Optimising the welding conditions to determine the influence of shielding gas on fume formation rate and particle size distribution for gas metal arc welding
An automatic voltage control technique, to optimise gas metal arc welding (GMAW) conditions for minimised fume generation, was compared to conventional constant-voltage operation on the influence of shielding gas on fume formation rate (FFR) and particle size distribution. Significant reductions in FFR were attributed to reductions in the arc length and current and to improved metal transfer stability, achieved by promoting the ‘drop-spray’ transfer condition and reducing repelled globular transfer. A general decrease in average particle size was observed when using the automatic control technique for the O2-bearing shielding gases, which is significant, as finer particulates are more likely to be inhaled into the lungs. The proposed mechanism to explain this behaviour was lower arc temperatures combined with an increase in the availability of oxygen, leading to nucleation of large amounts of extremely fine fume particles when the supercooling of the vapour was large. FFR increased as CO2 content increased due mainly to the dominant influence of CO2 on metal transfer and arc characteristics. It is recommended that the influence of shielding gas on FFR should be investigated using optimised welding conditions for each shielding gas composition for GMAW, especially when operating in the spray regime.