Optimization of metal transfer in rutile flux-cored arc welding through controlled CO2 concentration in argon-CO2 shielding gas

In this study, we analyzed the impact of carbon dioxide concentration in argon-carbon dioxide shielding gas on droplet transfer characteristics in rutile flux-cored arc welding, employing titanium oxide as a primary wire flux component. The welding process was carried out at a welding current of 190, 220, 250, 280, and 310 A under an argon-CO2 shielding gas mixture with six levels of CO2 concentration of 0, 5 %, 10 %, 15 %, 20 %, and 25 % for a parametric study. Unlike the conventional solid wire welding trend, where the droplet transfer frequency decreases with the increase in carbon dioxide concentration, an increase in metal transfer frequency was observed with the increase in CO2 concentration from approximately 5 % to 20 %. The concentration reaching the maximum frequency was 20 % at 190 A, which decreased as the welding current increased, reaching 5 % at 310 A. Droplet initiation at the lower sheath end is succeeded by a gradual downward movement along the flux column's side after a few milliseconds. Upon reaching the lower end, the droplet forms a neck and undergoes separation. Thus, the length of the flux column directly impacts the duration of one droplet transfer cycle. The length was decreased by arc constriction when increasing CO2 concentration appropriately to concentrate beneath the flux column or by increasing the welding current to raise the arc temperature, which contributed to melting and shortening the flux column.