Testbeds for Advancement of Powder Bed Additive Manufacturing with Application to Reactive Binder Jetting of Ceramics

Abstract

Binder jet additive manufacturing (BJAM) offers design flexibility and compatibility with a variety of materials due to material processing in the solid state. The formation of the powder bed is a critical step to ensuring quality parts are produced via binder jetting, but low powder bed densities and a lack of understanding of the effect of recoating parameters have limited the applicability of binder jet components. Furthermore, polymer-based binders are most commonly used despite the need for a debinding step and challenges with part warping during sintering. Adaptations to the binder jet AM process, such as the use of powder spreading optimization and reactive binders, could facilitate the development of high-density ceramics from dry powder feedstock. To attain this, an understanding of powder spreading, binder-powder interactions, and reactive metal salt decomposition and interparticle-bridge evolution is required.

This thesis: (1) describes the design and fabrication of testbeds for powder spreading, ink jetting, and binder jetting processes, (2) explores the effects of powder feedstock and spreading parameters on powder bed density and uniformity of alumina ceramics for application in binder jet additive manufacturing, (3) establishes a process for novel binder ink development and applies it to the production of reactive metal salt binders for preceramic binder jetting, and (4) fabricates alumina ceramic components through BJAM and compares the efficacy of polymer and reactive binders in microstructural and dimensional control during post-process sintering. The powder spreading and BJAM testbeds are validated using representative experiments to characterize powder layer and green component fabrication. By coupling the powder spreading tested with an x-ray-based powder layer density measurement methodology, the influence of powder size and shape distribution, as well as spreading and dispensing methodologies is interrogated. A process including characterization of ink rheology, jetting properties, decomposition, and green strength is applied to the development of novel reactive binders with sustained strength during sintering. Finally, the BJAM testbed is utilized to fabricate ceramic components using polymer and reactive binders, showcasing the capability for microstructural and dimensional control of ceramics through the use of reactive binders.