Effects of active gases on droplet transfer and weld morphology in pulsed-current NG-GMAW of mild steel

Abstract

Small amount of active gases CO 2 and O 2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO 2 , being added into the pure argon shielding gas, changes from 5% to 5%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O 2 is added. Both CO 2 and O 2 are favorable to stabilizing arc and welding process. O 2 is even more effective than CO 2 . However, O 2 is more likely to cause the inclusion defects in the weld, while CO 2 can improve the weld appearance in some sense. The weld surface concavity, which is sensitive to the formation of lack-of-fusion defect in NG-GMAW, is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant.