The process-property-performance relationships of feedstock materials used for fused deposition of ceramics (FDC).

摘要

Fused deposition of ceramics (FDC) is an extrusion based layered manufacturing process. It uses a high solids loaded (>50 vol. % ceramic or metal powder) thermoplastic binder in filament form as the feedstock material. The filament acts as both the piston driving the extrusion process and the feedstock material being deposited in the X-Y direction onto a Z-stage platform. The primary mode of failure of the filament during the FDC process is via buckling. In this study, the effect of some of the FDC process, machine and material parameters on filament buckling were examined.; It was found that for a given set of FDC machine and process parameters, the filament materials with a higher ratio of compressive modulus to apparent viscosity were less likely to buckle during FDC. It was also established that filament materials with a value of compressive modulus to viscosity ratio greeter than some critical value (3–5 × 105 1/s for 0.508 mm diameter FDC nozzle) did not buckle during FDC.; The experimental results indicate that FDC extrusion pressure increases with: decreasing diameter of FDC nozzle, increasing length of nozzle tip and increasing volumetric flow rate.; It was found that it is possible to decrease the filament material's viscosity (for a given polymer chemistry and solids content) through the use of suitable surface agents which, modify the particle-polymer interface chemistry but not the filament material's modulus. Therefore, for a given polymer system the only feasible way to decrease the chances of a filament buckling during FDC, using a materials design approach (i.e. increase modulus to viscosity ratio) is to decrease the viscosity of the filament. In order to modify the modulus it is necessary to modify the polymer chemistry itself.; It was concluded that a mechanical approach, by modifying some FDC machine design parameters (such as the rollers-liquefier gap) or developing an alternate feed mechanism (such as a micro-screw extruder) will be more efficient (than a materials design approach) in mitigating (or even eliminating) the filament buckling problem. The mitigation (or elimination) of the filament buckling problem will in turn relax the constraints on the FDC filament material properties (stiffness and viscosity) and allow for easier and faster development of new materials to be used in fused deposition of ceramics.