Freeform fabrication methods build materials by the repetitive addition of thin layers. This approach can be applied to build parts from epoxy resin which is modified with a gelling agent to solidify the material until curing occurs. High strength and stiffness parts can be obtained through fiber reinforcement but the fiber content is limited by packing effects. We have found that a combination of two types of fibers can be used to achieve higher strength and stiffness than can be obtained from a single fiber type.

An alternative route to reinforcement is to form the reinforcing phase after the material is deposited by an in situ reaction. This approach has been applied to the use of freeform fabrication to make bars of mineralized gel and of methacrylate-silica hybrids. Good mechanical properties can be attained in each case, with up to 50 vol.% inorganic phase and bend strengths in the range from 50-100 MPa.

Automotive and heavy-duty friction materials are complex multimaterial composites that contain, besides polymers and fibers, a number of constituents whose exact role is not well delineated. Since the performance of these composites requires not only uniform frictional properties but also complex shapes, advanced formation techniques are required. However, before these techniques can be harnessed, we attempted to understand how nitrile rubber-modified phenolic polymer's structural and thermal behaviors were modified by the incorporation of materials such as BaSO4, graphite, coal tar pitch, slag fibers, alumina, and silicon carbide, typical friction composite ingredients. The formed composites were examined by FTIR, DSC, and DMA techniques at 300 K < T < 600 K. Our results suggested that the incorporation of ingredients, singly and additively, strongly affected the thermomechanical properties of the formed

Amorphous carbon and infrared absorbing glass particulate additives to polyethlene terephthalate increased its infrared absorptance. Significantly lower volume concentrations of carbon were required for a given absorptance increase; however, test bars with glass additive concentrations displaying ˜90% absorptances were largely aesthetically unaltered. Carbon additions to produce the same infrared absorptance resulted in nearly opaque test bars. Heat transfer calculations showed preform heatup time could be reduced from 1 s to 0.6 s with glass particle additions

Stereolithography patterns have been used to create composites with gradient properties. Patterns are produced with an open cellular or columnar structure inside a surface shell. This serves as a host for filler materials, generally epoxies or polyurethane matrices loaded with various fibers or microspheres. Regions within a single object may be separated by thin barriers, allowing filling with different matrix materials to create regions of differing local properties. The internal structure can also be continually gradated in dimension to produce composites with properties ranging from that of the filler material to that of the SFF material, currently epoxy or ABS plastic. This is a general set of processes that can be applied to a variety of existing Solid Freeform Fabrication systems.

3D-LCVD of nickel and iron carbonyls was studied in order to grow 3-D metal forms under static or scanning Nd:YAG-laser beam. In addition to growth, emphasis was also placed on the prevention of the simultaneous decomposition of carbon monoxide, which interferes with the metal growth process. This was essential, because the fairly high precursor gas pressures of the metal carbonyls are very tempting for the 3D-LCVD. Parameters to be optimized included precursor pressure, laser power, laser scan speed and spot size. In order to optimize the growth parameters, the microstructures of the resulting forms were studied using SEM. Comparison between static and scanning growth is presented with the building philosophy in mind, e.g. whether to build structures layer by layer, from modules or in conjunction with another process to compensate for their shortcomings. The substrates used included steel, graphite and porous bronze.

The results indicated different microstructures for iron and nickel, which were dependent on the total/precursor pressure. In the scanning experiments, nickel produced very thin films of high reflectivity, whereas iron produced a structure which could be described as a crystalline spider's web. The static experiments produced solid rods in the case of nickel, whereas with iron, the rods were hollow, even with same spot sizes. Moreover, an evident change in the microstructure of the nickel forms as a function of pressure was observed. The 3-D growth rate of the static experiments seemed very promising for the forthcoming scanning experiments.

In this work, the deposition of silicon carbide lines using a tetramethylsilane (TMS) precursor was investigated. Effects of target temperatures on the morphology and crystal structure of the deposits were examined. It was found that the morphology of the SALD SiC depends strongly on the target temperature. The contour of the cross section of the SiC deposits changes from a triangle to trapezoid to volcano shape and the surface morphology of the deposited lines changes from smooth to rough to porous as the target temperature increases. A critical target temperature was found to be about 700°C to initiate deposition of SiC under the current experimental configurations. X-ray diffraction analyses show that the SALD SiC formed at 1000°C contains both crystalline and amorphous phases. The results are briefly discussed.

