The fundamental operation in binder jet 3D printing is the deposition of liquid binder into a powder layer to selectively bond particles together. Upon droplet impact, the binder spreads into the powder bed forming a bound network of wetted particles called a primitive. A computational fluid dynamics framework is proposed to directly simulate the capillary and hydrodynamic effects of the interfacial flow that is responsible for primitive formation. The computational model uses the volume-of-fluid method for capturing dynamic binder-air interfaces, and the immersed boundary method is adopted to include particle geometries on numerical Cartesian grids. Three-phase contact angles are prescribed through an interface extension algorithm. Binder droplet impact on powder beds of varying contact angle are simulated. Furthermore, the numerical model is used to simulate liquid bridges connecting binary and ternary particle systems, and the resulting capillary and hydrodynamic forces are validated by comparison with published experimental and theoretical model results.

Wide-scale adoption of binder jet 3D printing for mission-critical components in aerospace, biomedical, defense, and energy applications requires improvement in mechanical properties and performance characteristics of end-use components. Increased fidelity may be achieved with better understanding of the interfacial physics and complex fluid-particle interactions fundamental to the process. In this work, an experimental testing apparatus and procedure is developed to investigate the fluid and particle dynamics occurring upon impact of jetted binder droplets onto a powder bed. High-speed, microscopic imaging is employed to capture short time-scale phenomena such as ballistic particle ejection, capillary flow, and particle clustering. The effects of different process parameters (e.g., translational printhead velocity, jetting frequency, and impact velocity) on the dynamics of Inconel powder are studied. These experiments reveal that the fluid-particle interaction is significantly affected by a combination of printing parameters, ultimately governing the quality and performance of binder jet 3D printed components.