1998 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/69899

Proceedings for the 1998 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Ninth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 10- 12, 1998, was attended by over 150 national and international researchers. Papers addressed SFF issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. New sessions on ceramic materials and multiple materials SFF were added to this year's program. The diverse domestic and foreign attendees included industrial users, SFF machine manufacturers, university researchers and representatives from the government. We are pleased once again with the strong showing of university students. The excitement generated at the Symposium reflects the participants' total involvement in SFF and the future technical health of this growing technology. The Symposium organizers look forward to its being a continuing forum for technical exchange among the expanding body of researchers involved in SFF.

The Symposium was again organized in a manner to allow the multi-disciplinary nature of the SFF research to be presented coherently, with various sessions emphasizing computer issues, machine topics, and the variety of materials aspects of SFF. We believe that documenting the changing state of SFF art as represented by these Proceedings will serve both the people presently involved in this fruitful technical area as well as new researchers and users entering the field.

The editors would like to extend a warm "Thank You" to Glorya Gutchess for her detailed handling of the logistics of the meeting and the Proceedings, as well as her excellent performance as registrar and problem solver during the meeting. We would like to thank the organizing committee, the session chairmen, the attendees for their enthusiastic contributions, and the speakers both for their significant contribution to the meeting and for the relatively prompt delivery of the manuscripts comprising this volume. We look forward to the continued close cooperation of the SFF community in organizing the Symposium. We also want to thank the Office of Naval Research (Grant No. NO00 14-96- 1-044 1) and the National Science Foundation (Grant DM- 98 12084) for supporting this meeting financially. Other co-sponsors included DARPA, The Rapid Prototyping Association of the Society of Manufacturing Engineers, The Minerals, Metals and Materials Society, and the University of Connecticut at Storrs along with the Mechanical Engineering Department, Laboratory for Freeform Fabrication and the Texas Materials Institute at The University of Texas at Austin.


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    1998 International Solid Freeform Fabrication Symposium Table of Contents
    (1998) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Net Shape Fabrication of SiC and SiC/SiC Components Using Laminated Object Manufacturing (LaM): Overall Process Flowchart
    (1998) Klosterman, Don; Chartoff, Richard; Osborne, Nora; Graves, George; Lightman, Allan; Bezeredi, Akos
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    Properties of a High Temperature Liquid Crystal Stereolithography Resin
    (1998) Chartoff, R.P.; Schultz, J.W.; Bhatt, J.; Ullett, J.S.
    A liquid crystal monomer has been developed that contains both acrylate and acetylene reactive groups. The curing behavior and mechanical properties ofthe polymers formed from this monomer have been characterized in this study. Complete cure can be carried out in two separate steps, combining both photo and thermal polymerization. The initial photo- polymerization to form a robust "green" polymer involves crosslinking through the acrylate groups and the subsequent thermal polymerization to increase the crosslink density is accomplished by reaction of the acetylene groups. After the thermal postcure the polymer has an unusually high glass transition, in excess of 300°C. In addition, the monomer exhibits an ordered liquid crystalline (LC) phase. Photopolymerization while in the LC phase locks in the molecular ordering. Mechanical property data and additional information on curing in both the isotropic and LC phases are reviewed in the following presentation.
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    Composites with Gradient Properties From Solid Freeform Fabrication
    (1998) Gervasi, V.R.; Crockett, R.S.
    TetraCast is a build style developed by Milwaukee School ofEngineering involving stereolithography patterns produced with an open cellular structure inside a surface shell. Composites are created using this pattern as a host fora filler material, generally epoxy matrices loaded with various fibers or microspheres. Regions within a singleobjectrrray be separated by thin barriers, allowing filling with different matrix materials.to create regiollsof differing.local properties. The internal structure can also be continually graded in thickness to prodUl::e composites with properties ranging from that ofthe fillermaterial to that ofthe TetraCast material (currently stereolithography epoxy or FDM ABS)
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    Automated Fabrication of Complex Molded Parts Using Mold SOM
    (1998) Cooper, A.G.; Kang, S.; Kietzman, J.W.; Prinz, F.B.; Lombardi, J.L.; Weiss, L.
