Capillary pressure and saturation of pore-controlled granules for powder bed binder jetting

Powder bed binder jetting (PBBJ) is an additive manufacturing process in which a liquid binder is selectively deposited onto a powder bed to join the powder particles. These deposited parts, called the “green body,” are shaped by ink-jetting a liquid binder onto the powder bed. For liquid binders to be fully cured in the intended area of the powder bed, interaction between the droplets of the liquid binder and layered powder bed is important. This interaction leads to spreading of the binder (lateral migration) and infiltration (vertical migration) in the powder bed; however, it can be adjusted for geometrical accuracy of green body. This study confirms that saturation and penetration depth of the binder in the powder bed is related to the capillary pressure at initial saturation. The capillary pressure differs based on the amount of pores on the surface of dry powder particles. The powders in this study were prepared as granules produced by a spray dryer process with sintering. The different initial saturation capillary pressures of the prepared dry powders were compared with the penetration ratios by comparing the penetration depth and spread diameter. The results confirmed that the penetration ratio was determined by the capillary pressure.