Commercial solid freeform fabrication (SFF) systems, which have been developed for fabrication of wax and polymer parts for form and fit and secondary applications, such as moulds for casting, etc., require further improvements for use in direct processing of structural ceramic and metal parts. Defects, both surface as well as internal, are undesirable in SFF processed ceramic and metal parts for structural and functional applications. Process improvements are needed before any SFF technique can successfully be commercialized for structural ceramic and metal processing. Describes process improvements made in new SFF techniques, called fused deposition of ceramics (FDC) and metals (FDMet), for fabrication of structural and functional ceramic and metal parts. They are based on an existing SFF technique, fused deposition modelling (FDM) and use commercial FDM systems. The current state of SFF technology and commercial FDM systems results in parts with several surface and internal defects which, if not eliminated, severely limit the structural properties of ceramic and metal parts thus produced. Describes systematically, in detail, the nature of these defects and their origins. Discusses several novel strategies for elimination of most of these defects. Shows how some of these strategies have successfully been implemented to result in ceramic parts with structural properties comparable to those obtained in conventionally processed ceramics.

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Silicon nitride ceramics have been prepared using the fused deposition (FD) process in a Stratasys 1650 modeler. Two types of silicon nitride have been prepared: GS44 and AS800. AS800 is processed and used at higher temperatures than GS44. The strength of machined surfaces of either type of silicon nitride prepared using FD is comparable to conventionally processed material. Using standard build conditions strengths for as-built and as-sintered surfaces are approximately 50% lower. The additive nature of solid freeform processes also allows multi-material combinations to be deposited which result in enhanced performance. For example, combinations of silicon nitride based materials with different thermal expansion coefficients have been prepared which demonstrate strength increases > 20%. In addition, components containing complicated internal cavities may also be fabricated.

Fused Deposition of Ceramics (FDC) is a Solid Freeform Fabrication (SFF) technique under development at Rutgers University. This technique is based on Fused Deposition Modeling (FDM)2, a commercially available SFF technology. Freeform fabrication of ceramic and metal parts is a means of significantly lowering the cost of currently expensive components. The feasibility of Fused Deposition of Ceramics (FDC) has been demonstrated in the recent past. Crucial to the viable fabrication of ceramic components is the elimination of defects in the parts. Apart from some of the usual traits of SFF techniques, some distinct features of FD Processing lead to defects in fabricated parts. The focus of this work is to study and improve the build procedure of FDM, thereby reducing the defects that are associated with FD processing. Predictable errors in the FDC/FDM components need to be consistently eliminated to increase the yield of fully dense, defect free, green parts. Changes in the manufacturing procedure and operation of FDC are shown to reduce these errors. Fully dense green components are further processed to obtain defect free fully dense sintered ceramic parts.

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