    Mold Shape Deposition Manufacturing (Mold SDM) is a Solid Freeform Fabrication technique for producing complex shaped fugitive wax molds. A vari~ty of castable. polymer and ceramic materials have been used to make parts from these molds. ThIS paper descnbes the Mold SDM method and an automated mold building machine based on a commercial CNC mill. Process steps, material selection and equipment issues are explained. Alumina, silicon nitride, polyurethane and epoxy parts with feature sizes ranging from 0.5 to 30 mm will be shown, as well as preassembled mechanisms and multi-material parts.
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    Fabrication of Curved Ceramic / Polymer Composite Transducers for Ultrasonic Imaging Applications by Fused Deposition of Ceramics
    (1998) Lous, G.M.; Cornejo, I.A.; McNulty, T.F.; Safari, A.; Danforth, S.C.
    Fused Deposition of Ceramics (FDC), developed at Rutgers University, is a Solid Freeform Fabrication (SFF) technique where a three-dimensional green ceramic object is built layer by layer, starting from a Computer Aided Design (CAD) file of the object. This technique was used to build novel piezoelectric ultrasonic transducers for medical imaging applications. Curved ceramic skeletons for 2-2 (parallel ceramic / epoxy plates) composite transducers were built by FDC. The design's curvature can be tailored in the CAD file. Therefore, the final composite requires very little machining. In the FDC-built green parts, the ceramic plates were 500 um thick and the spacing between the plates was 1270 um. The FDC green samples were subjected to a slow binder burnout cycle at 550°C for 4 hours, using a heating rate of 8°C per hour, then sintered at 1285°C for 1 hour. Physical characterization of the samples revealed that 95% ofthe theoretical density was achieved. The ceramic plates shrunk 20% in height as well as in width. The shrinkage was of only 16% in the direction parallel to the plates. Optical microscopy and SEM were performed on green and sintered samples. The results of these characterizations are reported in this paper as well as the electromechanical properties of the final composites and of FDC bulk samples.
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    Functionally Optimized Ceramic Structures
    (1998) Gasdaska, C.; Clancy, R.; Ortiz, M.; Jamalabad, V.; Virkar, Anil; Popovitch, Dragan
    The feasibility of using the Fused Deposition of Ceramics (FDC) process to rapidly fabricate functional quality advanced ceramic components has been demonstrated multiple extrusion heads enable the deposition of spatially engineered ceramic microstructures on the scale of 250 um. This unique capability of FDC allows components to be built with combinations of materials and properties that are difficult or impossible to produce using conventional fabrication processes. Some concepts will be presented, along with examples of multiple material laminates produced using FDC. Strength data will be presented which demonstrates the performance improvement possible using spatially engineered microstructures.
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    Recent Developments in Robocasting of Ceramics and Multimaterial Deposition
    (1998) Cesarano Ill, Joseph; King, Bruce H.; Denham, Hugh B.
    Robocasting is a freeform fabrication technique for dense ceramics and composites that is based on layer-wise deposition of highly loaded colloidalslurries. 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 overview will highlight recent 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.
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    Features in Layered Manufacturing of Heterogeneous Objects
    (1998) Qian, Xiaoping; Dutta, Debasish
    The usage of features in computer aided design and manufacturing has increased significantly over the last decade. By and large, all such features are geometric (form features). In this paper, we shall discuss the need to go beyond current geometric features and consider material -- composition, and gradation -- within the object. This need has been brought about by layered manufacturing technologies which build up parts, layer by layer, under computer control. While industrial use of this new technology has been for making prototypes, functional metallic parts can/are being made by layered manufacturing. Furthermore, a variety of materials can be deposited to create multi-material and functionally graded components. We consider features in this new domain (of layered manufacturing) and identify research topics and present an overview of our current focus on "material features" in the context of heterogeneous solid models.
