Real-time observation and numerical simulation of the molten pool flow and mass transfer behavior during wire arc additive manufacturing

In the wire arc additive manufacturing (WAAM) process, the flow behavior of the molten pool determines the formation accuracy and formation defects. Therefore, it is significant to understand the complex physical process of the molten pool behavior in the WAAM. A real-time X-ray direct observation method and volume of fluid method (VOF) were performed to study the flow in molten pool and liquid flow in the molten pool. X-ray was used to observe the liquid flow in the molten pool and the droplet transfer from the WAAM. A three-dimensional model of the molten pool and droplet was established based on the VOF method, and the temperature distribution and flow status of the molten pool were calculated. By controlling different wire feeding speeds, two different droplet transfer modes were observed by X-ray, which include globular transfer and bridging transfer. Compared with globular transfer, bridging transition has little effect on molten pool flow. The flow model during the deposition process is established; the x-z plane is divided into four regions according to the flow characteristics of different positions in the molten pool. The maximum velocity in the molten pool appears in the action area of plasma arc force, which is 0.277 m/s, which leads to the increase in melting depth and promotes the flow of molten metal.