Influence of shielding gas on undercutting formation in gas metal arc welding

Two sets of vision-based sensing systems were established to investigate the behavior of droplet transfer, arc shape and molten metal flow by varying shielding gas mixtures. Orthogonal experiments and analysis of variance indicated that the CO2 content in shielding gas was the major welding parameter compared with welding current and arc voltage, which affected the size of undercutting defects. Results demonstrated that the suppression of undercutting defects was mainly caused by the reduction in backward flow velocity of molten metal in weld pool due to the lowering in droplet impact and arc force when CO2 content increased from 10% to 100%. Non-dimensional fitting method was used to establish the relationships between welding parameters and undercutting defects. It showed that appropriate pulse welding current could suppress undercutting and spatter with high CO2 content in shielding gas.