Solid Free Form Research Articles

Ceramic synthetic substrates using solid freeform fabrication

Three-dimensional (3-D) printing techniques were used to create lost molds for advanced inhomogeneous materials made of ceramics. The utility of this process is the ability to manipulate low-loss materials, such as alumina illustrated here, into precise, fine features as periodic macroscopic inclusions in a larger host material or air. Three periodic structures were formed using solid freeform (SFF) fabrication techniques; a two-dimensional (2-D) all-dielectric electromagnetic bandgap (EBG) substrate, a 2-D metallo-dielectric substrate filter, and a 3-D woodpile EBG structure. The design of these structures is discussed and the fabricational steps are presented in detail. This process has been utilized to develop a simple two-pole filter embedded in a substrate at 10 GHz, a single resonator at 30 GHz, and a 3-D bandgap structure from 88 to 115 GHz. The wide range of features and structures that can be accurately fabricated are highlighted.

Sintered Hydroxyapatite Latticework for Bone Substitute

Hydroxyapatite suspensions were extruded through a range of nozzles from 100 to 330 μm diameter from a stepper‐driven syringe. Regular latticework scaffolds were built by fused deposition modeling (FDM), a solid freeforming method, on a three‐axis table using 330 μm diameter filament. The scaffolds were sintered at 1250°C to 97% density retaining the hydroxyapatite crystal structure. The scaffolds were introduced to cultured human osteoblast cells and, after 48 h, the surfaces were thoroughly covered with active cells.

Indirect solid free form fabrication of local and global porous, biomimetic and composite 3D polymer-ceramic scaffolds

Precise control over scaffold material, porosity, and internal pore architecture is essential for tissue engineering. By coupling solid free form (SFF) manufacturing with conventional sponge scaffold fabrication procedures, we have developed methods for casting scaffolds that contain designed and controlled locally porous and globally porous internal architectures. These methods are compatible with numerous bioresorbable and non-resorbable polymers, ceramics, and biologic materials. Phase separation, emulsion-solvent diffusion, and porogen leaching were used to create poly( l)lactide (PLA) scaffolds containing both computationally designed global pores (500, 600, or 800 μm wide channels) and solvent fashioned local pores (50–100 μm wide voids or 5–10 μm length plates). Globally porous PLA and polyglycolide/PLA discrete composites were made using melt processing. Biphasic scaffolds with mechanically interdigitated PLA and sintered hydroxyapatite regions were fabricated with 500 and 600 μm wide global pores. PLA scaffolds with complex internal architectures that mimicked human trabecular bone were produced. Our indirect fabrication using casting in SFF molds provided enhanced control over scaffold shape, material, porosity and pore architecture, including size, geometry, orientation, branching, and interconnectivity. These scaffolds that contain concurrent local and global pores, discrete material regions, and biomimetic internal architectures may prove valuable for multi-tissue and structural tissue interface engineering.

A drop-on-demand ink-jet printer for combinatorial libraries and functionally graded ceramics.

A printer has been designed and built for the preparation of combinatorial libraries of ceramics and for solid freeforming of functionally graded ceramics with three-dimensionally programmable spatial variation in composition. Several ceramic suspensions (as inks) can be subjected to micromixing behind the nozzle and printed at precise positions. Both mixing and positioning are computer-controlled. The machine consists of an XY table to control the geometry, a set of electromagnetic valves that manage the mixing, a combined electromagnetic valve and sapphire nozzle that form the print head, and a computer that controls the whole system. The mixing valves can eject as little as 1 mg/s ink into the mixing chamber. The printer has been controlled, run, calibrated and tested; the composition and geometry of printed mixtures can be controlled precisely. This method for the controlled mixing of powders facilitates the advance of combinatorial methods within the materials sciences.

Direct ink jet printing of ceramics: experiment in teleology

AbstractThere is now more openness about the idea that instruments, machines, and processes might have different uses from those intended by the designer or maker. This could benefit both the traditional and engineering ceramics industries. The connectivity of manufacturing pathways both within and between industries is beginning to be recognised in modern approaches to processing, and this recognition facilitates exchange and innovation. The present paper describes a change of purpose for ink jet printers to provide, inter alia, a solid freeforming (SFF) pathway to make components from a computer file by deposition of a well dispersed powder in suspension. Solid freeforming is defined as the creation of a three-dimensional shape by point, line, or planar addition of material without the use of confining surfaces other than a base. It complements the categories of casting, plastic deformation, joining, and machining as a core concept in manufacturing. It has its origins in stone and brickwork. Internal ch...

