Powder-binder interaction in binder jetting process: a simulation study on bimodal powders

Binder Jetting (BJT) is a room-temperature powder-bed additive manufacturing process suitable for a wide range of materials such as bioceramics, sand, metals, and polymers. In this process, powder-binder interaction, which is influenced by the powder bed packing density during the printing process, has a major impact on the overall part quality. Although few recent studies have explored the modeling of the binder-jetting process, they are not realistic (e.g., 200 % larger droplet size when compared to the actual process). This study is the first to report a systematic study into the powder-binder interactions for bimodal powders with actual binder-jetting conditions across a wide range of packing densities and binder-jetting conditions. This integrated Discrete Element Modeling (DEM - powder spreading) - VOF (Volume of Fluid - binder interaction) study analyzed the powder-binder interaction in terms of: penetration depth, spreading time, and area per droplet on the powder bed. It was observed that an increase in droplet velocity resulted in deeper penetration (5.4%) of the binder but reduced the area of spread (20.8%) across packing densities. In addition, for a given droplet size and packing density, an increase in droplet velocity resulted in a shorter spreading time (27.3%). Findings from this study provide a new understanding of the temporospatial characteristics of the binder-powder interaction, which helps in identifying optimal printing parameters for a bimodal powder feedstock.