Study of the anode energy in gas metal arc welding

Abstract

Recent research of gas metal arc welding (GMAW) has proved that the sheath voltage dominates the total voltage fall in the current circuit and provides the most energy to the wire and the weld pool. In this paper, the energy delivered to the wire anode is studied experimentally for a typical pulsed GMAW process in the one drop per pulse mode to provide a more complete picture of the energy balance of the process. Welding of mild steel under Ar with 2.5% CO2 with different peak currents from 350 to 650 A and constant wire feed speed of 4 m min−1 as well as constant arc height are considered. The processes were studied with non-intrusive optical methods, i.e. without strong modifications. The droplet energy was determined by high-speed two-colour pyrometry and an analysis of the droplet surface temperature and geometry. In addition, Joule heating in the wire anode was also estimated from surface temperature measurements. It was found that the averaged droplet energy is almost independent of the peak current and approximately one-third of the total electric energy. A voltage equivalent of the energy delivered to the wire anode from the plasma was defined. Substracting the work function of iron, the value of this voltage is in the range of 3.25± 0.43 V and increases by 0.5 V when the current increases from 350 to 650 A. The sum of the cathode and anode sheath voltages have been estimated to be in the range between 18 and 23 V in preceding works.