Design of a slurry layer forming station and improved fluid handling system for raster processes in 3DP®

Abstract

Three-Dimensional Printing (3DPTM) is a rapid-manufacturing process originally developed at MIT for building parts directly from CAD-generated models. Parts are fabricated in "slices" by creating a complete layer of powder and then selectively joining powder particles with a polymer binder deposited using a moving printhead. Traditional 3DPTM builds layers by spreading dry powder and prints binder using a rastering scheme with a continuous-jet printhead. For smaller parts and greater accuracy, a variation on the process called slurry 3DPTM (s3DPTM) uses raster-built slurry layers and a vector-printing scheme with a drop on demand (DoD) printhead. This here thesis presents efforts to improve core technology in both dry-powder 3DPTM and slurry 3DPTM. One of the most critical steps in s3DPTM is the building of the slurry layers. To avoid intra- and interlayer defects the slurry layer must be rastered at high deposition rates to promote line merging and better layer quality. The difficulty lies in the design of a machine capable of oscillating the slurry nozzle at the required frequencies. Fortunately, such a design was completed and the machine built as part of a collaborative effort with TDK Japan to build an s3DPTM machine for manufacturing small parts. The design uses a reciprocating countermass strategy to recycle mechanical energy and eliminate troublesome vibrations. A general overview of this slurry layer forming station (LFS) is given, along with an in-depth treatment of several components, including the forcers, centering system, and interface software. And speaking of rastering, dry-powder 3DPTM relies on this strategy for printing binder, just as the LFS uses a raster method to build powder layers. Beginning with observations made during the design of the LFS, the fluid-handling system was redesigned to improve binder droplet stream stability during the carriage traverse and turnaround. The improvement was made possible by repositioning a smaller version of the "Clamshell" constant pressure vessel used to set the fluid flow rate to the printhead carriage itself and using a closed-loop control system to maintain a constant fluid level in the Clamshell. Drawings, parts lists, schematic diagrams, and assembly instructions are included for building additional fluid control systems.