Solid Freeforming of Silicon Carbide by Inkjet Printing Using a Polymeric Precursor

Preceramic polymers can be dissolved in solvents to form low‐viscosity fluids. This makes them suitable for solid freeforming by direct inkjet printing. Two ways of using polycarbosilane (pcs) were investigated. In the first, it was dissolved in n‐heptane at up to 30 vol% and printed as a single‐phase material. In the second, it was used as an organic binder for silicon carbide powder suspended in an homologous series of hydrocarbon solvents ranging from n‐heptane to n‐decane. Polyisobutene succinimide was used as a surfactant. In both cases, components could be rendered successfully but pyrolysis of the unfilled pcs resulted in cracking. Components printed with powder suspensions did not crack on pyrolysis, retained overall near net shape, and underwent low shrinkage (8.2 vol%). The molecular weight of the n‐paraffin solvents influenced the viscosity and hence the maximum powder loading while the volatility, a property also related to molecular weight, influenced the quiescence time and the drying time needed between layers. Octane gave the best compromise between speed of printing, the quality and knitting of droplet relics, and the avoidance of nozzle blockage caused by too rapid drying.

Ceramic Freeforming Using an Advanced Multinozzle Ink-Jet Printer

A high performance, multinozzle, piezoelectric drop-on-demand ink-jet printer was used for solid freeforming of ceramics by direct, multiple-layer printing of suspensions of a commercially available powder. The wide-array print head was arranged over a single-axis stepper-motor driven table. Ceramic inks were prepared using low-polarity solvents to give low-ink conductivity and, hence, prevent corrosion of the electroding system in the print head. Zirconia inks were prepared in a high-energy bead mill charged with 500 μm diameter zirconia media. The procedure for selecting solvent, dispersant, resin and their proportions is discussed in the context of print quality. The surface quality and fracture surfaces of three-dimensional (3-D) sintered zirconia test coupons were studied by microscopy. The fracture surfaces showed no sign of droplet relics and could not be used to detect the method of powder assembly.

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.

Application of a continuous ink jet printer to solid freeforming of ceramics

A continuous ink jet printer similar to the devices applied in the date-labelling of food packaging has been used for the direct freeforming of ceramics by multiple overprinting. In order to characterize the printer, ranges of test liquids were prepared to assess the effects of viscosity, surface tension and conductivity on the drop break-up and print behaviour. The printer was fitted with a 60 μm sapphire nozzle. The operating ranges of these parameters, in conjunction with the ink pressure were identified for reproducible droplet positioning and this allowed a ceramic ink to be formulated and tested.

Rapid Electroforming Tooling

AbstractA method of rapid electroforming tooling for the production of metal tools including molds, dies, and electrical discharge machining electrodes is developed. Geometry and material of the solid freeform fabricated part, properties of the electroformed metal, and process parameters are significant factors that cause inaccuracy in the manufactured tools. Thermomechanical modeling and numerical simulation are used to simulate thermal stresses induced during the burnout process that removes the rapid prototyping part from the electroform. The analysis demonstrates that appropriate design of the rapid prototyping part geometry and selection of electroform thickness not only reduce thermal stress, thus improving tooling accuracy, but also minimize manufacturing time and cost.

Gradient and Discrete Region Composites Produced by Solid Free Form Fabrication Techniques

AbstractStereolithography 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.

RSVP: a geometric toolkit for controlled repair of solid models

The paper presents a system and the associated algorithms for repairing the boundary representation of CAD models. Two types of errors are considered: topological errors, i.e., aggregate errors, like zero volume parts, duplicate or missing parts, inconsistent surface orientation, etc., and geometric errors, i.e., numerical imprecision errors, like cracks or overlaps of geometry. The output of our system describes a set of clean and consistent two-manifolds (possibly with boundaries) with derived adjacencies. Such solid representation enables the application of a variety of rendering and analysis algorithms, e.g., finite element analysis, radiosity computation, model simplification, and solid free form fabrication. The algorithms described were originally designed to correct errors in polygonal B-Reps. We also present an extension for spline surfaces. Central to our system is a procedure for inferring local adjacencies of edges. The geometric representation of topologically adjacent edges are merged to evolve a set of two-manifolds. Aggregate errors are discovered during the merging step. Unfortunately, there are many ambiguous situations where errors admit more than one valid solution. Our system proposes an object repairing process based on a set of user tunable heuristics. The system also allows the user to override the algorithm's decisions in a repair visualization step. In essence, this visualization step presents an organized and intuitive way for the user to explore the space of valid solutions and to select the correct one.

