Study of the arc voltage in gas metal arc welding

In this paper, the voltage drop in pulsed gas metal arc welding (GMAW) is studied, focussing on the contributions of the different sections of wire and arc along the current path and their dependence on arc length and current. A typical pulsed GMAW process of mild steel in the one drop per pulse modus is considered as a reference. Voltage and current have been measured in experiments with fixed wire feed speed for varying arc length and free wire length. The temporally changing geometry of the arc and the molten wire parts has been studied carefully by high-speed imaging and image processing. In particular, the shielding gas and the metal vapour dominated parts of the arc have been captured simultaneously, and conclusions on the length of the current path in the arc column have been drawn. Comparing voltage measurements for the same current and different arc lengths, finally, the sum of cathode and anode sheath voltages as well as the mean electric field strength of the arc column have been determined. Sheath voltages increasing from 18 to 23 V for pulse currents from 350 to 650 A and a mean electric field of about 1.1V mm(-1) in the arc column, which is almost independent of the current, have been obtained. As a consequence, the Ohmic heating in the arc column contributes less than 20% to the overall power budget whereas the contribution of the electrode sheathes is larger than 60%.