Mechanical and Rheological Properties of Feedstock Material for Fused Deposition of Ceramics and Metals (FDC and FDMet) and their Relationship to Process Performance

Fused deposition of ceramics (FDC) is a solid freeform fabrication technique based on extrusion of a highly loaded thermoplastic binder system. The present FDC process uses filament feedstock of 1.780 mm ± 0.025 mm diameter. The.filament acts as both the piston driving the extrusion process as well as the molten feedstockbeing deposited. The filaments need to be able to provide and sustain the pressure needed to drive the extrusion process. Failure to do this results in failure via "buckling". The filament compressive modulus determines the ability ofthe filament to provide·and sustain the required pressure to drive the extrusion. The viscosity ofthe feedstock material, nozzle geometry and volumetric flow rates employed determine the pressure needed to drive the extrusion process. In this worktheiextrusion pressure for a particular material termed PZT ECG9 (52.6 Vol.% PZT powder in ECG9i~inder) was measured experimentally as a function of volumetric flow rate and nozzle geometry.rhe compressive modulus ofthe material was determined using a miniature materials tester (Rheoinetrics, Inc., Piscataway, NJ). A process map has been developed. The map is based .on the quantity MIE, and predicts the performance of the material in a FDC process as a.functioIl.ofnozzleg~ometry and volumetric flow rate. In general, it is observed that when MIE exceeds a critical value, called APcr/E, there is an increased tendency for the filament to buckle. A. preliminary fluid flow model for extrusion of PZT ECG9 through a FDC nozzle has also been developed using Polyflow™ software. The model predicts the observed trend in pressure drop with flow rate and nozzle geometry with reasonable accuracy.Mechanical Engineerin