Swing Arc Behavior and Thick-Wire Droplet Transfer Characteristics in Narrow-Gap GMAW Using Pre-Embedded Cold Wire

To improve the stability and controllability of narrow-gap welding (NGW) and systematically elucidate the mechanism by which pre-embedded cold wire modulates arc behavior and metal transfer, this study investigated the arc characteristics and metal transfer behaviors in thick-wire narrow-gap gas metal arc welding (GMAW) with a swing arc and pre-embedded cold wire. Two types of thick wires, single-strand welding wire (SWW) and cable-type welding wire (CWW), were compared under different numbers of pre-embedded cold-wire layers (n = 0, 1, 2). The results indicate that during arc swinging, the average arc spreading angle at the sidewalls is consistently smaller than that at the groove center for both wire types. For SWW, the sidewall arc spreading angle decreased by 13.1% and 18.4% with n = 0 and n = 2, respectively, compared with the groove center; for CWW, the reductions were 24.6% and 20.2%. Moreover, pre-embedded cold wire significantly increased the arc spreading angle (by up to 15.8% for SWW at the groove center) and induced deflection of arc cathode spots toward the cold wire, thereby improving heat distribution on the sidewalls and promoting sidewall penetration. In terms of droplet transfer, SWW exhibited stable spray transfer at the sidewalls and globular spray transfer at the groove center, while CWW showed rotating spray transfer at the sidewalls and a unique hanging droplet transfer mode at the groove center. The average droplet diameter of CWW at the groove center is 17% larger than that of SWW. Pre-embedded cold wire also significantly improved arc stability for both wire types, as indicated by a more concentrated voltage–current distribution, with CWW showing superior stability in the absence of cold wire, whereas no clear regularity was observed in its effect on droplet transfer. The findings suggest that pre-embedded cold wire is beneficial for applications requiring reliable sidewall fusion, as it improves heat distribution while maintaining droplet transfer stability. Further optimization of cold-wire layer number and positioning is recommended for enhanced weld quality.