Influence of shielding gas on fume formation rate and particle size distribution for optimised GMAW
The influence of shielding gas on fume formation rate (FFR) and particle size distribution has been investigated by using a technique developed for automatic control of the welding voltage in gas metal arc welding (GMAW). The results for automatic control are compared with the use of a fixed voltage. Significant reductions in FFR and a general decrease in average particle size were observed using the automatic control technique. This reduction in FFR was attributed to improved metal transfer stability, via a reduction in the occurrence of repelled globular transfer, by promoting the 'drop-spray' transfer condition, together with a reduction in the arc length. FFR and particle size were strongly related to the CO2 content of the shielding gas, where FFR increased as %C02 increased, due mainly to the dominant influence of CO2 on weld transfer and arc characteristics. The results indicate that FFR for GMAW in the spray regime should be determined by using optimised welding conditions for each shielding gas composition.
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