Defect-controlled binder jetting (BJT) additive manufacturing through dimensionless mapping of binder spreading and penetration

Binder jetting (BJT) a metal additive manufacturing process with broad material compatibility. The resolution of the printed parts is dependent on binder-powder interaction and the mechanisms that infiltrate binder into the powder bed during printing, and controlling the defects related to this infiltration, such as balling and bleeding. Binder spreading and penetration are dependent on capillary suction and viscous resistance of the powder bed, which are depicted by the packing density of the spread powder layer. Prior studies have only emphasized strategies to increase the powder packing density. Here, a systematic analysis of powder packing density and binder infiltration dynamics shows that neither loose packing nor tight packing is suitable for defect-free printing. Therefore, two dimensionless numbers: binder penetration number, Bp, and binder spreading number, Bs, are introduced that collapse all binder material properties, binder deposition-related process parameters, and powder properties to provide the range of powder packing density for defect-free printing. This work establishes the foundation for developing customized binders for printing new materials, expanding the material compatibility of the BJT process.