Numerical investigation of influencing factors on binder migration in the powder bed during metal binder jetting

Abstract During metal binder jetting (MBJ), powder bed density critically governs binder migration and influences the final properties of the components. Heterogeneous powder bed density distribution in a single powder spreading process, possibly arising from both powder characteristics and spreading conditions, can lead to non-uniform binder saturation patterns. For process optimization in practical manufacturing, adjusting the spreading process is often more efficient than altering the powder that may have been chosen to meet final property requirements. However, the influence of process-controlled variations in powder bed density on binder migration has not yet been sufficiently addressed, and independent studies of powder spreading or binder deposition are not sufficient to capture the sequential effects. To fill this gap, this study integrated powder spreading simulations under varying spreading conditions using the discrete element method (DEM) with binder deposition simulations by computational fluid dynamics (CFD), in which the spread stainless steel 17-4PH powder beds served as the initial condition of binder deposition. The results of single-droplet simulations reveal that increasing the powder bed density initially promotes lateral binder spreading and suppresses vertical binder penetration, however, it ultimately results in a deep penetration. When extended to the more realistic multiple-droplet simulation, decreasing the droplet spacing was found to delay the local equilibrium saturation but promote the binder migration. A series of innovative single-layer printing experiments adopting the corresponding settings in the simulations confirms the validity of the developed workflow.