from this model when welding current is close to the globular–spray transition value. Although the causes of this anomaly have not yet been well established, most authors consider them to be related to variations in liquid metal temperature close to the metal transfer mode transition current. The present work evaluates the effect of welding parameters on the wire melting rate when a constant current power supply is used. A numerical model that considers the contribution of both Joule and arc heating was developed to calculate the temperature distribution in the wire and its melting rate. The model was used to assess the changes in either arc heating or metal vaporisation that might explain the melting irregularities. High speed cinematography was used to analyse metal transfer in the current range associated with the melting irregularities.