Numerical analysis and experiment validation of droplet transition types for thermal fluid dynamics in wire arc additive manufacturing CuCrZr alloy

Achieving high deposition quality in CuCrZr alloy fabricated by wire arc additive manufacturing (WAAM) is critically important for ensuring structural integrity and performance. Investigating the dynamic behaviors and evolution of droplet-molten pool interactions could reveal forming influence mechanisms and aid stability control of WAAM CuCrZr alloy. This study investigates the influence of arc length on forming characteristics. Deposition experiments demonstrate that arc length significantly affects deposition dimensions and forming stability. Variations in arc length lead to distinct droplet transition types: continuous bridge transition and free transition. In bridge transition, the wire maintains continuous contact with the molten pool, whereas free transition involves a cyclical process of wire melting-droplet growth-droplet fall into the molten pool. Based on experimental observations, the three-dimensional droplet-molten pool coupling models were established . Multi-physics characteristics including thermal and flow fields were explored. Experimental and simulation results demonstrate good agreement. The maximum temperature of molten pool increased from 1580 K in bridge transition to 1680 K in free transition, indicating elevated energy within the molten pool. Consequently, the formed width expanded while the height diminished. Under free transition, the maximum flow velocity accelerated, intensifying flow motion. The enhanced momentum input increased molten pool turbulence, leading to greater instability in the deposition process. The results demonstrate that a relatively stable molten pool during bridge transition improves deposition stability. This study provides valuable theoretical insights into the molten pool dynamics of CuCrZr alloys and contributes to enhancing the stability of WAAM processes.