Rapid Prototyping and Solid Free Form Fabrication

This article will give a brief review of the start-of-the-art in commercial practice and advanced research in the field of Rapid Prototyping with special attention to the additive methods of Solid Free Form Fabrication. Recent applications of this technology in computer integrated manufacturing environments will be outlined. Future applications and research in new materials will also be addressed.

Development of Ceramic Inks for Jet Printing: Effect of Conductivity

Recently jet printers have been used in this laboratory for solid freeforming of ceramics. The development of ceramic inks, which are well-dispersed dilute suspensions of powder in a liquid carrier, is a critical stage of this process. The ink is put through the printer to directly print ceramic shapes. The conductivity of the ink is a crucial parameter for most jet printing operations. Several ceramic inks have been prepared and characterized. Their conductivities have been measured using a standardized cell. Several ceramic inks that can be used in direct ceramic jet printing have been developed.

Solid freeforming of ceramics using a drop-on-demand jet printer

The formulation of a stabilized ceramic ink and the adaptation of a piezoelectric-activated drop- on-demand jet printer with a 65 mm nozzle for the direct solid freeforming of ceramics by multilayer jet printing is reported. The procedure has exciting implications for the miniaturization of ceramic circuits and for the fabrication of solid oxide fuel cells, ordered ceramic composites and small monolithic ceramic components of complex shape.

Mechanical properties of dense polylactic acid structures fabricated by three dimensional printing

Polylactic acid (PLA) is a bioresorbable polymer that is used in a number of clinical situations. Complex shapes of PLA are commonly machined for bone fixation and reconstruction. Solid free form fabrication methods, such as 3D printing, can produce complex-shaped articles directly from a CAD model. This study reports on the mechanical properties of 3D-printed PLLA parts. 3D printing is a solid free-form fabrication process which produces components by ink-jet printing a binder into sequential powder layers. Test bars were fabricated from low and high molecular weight PLA powders with chloroform used as a binder. The binder printed per unit line length of the powder was varied to analyze the effects of printing conditions on mechanical and physical properties of the PLA bars. Furthermore, cold isostatic pressing was performed after printing to improve the mechanical properties of the printed bars. The maximum measured tensile strength for the low molecular weight PLLA (53 000) is 17.40 ± 0.71 MPa and for high molecular weight PLLA (312 000) is 15.94 ± 1.50 MPa.

Intelligent production technology future-oriented vision or industrial reality

The following paper is a short version of the plenary paper presented as an introduction and overview of the Conference “Intelligent Production Systems—Solid Freeform Manufacturing”. One aim is the explanation of the new epoch of advanced manufacturing technology characterized especially by the higher degree of machine intelligence. Another important aspect is the great influence of all activities in the areas of product development and manufacturing. The solid freeform manufacturing procedures are not only to be understood as some additional new manufacturing processes. Rather it is necessary to utilize all given possibilities from various user points of view.

The EOS rapid prototyping concept

The EOS rapid prototyping concept and technological state-of-the-art was presented at the Solid Freeform Manufacturing congress in Dresden in September 1994. Here the concept is discussed in more detail and the technological aspects are updated, in line with the rapid rate of development in this field. First the principle of layer manufacturing techniques (LMT) is defined and their role within the concept of rapid prototyping (RP) is explained. The individual elements of the EOS rapid prototyping concept (optical digitization, stereolithography and laser-sintering) are explained in turn, in each case with both a technical description and a discussion of the applications. A number of new developments in LMT building strategies and materials are reported, including direct sintering of metal powder.

Solid Freeform Manufacturing technologies as an important step in the product development process

Solid Freeform Manufacturing has emerged as a valuable tool for rapid prototyping. Its advantages over conventional manufacturing processes for quick product visualization enable companies to spend considerably less money and time in bringing products from the computer tube to the table top. However, to effectively utilize this manufacturing technique to its full potential, its process capabilities must be clearly understood. The constant advances in accuracies, resins, and casting techniques necessitate the requirement to have this data available for the Integrated Product Team. This paper will discuss the importance of relating process capabilities to product features and present a method for automated producibility analysis utilizing component features and process knowledge capture.