Study of the wire resistance in gas metal arc welding

The main aim of this investigation is to study the temperature and electrical resistance of the wire during gas metal arc welding (GMAW), because the wire heating contributes to a considerable extent to the power balance of the welding processes. As a reference, a typical pulsed GMAW process of mild steel with fixed wire feed speed of 4 m min(-1) but varying free wire length and varying pulse current has been investigated. Three approaches have been applied for comparison: firstly, the surface temperature of the solid and molten wire parts has been measured with an infrared camera and a two-colour pyrometer with high-speed recording, respectively, and the wire resistance has been determined based on wire geometry and temperature dependent conductivity. Secondly, the resistance of the solid wire and the wire contact in the contact tube has been measured by an electrical probe. Thirdly, short circuit events together with surface temperature determination have been used to estimate the wire resistance. In addition, the temperature dependent conductivity of the corresponding wires has been measured systematically in a specific heating setup. Main results are a wire temperature exponentially decreasing with the distance from the wire tip and almost independent of the pulse current. The overall resistance of the wire part in the current path of the process including the contact tube scales mainly with the free wire length and reaches 13 m Omega in our example for 15 mm free wire length.