Stephen C. Danforth

Structural quality of parts processed by fused deposition

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.

Processing of advanced electroceramic components by fused deposition technique

Abstract A variety of advanced ceramic components were fabricated using the fused deposition of ceramics (FDC) process. In FDC, ceramic loaded polymer filaments are used to build parts in a layer-by-layer fashion. A process map, based on the compressive strength and modulus of the FDC feedstock, was developed to predict the feasibility of deposition with a variety of FDC filaments. Alumina structures with photonic bandgap properties were deposited for high frequency (GHz) applications. Net shape bismuth titanate components with oriented grains were fabricated by pre-alignment of small volume of seeds in green FDC parts, followed by grain growth treatment. Piezoelectric actuators with novel structures such as spiral and bellows were manufactured and studied.

A novel system for fused deposition of advanced multiple ceramics

In this article we present the system that we have developed at Rutgers University for the solid freeform fabrication of multiple ceramic actuators and sensors. With solid free form fabrication, a part is built layer by layer, with each layer composed of roads of material forming the boundary and the interior of the layer. With our system, up to four different types of materials can be deposited in a given layer with any geometry. This system is intended for fabrication of functional parts; therefore the accuracy and precision of the fabrication process are of extreme importance.

Chemical vapor processing and applications for nanostructured ceramic powders and whiskers

Abstract A new chemical synthetic process for producing non-agglomerated nanostructured ceramic (n-ceramic) powders from metalorganic precursors is described. The process combines rapid thermal decomposition of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate under a reduced inert gas pressure of 1–50 mbar. A wide variety of metalorganic precursors is available commercially, all of which can be utilized in this process to produce n-ceramic powders, including single phase, multiphase and multicomponent systems. The process has been used to synthesize nonagglomerated n-SiC x N y and n-ZrO x C y powders, with controlled particle size in the range 2–20 nm. Heat treatment of the as-synthesized n-powders in various high purity gas streams causes compositional and structural modifications, including particle purification and crystallization, as well as transformation to a whisker-like morphology. Non-agglomerated n-ceramic powders form uniformly dense powder compacts by cold pressing, which can be sintered to theoretical density at temperatures as low as 0.5 T m .

Chemical vapor condensation of nanostructured ceramic powders

Abstract This paper describes a modification of the conventional gas condensation processing apparatus in which the usual evaporative source is replaced by a chemical source. The new system combines rapid thermal decomposition and expansion of a precursor gas stream with rapid condensation of the product species on a cold substrate. We have demonstrated the feasibility of synthesizing loosely agglomerated nanoparticles (6 to 10nm) of SiCxNy, starting from hexamethyldisilazane as precursor compound. Critical to the success of this new chemical vapor condensation method (CVC) are: (1) low concentration of precursor in the carrier gas, (2) rapid expansion of the gas stream through an uniformly heated tubular reactor, and (3) rapid quenching of the gas phase nucleated clusters or nanoparticles as they exit from the reactor tube.

Development of a binder formulation for fused deposition of ceramics

A new family of thermoplastic binders has been developed for usage in fused deposition of ceramics (FDC). Mixtures were formulated consisting of a base binder, tackifier, wax, and plasticizer. The resultant formulation was chosen based on mechanical, rheological, and thermal property requirements. A formulation consisting of 100 parts base binder (by weight), along with 20 parts tackifier, 15 parts wax, and five parts plasticizer exhibited an optimized compromise of mechanical, rheological, and thermal properties. This formulation was compounded with 55 vol. per cent lead zirconate titanate (PZT) powder, and extruded into filaments with a diameter of 1.75mm and a length of approximately 50 (+/‐10) cm. The resulting filaments were used to fabricate functional piezoelectric ceramic devices via FDC. The binder development process is described, along with the associated mechanical, rheological, and thermal property data.

Solid freeform fabrication of metal components using fused deposition of metals

A new hard tooling fabrication technique, named fused deposition of metals (FDMet), to fabricate prototype metal components was investigated. This fabrication is performed directly from a computer-aided design (CAD) file without using molds, dies, or similar tooling. The FDMet process is based on a patented fused deposition modeling (FDM) and fused deposition of ceramics process where a three-dimensional (3D) object is built from a 1.75-mm diameter metal filament fed into a heated extruder head capable of moving in the X–Y direction. The head extrudes controlled and continuous flow of material onto a fixtureless platform capable of moving in the Z-direction. The process from raw material to the final prototype is described. The post processing steps include binder removal of the polymer in the green part and sintering to densify the part. To demonstrate the capability of this technique, several standard samples and hard tooling components such as a wrench and lug fit were fabricated. The accuracy and reproducibility issues are discussed.

Tool Path-Based Deposition Planning in Fused Deposition Processes

The fabrication of a functional part requires very high layer quality in the Fused Deposition (FD) processes. The constant deposition flow rate currently used in FD technology cannot meet this requirement, due to the varying geometries of the layers. To achieve a high quality functional part, an overfill and underfill analysis is conducted. A deposition planning approach is proposed, which is based on a grouping and mapping algorithm. Two piezoelectric test parts have been built to demonstrate the effectiveness and feasibility of the proposed approach.

Saint-Venant end effects in piezoceramic materials

The stress decay rate and characteristic decay length for anisotropic materials and fiber composites have been intensively investigated. However, those for piezoelectric materials have not been studied. In this paper, we examine the Saint-Venant end effects of piezoceramic materials by considering the problem of a semi-infinite piezoceramic strip polarized in the thickness direction and with applied voltages on the upper and lower surfaces. It is assumed that the gradient of electric potential in the axial direction is much smaller than that in the thickness direction. Thus, the governing equations in terms of the Airy stress function and electric potential function can be uncoupled. The governing equation in terms of the Airy stress function involves only two non-dimensional parameters after non-dimensionalization. Finally, the stress decay rates and characteristic decay lengths for a variety of piezoceramic materials are computed numerically, and their variation with the two non-dimensional parameters is presented.

Piezoelectric ceramics and composites via rapid prototyping techniques

Reviews the inherent advantages, i.e. design flexibility and processing, of manufacturing piezoelectric ceramics and composites with numerous architectures via rapid prototyping techniques. Reports on processing in which piezoelectric ceramics and composites with novel and conventional designs were fabricated using rapid prototyping techniques. Fused deposition of ceramics, fused deposition modeling, and Sanders prototyping techniques were used to fabricate lead‐zirconate‐titanate ceramics and ceramic/polymer composites via, first, direct fabrication and, second, indirect fabrication using either lost mold or soft tooling techniques.