2000 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/73461

Proceedings for the 2000 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Eleventh Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 8-10, 2000, was attended by over 100 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. 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 Rosalie Foster 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 chairs, 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 (N00014-00-1-0674) and the National Science Foundation (DMI-0003777) for supporting this meeting financially. The meeting was co-organized by the University of Connecticut at Storrs, and the Mechanical Engineering Department, Laboratory for Freeform Fabrication and the Texas Materials Institute at The University of Texas at Austin.


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    2000 International Solid Freeform Fabrication Symposium Table of Contents
    (2000) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Machine Vision Based Control of Gas Tungsten Arc Welding for Rapid Prototyping 578
    (2000) Kmecko, I.S.; Kovacevic, R.; Jandric, Z.
    A machine vision system, based on CCD camera, is used to control the molten pool size during the gas tungsten arc welding (GTAW) process. The technique is tested by making a metallic part with a complex 3-D network of conformal channels on a hybrid rapid prototyping machine based on welding and milling. The test part demonstrated manufacturing flexibility and new technological opportunities required for prototyping injection mold tools. The real metallic part made in a layered fashion had good surface quality, dimensional accuracy, and high density.
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    Manufacture of Compliant Prosthesis Sockets using Selective Laser Sintering 565
    (2000) Stephens, Sean; Crawford, Richard H.; Rogers, William; Gitter, Andrew; Bosker, Gorden
    Solid Freeform Fabrication to date has largely been applied in prototype fabrication or fabrication of patterns for conventional manufacturing methods. However, many opportunities exist for using SFF for manufacturing the actual product. In particular, those applications that require or can be enhanced by custom geometric design seem to be well suited for SFF techniques. In this paper we describe the design of a prosthesis socket for a below-the-knee amputee. This socket is specifically designed to provide compliance in selected areas to enhance the comfort of the wearer. Additionally, the socket contains an integrated pylon fitting that provides a structurally superior connection while also improving the comfort of the wearer. The socket was manufactured using selective laser sintering, mated to a pylon and foot, and fitted to the patient for gait analysis. The results of the analysis indicate an improved fit is possible with manufacture by SLS.
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    Anatomical Modeling and Rapid Prototyping Assisted Surgical Reconstruction 555
    (2000) Jiang, T.; Lin, F.; Kaltman, Steven I.; Sun, W.
    A CAD-based approach to generate three-dimensional anatomical modeling and its application in analysis and rapid prototyping for surgical reconstruction is presented. The process of modeling technique, starting from processing computed tomography segmentation profiles, reverse engineering to reconstruct 3D anatomical model, and rapid prototyping to fabricate physical models are described. Methods of applying the least-square fitting criteria to simplify CT or MRI anatomical data, to generate NURBS based curves, surfaces, and solids, and to develop a CAD-based anatomical modeling for femur are introduced. Feasibility of using finite element method for femur structural analysis and using rapid prototyping to reproduce tactical medical model for surgical reconstruction is also discussed.
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    Forensic Applications of Solid Freeform Fabrication 549
    (2000) Crockett, Robert S.; Zick, Rebecca
    Solid Freeform Fabrication was recently used to identify the dismembered body of a woman found in rural Wisconsin. Skin from the face of the victim had been removed, making visual identification impossible. A model of the skull was constructed by Laminated Object Manufacturing (LOM), using data extracted from CT scans of the victim’s head. Forensic anthropologists performed a facial reconstruction directly on the LOM model, which was then photographed and distributed. The computer model was further manipulated and served as supplemental data to investigators preparing the reconstruction. An identification from one of the distributed photographs led to the arrest of a suspect and a subsequent conviction. This is the first example that we are aware of where SFF has been used in an active criminal case, and the successful results show a promising future for SFF as a forensic tool.
