Pressure-assisted binder jet additive manufacturing of solid propellants

Solid propellants are used as an energy source in many applications such as space launch, tactical, and gun propulsion. In traditional fabrication methods, solid propellants are cast or extruded into cylindrical mandrels. The resulting propellants are highly dense, durable, and have uniform composition. These characteristics provide consistent and reliable thrust, but do not provide a way to throttle or alter the thrust profile once ignited. Additive manufacturing (AM) holds the promise of facilitating precise control over thrust and propulsion by spatially manipulating the macro-and micro-structures of a solid propellant. However, this advantage is often accompanied by trade-offs in other crucial characteristics, including solids loading, density, mechanical properties, and consequently burning performance. Here, we report, for the first time, the use of a pressure-assisted binder jetting (PBJ) AM process to manufacture solid propellant materials. The PBJ process shows great promise in the fabrication of highly resolute propellants with high solids loading, sufficient density, and sufficient mechanical properties. Particular emphasis is given to the effects of process parameters including applied pressure and step-over on the density and solids loading (up to 85.5% and 96.1%, respectively) of printed propellants. Mechanical properties of printed propellants are analyzed and compared with those achieved by other traditional fabrication and AM methods. The results demonstrate that our method can fabricate propellants with sufficient tensile strength, elongation, and E-modulus (up to 0.88 MPa, 9.1%, and 20.7 MPa, respectively). Solid propellants with complex grain geometries and changeable burn rates (e.g., variations of 90%) were printed to showcase the capability of the PBJ process in tuning the burning behaviors of propellants in situ.