Droplet transfer behavior in bypass-coupled wire arc additive manufacturing

The bypass-coupled wire arc additive manufacturing (WAAM) process was studied, and the arc characteristics and droplet transfer behavior during the deposition process were examined. The effects of the bypass current, wire feeding speed, wire feeding height, and wire feeding angle on the droplet transfer mode were investigated via a single variable experiment. The results show that with an increase in the bypass current, the arc first shrinks and then expands, and the corresponding droplet diameter and transfer period vary. There are two primary modes of droplet transfer during the deposition process: free droplet transfer and bridging transfer. When the transfer process is in the bridging transfer mode, a smooth deposition wall is obtained. As the wire feeding speed increases, the transfer mode of the droplet gradually changes from the free transfer mode to the bridging transfer mode. The larger the distance between the wire tip and the surface of the base metal, the higher the wire feed speed required to achieve bridging transfer. There is a linear relationship between the droplet diameter and the cubic root of the wire feeding speed. Finally, the droplet transfer behavior is discussed using droplet force analysis.