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    Laser Bending of Thin Metal Sheets by Means of a Low Power CO2 Laser 537
    (2000) Lubiano, Gigliola; Ramon, Jorge A.; Magee, Johnathan
    An experimental study of the deformation phenomena during laser bending of 0.5 mm metal sheets is presented here. The thermal gradient mechanism, i.e. ratio of the laser beam diameter to the sheet thickness less than unity, was used to bend the samples. The sheets, which are made of 304 stainless steel, 1100 aluminum and 1010 carbon steel, were scanned with a focused CO2 laser beam for several times. Optical power of the laser ranged from 64 to 95 W and its maximum traverse speed was 15 mm/s. Results are presented as plots of the bending angle vs. number of scans (i.e. 2θ-N curves). Understanding of this novel forming process is crucial in order to find applications for it in the rapid prototyping field.
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    Advanced Sheet Metal Manufacturing using Rapid Tooling 522
    (2000) Hui, Du Zhao; Kai, Chua Chee; Sen, Chua Yew; Gek, Loh-Lee Keow; Tiak, Lim Ser
    A closed loop process is proposed for making sheet metal prototyping parts by using advanced computer aided techniques and computer controlled machines. The key aspect of this process is the method used to fabricate and modify the sheet metal forming tools, which are not necessarily for mass production but should be suitable for short run production or design evaluation of sheet metal products where the prototyping cost and lead-time are greatly reduced. Various approaches are investigated in the preparation of the tooling for onward embossing on a sheet metal. The three indirect approaches use Selective Laser Sintering (SLS), Stereolithography(SLA), and high speed Computer Numerical Controlled (CNC) milling to build the masters from computer data models. And the masters are then served in the vacuum casting process to generate the non-ferrous tooling. The direct approach uses DTM’s RapidSteel to produce the metal tooling without going through any secondary process. Comparisons on quality, leading time and cost are presented.
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    Determination and Improvement of Building Speed in Rapid Freeze Prototyping 514
    (2000) Zhang, Wei; Sui, Guanghua; Leu, Ming C.
    Rapid freeze prototyping (RFP) is a solid freeform fabrication process that builds an ice part by rapidly freezing water in a layer by layer manner. One advantage of this process is the ability to build ice parts faster than other SFF processes. The factors that affect the speed of contour building and interior filling in RFP are identified. The influence of these factors is analyzed through heat transfer and material flow analyses. A model based on heat transfer analysis is proposed to determine the maximum achievable speed of contour building under stable conditions. Experiments are conducted to validate the performance of the proposed model for determination of building speed.
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    Indirect Rapid Molds for Prototype Lost-Foam Pattern Production 506
    (2000) Gervasi, Vito R.; Shaikh, F. Zafar
    Lost-foam (also known as Expendable Pattern Casting, EPC) is an ever-growing metalmcasting technique, capable of producing complex metal components without parting lines. Mold preparation for lost-foam casting is typically accurate, but expensive and slow. The goal of this research was to develop a new approach for producing rapid lost-foam molds. With this new approach, patterns generated by SFF technology are used to form indirect composite lost-foam molds. Ultimately, our objective is to produce these molds quickly, accurately, and inexpensively. This new approach to lost-foam mold-making will be explained as well as the results of one trial.
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    Fabrication of Advanced Thermionic Emitters Using Laser Chemical Vapor Deposition-Rapid Prototyping 498
    (2000) Fuhrman, Brian T.; Duty, Chad E.; Jean, Daniel L.; Lackey, W. Jack
    Laser Chemical Vapor Deposition-Rapid Prototyping (LCVD-RP) is a relatively new manufacturing process. Its capabilities are ideally suited for the manufacturing of a type of electron emitter called an integrated-grid thermionic emitter. The integrated-grid thermionic emitter is composed of wagon wheel-like structures of alternating layers of boron nitride and molybdenum on tungsten. The goal of this paper is to determine the feasibility of using LCVDRP technology to manufacture advanced thermionic emitters.
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    Conformal Cooling and Heating Channels using Laser Sintered Tools 490
    (2000) Hopkinson, Neil; Dickens, Phill
    The EOS Direct Metal Laser Sintering (DMLS) and DTM Rapid Steel 2 processes may be used to create tools incorporating conformal channels behind the tool surface through which fluids may be passed. To date, a significant amount of work has been carried out to investigate the efficiency of using conformal channels to cool tools. This work suggests the use of conformal channels to both cool and heat a single tool. This may appear self-defeating at first but the selective nature by which conformal channels may make this a worthwhile means of generating hitherto unavailable thermal conditions within a tool. Such conditions may then allow the successful production of geometries which had previously been impossible to mould.
