2001 International Solid Freeform Fabrication Symposium

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Proceedings for the 2001 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Twelfth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 6-8, 2001, was attended by over 130 national and international researchers. Papers addressed SFF issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. 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.

A special plenary session on the state of SFF was organized to present overview talks on various aspects of the field. Invited speakers were Joseph Beaman (University of Texas) who gave a historical perspective, Emanuel Sachs (MIT) who related SFF to manufacturing, Phill Dickens (DeMontfort University) who gave a presentation on the role of SFF in design, Kevin Lyons (NIST) who spoke on software developments and Fritz Prinz (Stanford) who discussed the future of 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 modeling, process development, and materials. We believe that documenting the changing state of SFF art as represented by these Proceedings will serve both those 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 (N00014-01-1-0637) and the National Science Foundation (DMI-0117072) 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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    2001 International Solid Freeform Fabrication Symposium Table of Contents
    (2001) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Laser Fusion Coatings of Functional Parts
    (2001) Ramos, J.A.; Bourell, D.L.; Govindaraju, M.R.
    Surface characteristics of functional parts made by Solid Freeform Fabrication techniques such as Selective Laser Sintering (SLS), Stereolitography Apparatus (SLA) or other fabrication techniques can be enhanced by the application of multi-element based laser fused coatings. Environmental protection and wear resistance, among other properties can be achieved by pre-depositing a slurry over the surface of the parts, followed by a high-speed scanning with a high power laser beam. Wetting of the part surface by the molten slurry is a main concern in this coating process. Wetting characteristics of molten slurry can be improved by the right combination of coating constituents, laser processing atmosphere, and laser processing parameters. Coating quality is also a critical issue to ensure good performance of the coatings especially for environmental protection. This paper presents results obtained for carbon-carbon composites coated with silicon-based slurries by laser fusion process. Criterion in selecting the coating constituents, laser process conditions, and oxidation test results are discussed.
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    Integration of Solid Freeform Fabrication in Design
    (2001) Hague, R.; Campbell, I.; Dickens, P.; Reeves, P.
    During the last few decades, designers have been educated to develop designs with restricted geometry so that parts can be made easily. The revolutionary aspect of Rapid Manufacturing will be that geometry will no longer be a limiting factor. The introduction of Rapid Manufacturing will have a number of effects on Design. It will be possible to have re-entrant shapes without complicating manufacturing, no draft angles, variable wall thickness, no split lines and fewer parts leading to easier assembly and lower stock. The individual designer’s method of working will change with the introduction of Rapid Manufacturing and also there will be changes to the overall design process. Examples will be the elimination of prototype and pre-production stages, as end part manufacture will occur as soon as the CAD is finished. This will affect project management practices and sign-off procedures.
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    Manufacturing by Solid Freeform Fabrication
    (2001) Sachs, Emanuel
    The SFF/RP industry has grown steadily with the most significant gains made in the number of models produced per year – three million in the year 2000. Future growth is most likely to be in manufacturing applications of SFF where even a single application can double the number of models/parts produced annually. There are a number of factors or drivers which can motivate a manufacturing application of SFF either individually or in combination. These drivers include: i. avoid conventional tooling, ii. minimizing hand work, iii. mass customization, iv. geometric flexibility, v. local control of composition. The most intriguing of these drivers is that of mass customization – the manufacture of highly individual products, but on a mass scale. SFF offers the possibility of mass customization of components with complex 3D geometry. A prominent current example is that of Align Technology of Santa Clara, CA which produces unique plastic aligners for orthodontic applications. There already are manufacturing applications where the advantages offered by SFF are so compelling as to overcome any barriers. However, widespread impact of SFF on manufacturing will depend on overcoming several barriers. The essence of these barriers lies in the distinction between prototyping and manufacturing. Manufacturing applications are far more demanding in terms of build rate and associated cost, demands on dimensional control and tolerances, properties of materials, and ease of use and serviceability of equipment.