This paper presents the development of Selective Laser Sintering/Hot Isostatic Pressing (SLS/HIP) technology for production of functional high performance components in the titanium alloy Ti-6AI-4V. SLS/HIP is a net shape manufacturing technique that combines and exploits the freeform shaping capability of selective laser sintering and the full densification capability of hot isostatic pressing. The advantages of SLS combined with in situ HIP encapsulation include single step net shape canning, full densification by containerless HIP, no container-powder adverse interactions, reduced pre-processing time, and minimal post-process machining compared to conventional HIP of canned powders. Microstructure and mechanical properties of SLS processed and HIP post-processed Ti-6A1-4V are consistent with conventionally processed material. The potential of SLS/HIP technology was demonstrated by net shape fabricating a component to specification, namely the titanium guidance section housing base for the AIM-9 Sidewinder missile.

Rapid Fabrication of three-dimensional shapes of engineering materials such as H 13 tool steel and Nickel super alloys are now possible using Direct Materials Deposition (DMD) technique. H 13 tool steel is one of the difficult alloys for deposition due to residual stress accumulation from martensitic transformation. However, it is the material of choice for the die and tool industry. DMD offers Copper chill blocks and water cooling channels as the integral part of the tool. On the other hand ZrO2 was co-deposited with nickel superalloys using DMD. This process thus is amenable to produce both macro and microstructure to a designed specification. This paper briefly reviews the state of the art of DMD and describes the microstructure and mechanical properties of selected engineering alloy systems deposited by DMD.

Direct fabrication of metal near-net shapes from a computer model typically involves melting and solidification, which can cause high residual stresses, undesirable phases, poor microstructures, rough surface finishes, warpage, and other problems. This paper describes a new technology, still under development, that might be used to directly fabricate solid, near-fulldensity, free-form shapes of many metals, and even some composite materials, at or near room temperature without melting and solidification. In this process, tentatively called Cold Spray Direct Fabrication (CSDF), powder particles in a supersonic jet of compressed gas impact a solid surface with sufficient energy to cause plastic deformation and consolidation with the underlying material by a process thought to be analogous to explosive welding. Material deposition by cold spray methods has already been successfully demonstrated by several investigators. This paper presents results of an experimental study to investigate the effects of selected process variables on cold spray particle velocities. In addition, a key technical barrier to the CSDF concept is focusing the spray stream down to dimensions that would permit a useful level of part detail, while still providing practical build rates. This paper presents results of initial research to develop an aerodynamic lens that may provide the required particle stream focusing.

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.

Novel piezoelectric ceramic and ceramic/polymer composite structures were fabricated by solid freeform fabrication (SFF) for sensor and actuator applications. SFF techniques including fused deposition of ceramics (FDC) and Sanders prototyping (SP) were utilized to fabricate a variety of complex structures directly from a computer aided design (CAD) file. Novel composite structures including volume fraction gradients (VFG) and staggered rods, as well as actuator designs such as tubes, spirals and telescopes were made using the flexibility provided by the above processes. VFG composites were made by SP technique with the ceramic content decreasing from the center towards the edges. This resulted in a reduction of side lobe intensity in the acoustic beam pattern. The FDC technique was used to manufacture high authority actuators utilizing novel designs for the amplification of strain under applied electric field. The design, fabrication and electromechanical properties of these composite and actuator structures are discussed in this paper.

The Fused Deposition of Ceramics (FDC) process is an extrusion based layered manufacturing technique. In this study, the microstructural and property homogeneity of GS44-Si3N4 parts made by FDC is examined. The feedstock, green, and sintered parts were examined using characterization techniques such as optical and scanning electron microscopy, x-ray radiography, and x-ray diffraction. In addition, mechanical properties (σf, and Klc), shrinkage, and warpage results were used to characterize the FDC parts. It was found that by using proper build parameters and tool paths, dense, homogenous, near-net-shape GS44-Si3N4 parts can be fabricated. While the mechanical properties of these parts are shown to be isotropic, there is some degree of texturing detected with XRD. Si3N4 filament feedstock intentionally textured with 5.5 vol% of β-seed particles has also been made.

The Fused Deposition of Ceramics (FDC) technique was used to fabricate ceramic skeletons for development of piezoelectric composite transducers for medical imaging. The green parts were designed in order to have 30 vol% of PZT-5H ceramic in the final composites. Physical characterization of the sintered samples revealed that 96% of the theoretical density was achieved. Optical microscopy showed that defects, such as small roads and bubbles were eliminated due to powder processing improvements. The electromechanical properties of the final composites were found to be similar to properties obtained for conventionally made composites.