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    The Selection of Mould Design Variables in Direct Stereolithography Injection Mould Tooling 478
    (2000) Harris, Russ; Hopkinson, Neil; Dickens, Phill; Hague, Richard
    The introduction of rapid prototyping has allowed engineers and designers to generate physical models of required parts very early on in the design and development phase. Further to this the use of stereolithography (SL) cavities as a rapid tooling method has allowed plastic prototype parts to be produced in their most common production manner; by injection moulding. The process is best suited to small production runs where the high costs of conventionally machined tooling is prohibitive. One of the major drawbacks of the SL injection moulding process is the susceptibility of the tools to premature failure. SL tools may break under the force exerted by part ejection when the friction between a moulding and a core is greater than the tensile strength of the core resulting in tensile failure. Very few justified recommendations exist concerning the choice of mould design variables that can lower the part ejection force experienced and reduce the risk of SL tool failure. This research investigates the ejection forces resulting from injection moulding polypropylene (PP) and acrylonitrile-butadiene-styrene (ABS) parts from SL tools which are identical in all respects except for their build layer thickness and incorporated draft angles. This work attempts to identify appropriate evidence for recommendations with respect to these design variables and SL injection moulding. The results show that adjustment of draft angle results in a change of part ejection force as a reasonably linear relationship. An adjustment of the build layer thickness results in a change in part ejection force as a more non-linear relationship. The adjustment of build layer thickness had a greater effect on ejection force than the adjustment of draft angle. In both cases greater ejection forces were experienced by ABS parts as compared to PP parts. The results also show that the surface roughness of all tools remains unchanged after moulding a number of parts in both polymers.
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    Relationships Between Wall Thickness and Erosion Depth of Thin Walled Electroformed EDM Electrodes Produced From RP Models 469
    (2000) Bocking, Chris; Rennie, Allan E. W.; Bennett, G.R.
    Metal filled thin walled electroformed EDM electrodes, fabricated using RP models, have been shown to be an effective route to producing die sink electrodes. However, due to the nature of electroforming, there are certain limits to the maximum depth of erosion of cavities that can be achieved, this being related to the electrode wall thickness. This initial study examines the relationship between the electrode wall thickness and depth of erosion.
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    Heat Transfer Analysis of a Gas-Jet Laser Chemical Vapor Deposition (LCVD) Process 461
    (2000) Duty, Chad E.; Fuhrman, Brian T.; Jean, Daniel L.; Lackey, W. Jack
    This paper describes the development of a computer model used to characterize the heat transfer properties of a gas-jet LCVD process. A commercial software package was used to combine heat transfer finite element analysis with the capabilities of computational fluid dynamic software (CFDS). Such a model is able to account for both conduction and forced convection modes of heat transfer. The maximum substrate temperature was studied as a function of laser power and gas-jet velocity.
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    Laser Penetration in a Powder Bed During Selective Laser Sintering of Metal Powders: Simulations Versus Experiments 453
    (2000) Laoui, Tahar; Wang, Xiaochuan; Childs, T.H.C.; Kruth, Jean-Pierre; Froyen, Ludo
    To gain a better understanding and control of the Selective Laser Sintering (SLS) process, more fundamental and modeling work is needed. A simple analytical ray-tracing model has been developed to simulate the energy absorption and penetration in SLS. The model is applied to FeCu and WC-Co powder mixtures, irradiated by Nd-YAG or CO2 laser. It gives an evaluation of the total energy incoupling and optical penetration of the laser beam in a powder bed and an estimation of the sintering zone dimensions. Another model, which considers heat flow by conduction in the bed, has also been used to estimate the sintering dimensions of one laser track.