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    Virtual Simulation for Multi-material LM Process
    (1998) Qiu, Dan; Langrana, Noshir A.; Danforth, Stephen C.; Safar, Ahmad; Jafar, Mohsen
    In an ONR funded MURI program, to improve quality of multi-material parts, we've been developing an advanced computer simulation for the multi-material layered manufacturing (LM) process. The CAD models and their .stLfiles are created using. the commercially available software such as I-DEAS and ProE. Using this information, one tool path file per material is generated. Our file preparation algorithm, systematically, layer by layer, integrates all tool path files into one multi-material tool path file. The results of the multi-material tool path are graphically visualized using the simulation algorithm (written in c++ & SGI OpenGL). From a virtual simulation, we can check the LM process, and make the best selection of tool path parameters afterwards. After several trials from design to simulation, if the simulation result is acceptable, the real manufacturing can be started. And the part's quality should be better than a part manufactured without running simulation in advance. This paper will represent .•. new studies on using real toadshapes to get more realistic simulation results. Many parts have been successfully simulated using our method.
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    Curved Layer LOM of Ceramics and Composites
    (1998) Klosterman, Donald A.; Chartoff, Richard P.; Osborne, Nora R.; Graves, George A.; Lightman, Allan; Han, Gyoowan; Bezeredi, Akos; Rodrigues, Stan
    A novel rapidprototyping (RP) technology incorporating a curved layer building style has been developed. The new process,based on Laminated Object Manufacturing (LOM), is suited for efficient fabrication of curved layer structures made from ceramics and fibrous composites. Anew LOM machine was developedithatuses ceramic tapes and fiberprepregs as a feedstock and outputs at11fee dimensional green form. The green ceramic is then processed to a seamless, fully dense ceramic structure using traditional ceramic techniques. Thisreport summarizes the new LOM process. and necessary hardware. Also reviewed is the development of ceramic preforms and accompanying process technology for net shape fabrication of ceramic matrix composites (CMCs). Compared to making curved objeds with the standard flat.layer LOMprocess, the curved process affordsthe advantages of eliminated stair-step effect,increased build speed, reduced waste,reduced need for decubing, and the ability to maintain continuous fibers in the direction of curvature.
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    Binder Formulation in EVA-wax system for Fused Deposition of Ceramics
    (1998) Pekin, Senol; Zangvil, Avigdor; Ellingson, William
    Blends in the ethylene vinyl acetate (EVA) - wax system have been evaluated as potential binders.to be used in fused deposition of ceramics (FDC). In order to obtain good handling strength, it was indicated that the melting point of the polymer needs to be lower than that of the wax. In this context, it was shown that the melting point of the EVA decreases as the vinyl acetate content in the copolymer increases. By measuring the viscosity as a macroscopic property, it was shown that 20 % vinyl acetate-containing EVA is miscible in microcrystalline wax up to, atleast, 30 %.Binders used in FDC need to have low viscosity and it was pointed out that the slumping can be one main problem associated with binders with low viscosity. Thus, thermolysis of wax at low temperature is suggested as a solution. The volumetric thermal expansion and melt strength of an EVA-wax blend were displayed as a function of temperature, in the form of a penetration test.
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    A Study on Weight Loss Rate Controlled Binder Removal From Parts Produced by FDC
    (1998) Pekin, Senol; Bukowski, John; Zangvil, Avigdor
    The binder removal schedule of a binder in the ethylene vinyl acetate-wax system was analyzed by automatically adjusting the soaking duration based on the monitored weight loss of the polymer. The thermolysis of several grades of microcrystalline wax and ethylene vinyl acetate have been analyzed by TvA and DSC to support the explanation of the weight loss rate controlled binder removal experiments. During the thermolysis ofsuch binders in air, the degradation sequence is degradation and evaporation of hydrocarbons, degradation ofthe vinyl acetate, and degradation of the ethylene chain, all oxygen assisted. It was shown that the extent and the rate of the vinyl acetate degradation in air is determined by the molecular weight of the EVA, unlike its degradation in N2• It was concluded that thermolysis of light polymers is easier than that ofthe heavy ones and weight loss rate controlled binder removal technique can help in the optimization of binder removal schedule for a variety of polymers.
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    Generation of Porous Structures Using Fused Deposition
    (1998) Bertoldi, M.; Yardimci, M. A; Pistor, C. M; Guceri, S.I; Danforth, S. C.