A scientific methodology to characterize the critical mechanical properties of feedstock material for fused deposition of ceramics has been developed. A detailed discussion of the methodology of mechanical characterization and results for lead zirconate titanate (PZT) fused deposition of ceramics (FDC) feedstock is presented. The effect of storage time, temperature and crosshead displacement rates on the mechanical properties of the PZT FDC feedstock was studied. The modulus and the failure stress increase with displacement rate. The modulus and failure stress decrease with temperature indicating the necessity for cooling filaments prior to entrance to liquefier. The modulus also decreases with storage time in 50% RH while failure strain increases with storage time in 50% RH.

Direct ceramic stereolithography (SLA) is done using UV-curable suspensions of powders in acrylates in a conventional SLA machine. Hydroxyapatite prototypes for bone tissue scaffolds are built from Image-Based Design files, featuring an interior architecture of void passages. Complex alumina objects are built as digital sculptures. Piezoelectric ceramic actuators from PZT, which are difficult to photocure, are built using indirect stereolithography, where SLAbuilt epoxy molds are used to form a thermal-cured suspension of PZT powders. We report on the thermal-curing behavior of the suspensions, and the fundamentals of part building.

Solid freeform fabrication of aqueous alumina (Al2O3)-poly(vinyl alcohol) (PVA) gelcasting suspensions was carried out using a computer-controlled extrusion apparatus fitted with a two-nozzle delivery system. The impact of casting parameters (e.g., tip diameter, mixing rate, etc.) and suspension composition on line resolution/uniformity, printability, and as-cast component properties was probed using laser profilometry and optical microscopy. Line uniformity depended on mixing rate (Rmix) and tip diameter (td) for the chamber and paddle geometry utilized. These data were used to establish processing maps that identify optimal print conditions for varying suspension composition.

Robocasting is a freeform fabrication technique for dense ceramics and composites that is based on layer-wise deposition of highly loaded colloidal slurries. The process is essentially binderless with less than 1% organics and parts can be fabricated, dried, and completely sintered in less than 24 hours. This review will highlight materials developments for structural applications and modelling of slurry flow. Fabrication of preforms for alumina / metal composites will be discussed as well as techniques for multimaterial deposition in both graded structures and discrete placement of fugitive materials.

A conventional rapid prototyping technology has been used to build prototypes using direct deposition through a drop-on-demand ink-jet printing system. Al2O3 - filled waxes have been developed with viscosity values close to those of the materials used in commercial printing systems. Commercial dispersants based on stearic acid and sterylamine have been studied and stable ceramic suspensions with ceramic volume fractions in the range 20–40 volume% produced with suitable viscosity. A suspension of 20% Al2O3 in an alkane wax has been successfully printed.

In order to successfully build three-dimensional shapes by hot-melt inkjet deposition it is essential to control the building block characteristics, i.e., the deposit geometry, dimensions and fine feature resolution. The deposit formation is mainly dependent on the material systems and their jetting behaviour. It is therefore crucial to understand how the jet formation is affected by the inks 'rheological properties and how to manipulate the jet-head driving parameters to achieve optimum deposition conditions. This paper reports our investigations with a model jet firing station, about the influence of driving parameters of hot-melt drop-on-demand print-heads (e.g., pulse shape and frequency) on the jet and deposit formation characteristics, for both unfilled and powder loaded vehicles.

The Three-Dimensional Printing (3DP™) process has been modified to incorporate colloidal science for the fabrication of fine ceramic parts. Complex shaped alumina and silicon nitride components have been formed directly from 3-dimensional CAD files using submicron powders. Parts were built using a sequential layering process of the ceramic slurry followed by ink jet printing of a binder system. A well dispersed slurry and optimized printing parameters are required to form a uniform powder bed with a high green density. Liquid-powder bed interactions affect the geometry and internal structure of the component. The redispersion of the unprinted powder bed is critical in order to retrieve the printed components. The slurry and powder bed chemistry are the major factors controlling powder bed redispersion. The process is generic and can be readily adapted for new materials systems. Our research is currently focused on the fabrication of dielectric RF filters. Preliminary results have demonstrated the ability to successfully fabricate cylindrical RF resonators.