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    Tool Path Generation for Flexible Blade Cutting
    (2000) Broek, Han J.; Horváth, Imre; Smit, Bram de
    Free Form Thick Layered Object Manufacturing FF-TLOM is based on application of a reshapeable cutting device, which allows a free form shaping of thick polystyrene foam layers. Once manufactured, these layers are stacked to produce a physical model. Tool path generation for the heated flexible blade tool is a challenging task, since it influences the quality of the manufactured objects as well as the effectiveness of the fabrication process. Them difficulties arise from the following facts: (a) when slicing is computed, the instantaneous tool positions are defined by matching the blade profile against the nominal shape of the CAD model, (b) the tool positions calculated relative to the cut layers have to be converted into the global reference frame of the layer cutting equipment, (c) the resultant tool path should maintain the achieved preciseness approximating the front surface of the layers, and (d) it is impossible to calculate all points of the tool path in real time. This paper proposes an effective tool path calculation method for flexible blade cutting. The contour of the layers is converted into an ordered set of smooth and awkward boundary features. For the smooth boundary features, the tool positions are computed by dense sampling in order to achieve the optimal cutting.
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    Visualization Tools for Design Support in SFF 437
    (2000) Campbell, R. Ian; Jee, Haeseong J.; Lee, H.S.
    When considering the use of SFF, there are many questions a designer might ask. What model orientation should be used, will the model have adequate aesthetic and functional properties, is the STL file suitable for transfer to the SFF machine? These questions could be answered by a comprehensive design support system for SFF. This paper addresses a number of components for such a system that can be met through the use of visualization tools. These include: 1. Visualization of surface roughness 2. Visualization of characteristic features (e.g. surface macro-texture) 3. Visual simulation of fabrication Example applications of these tools are presented together with a status review of their implementation to date. It is envisaged that these tools will be incorporated into an already existing network-based preprocessor used for visualization, repair and slicing of STL files. The direction of future work is also discussed which will include the visual representation of functionally graded materials (connected with FEM results).
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    Designing and Slicing Heterogeneous Components for Rapid Prototyping 428
    (2000) kumar, Ashok V.; Lee, Jongho
    Many rapid prototyping techniques have the potential for fabricating components whose composition is non-uniform and varies in a desired fashion. A shape and composition modeling technique was developed to enable the representation and design of such heterogeneous components. Techniques for interactively and automatically designing such components are presented. Automatic design is made possible using optimization techniques where the optimal composition distribution is computed based on specified design objective and constraints. Software was also developed to slice 3D heterogeneous solids to generate cross-sectional images as well as composition distribution for each cross-section. Slicing and generation of cross-sectional data are essential to enable rapid prototyping of these components.
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    Reasoning Boolean Operation for Modeling, Simulation and Fabrication of Heterogeneous Objects 417
    (2000) Hu, X.; Jiang, T.; Lin, F.; Sun, W.
    An approach using reasoning Boolean operation to model heterogeneous object is presented. Algorithm in the reasoning Boolean operation consists of merging and extraction operation. This algorithm models heterogeneous object at multi-volume level. Due to its CAD-based nature, the model can be implemented with advanced CAD/CAE/CAM software for integrated design, simulation, and prototyping fabrication. Example of using the developed modeling technique to construct the heterogeneous composite unit cells, to perform integrated design and analysis, and to develop a pseudo-processing algorithm for layered fabrication of heterogeneous object is also presented.
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    Model-Based Control of Cure Distribution in Polymer Composite Parts Made by Laminated Object Fabrication (LOF) 409
    (2000) Klosterman, Donald; Chartoff, Richard; Flach, Lawrance; Bryant, Eric
    A mathematical heat transfer model was used to investigate process control strategies for making thermoset polymer composite materials by Laminated Object Fabrication (LOF). The temperature of the laminator was manipulated in order to control the uniformity and overall level of cure through the thickness of a 20-layer part. When the laminator temperature was held constant throughout the LOF build process, as is normally the case in practice, the model predicted that the resulting panel would have a steep cure gradient from top to bottom. This was considered to be undesirable. The model was then used in conjunction with an optimization algorithm to determine a temperature program for the laminator which would result in panels with a more desirable spatial cure profile (i.e. constant). Computer model simulations demonstrated that it should be feasible to control both the level and distribution of cure in thermoset composite panels layed-up with LOF by simply manipulating the laminator temperature with simple and realistic heating schedules.