    The Fused Deposition Modeling process uses hardware and software machine-level language that are very similar to that of a pen-plotter. Consequently, the·use of patterns with poly-lines as basic geometric features, instead of the current method based on filled polygons (monolithic models), can increase its efficiency. In the current study, various toolpath planning methods have been developed to fabricate porous structures. Computational domain decomposition methods can be applied to the physical or to slice-level domains to generate structured and unstructured grids. Also, textures can be created using periodic tiling of the layer with unit cells (squares, honeycombs, etc). Methods 'based on curves include fractal space filling curves and.change of effective road width Within a layer or within a continuous curve. Individual phases can also be placed in binary compositions. In present investigation, a custom software has been developed and implemented to generate build files (SML) and slice files (SSL) for the above-mentioned structures, demonstrating the efficient control ofthe size, shape, and distribution ofporosity.
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    Automated Fabrication of Nonresorbable Bone Implants Using Laminated Object Manufacturing (LOM)
    (1998) Steidle, Cheri; Klosterman, Don; Osborne, Nora; Graves, George; Chartoff, Richard
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    Processing of Bioceramic Implants Via Fused Deposition Process
    (1998) Bose, Susmita; Avila, Marisol; Bandyopadhyay, Amit
    Porous ceramic structures have long been a subject of investigation as bone sl..bstitute. Most of these porous structures are typically made by techniques that result .randomly arranged pores with a wide variety of pore sizes. In recent years, SFF methods are being used for the fabrication of porous bioceramic implants. Porous ceramic structures have been fabricated using indirect route where a .polymeric mold is fitst created via fused deposition process. The mold was then infiltrated with ceramic slurry, dried. and ·then subjected to a binder bum out and sintering cycle. In this paper, processing of 3D honeycomb porous alumina ceramic structures and some.initial mechanical properties for bone implants will be discussed.
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    Materials for Biomedical Applications
    (1998) Barlow, J. W; Lee, G.; Aufdemorte, T. B.; Fox, W. C; Swain, L.D.; Vail, N.K
    This paper discusses two ceramic material systems for selective laser sintering (SLS) that are being developed for biomedical applications for use in repair of bone defects. SLS is the preferred method of fabricating ceramic implants that exhibit well defined porous microstructures. Implants fabricated in this. manner have proven effective in-vivo showing excellent biocompatibility as well as considerable osseous integration and remodeling of the imp'ant material
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    Development of a Binder Formulation for Fused Deposition of Ceramics
    (1998) McNulty, Thomas F.; Cornejo, Ivan; Mohammadi, Farhad; Danforth, Stephen C.; Safari, Ahmad
    A new binder formulation has been developed for Fused Deposition of Ceramics (FDC) which consists of commercially-available polymer constituents.. This formulation was used. in conjunction with lead zirconate titanate (PZT) and hydroxyapatite (HAp) powders. Adsorption studies were performed to test the effectiveness of several carboxylic acids and alcohols on the dispersion ofthese powders in the binder system. In both cases, it was found that stearic acid was most effective as a dispersant for the ceramic powder / thermoplastic system. After a suitable dispersant was chosen, ceramic powders were compounded with the binder formulation to yield 55 vol.% ceramic-loaded materials. The resultant compound was·used to make filament suitable for use in a modified StratasysTM 3D-Modeler. The filament was well suited for FDC usage, and the parts made using FDC contained no detectable filament-related defects
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    Selective Laser Sintering of Zirconium Silicate
    (1998) Klocke, F.; Wirtz, H.
    The Fraunhofer Institute of Production Technology (IPT) and the Fraunhofer Institute of Laser Technology (ILT) have joined forces in a project dedicated to Selective Laser Sintering (SLS) ofmetals and ceramics, funded by the German Government and 6 industrial partners. Selective Laser Sintering of zirconium silicate as a ceramic material used for investment casting shells and cores is an attractive alternative to the conventional, time-consuming way of producing these shells from a wax master. This paper will present current process results concerning laser sintering of shells made from zirconium silicate and explain the related potentials and benefits.
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    Titanium Casting Molds via Selective Laser Sintering
    (1998) Harlan, Nicole; Bourell, David; Beaman, Joe
    A mold material system has been developed that can be SLS processed and used to cast titanium alloys. Stabilized zirconia, chosen forits low reactivity with molten titanium, has been sintered into mold shapes. The molds have been infiltrated with a colloidal solution ofunstabilized zirconia and fired to create a partially stabilized structure. ·SEM analysis shows that the unstabilized zirconia forms bridges between the larger stabilized zirconia particles that provide strength to the mold.