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    Applications of Solid Freeform Fabrication at the Naval Research Laboratory
    (2001) Thomas, J.P.; Bender, B.A.; Pique, A.; Cooper, K.P.; Rayne, R.J.; Richardson, A.C.
    Solid Freeform Fabrication (SFF) and related techniques are used at the Naval Research Laboratory (NRL) for a variety of materials related investigations. Research and applications conducted over the past few years are described including: Helisys Laminated Object Manufacturing System (LOMS) fabrication of: ceramic piezoelectric actuators, tooling for multifunctional materials, and anatomical prototypes for surgical visualization; fabrication of mesoscale electronic and sensor components using a laser forward transfer direct write technique; and visualization of complex, 3-D microstructures using a Stratasys Fused-Deposition Modeler. The paper closes with a brief overview of future SFF related work at the NRL.
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    Synthesis of a Compact Tetralattice Heat Exchanger using Solid Freeform Fabrication and Comparison Testing Against a Tube Heat Exchanger
    (2001) Heidrich, James R.; Gervasi, Vito; Kumpaty, Subha
    The challenge for Solid Freeform Fabrication (SFF) lies in fabricating complex parts that are not possible by conventional manufacturing means. The goal was to apply SFF techniques to complex geometry heat exchangers. The heat exchanger structure is modeled after the covalently bonded carbon atoms of a diamond. The tetrahedron diamond lattice, or Tetralattice, is a repeating lattice unit that forms a network of channels to form the heat exchanger. Electroforming methods creating Tetralattice were applied to synthesize an air-oil compact heat exchanger. After production, the heat exchanger was tested and compared with an industry standard heat exchanger for performance evaluation.
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    Robocasting Periodic Lattices for Advanced Filtration
    (2001) Stuecker, John N.; Cesarano III, Joseph; Smay, James E.
    Ceramic filters used in the casting of molten metals are commonly created by slurry impregnation of polymeric foams, yielding a fired ceramic foam structure. These foam structures have high part-to-part standard deviation in flow rates (~25%) and have weak sections which can fragment into the melt. In contrast, periodic lattice filters (PLF’s) made by robocasting have a cross-hatched face-centered-cubic arrangement of rods.. As such, the robocast filters have high strength and may be easily tailored to offer a specific internal pore structure to control the flow rate and pressure drop across the filters. Standard deviation of flow rates among PLF’s are less than 1%. This paper describes the methodology of creating PLF’s as possible foam filter replacements.
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    Manufacturing of a Heterogeneous Flywheel on a LENS Apparatus
    (2001) Morvan, Stephane; Fadel, Georges; Love, James; Keicher, Dave
    The design of a 1D gradient component satisfying a particular set of constraints is extended to its manufacturing on a multi-material capable apparatus. The geometry and composition of this flywheel were designed to meet a bi-objective optimum featuring maximum kinetic energy storage and minimal maximum von-Mises stress along its radius. The efforts expanded during the transformation of this design from a computer abstraction into a tangible object are presented. The process-planning step of the manufacturing of this heterogeneous solid, which was dependent on the specifics of a LENS-based Apparatus, required a different approach than that of traditional solids, and proved critical during fabrication.
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    Powder Delivery in Dental Restoration Rapid Prototyping Process
    (2001) Wang, Jiwen; Li, Xiaoxuan; Shaw, Leon L.; Marcus, Harris L.; Cameron, Thomas B.
    Rapid prototyping of dental restoration has been investigated for its potential to save time and cost. In this paper, a powder delivery system was developed to deliver dental porcelain powder accurately into 2-D shapes for dental restoration. Aqueous suspension of the porcelain was prepared as the vehicle for the powder delivery. An integrated dry and wet ball-milling process was developed to reduce the particle size and minimize agglomeration. The reduction in particle size and minimization of agglomeration increased the suspension stability. The optimization of the pH value of the suspension also provided an additional means to achieve the stability and reduce the viscosity of the suspension. With the optimization of the particle size, pH value and solid concentration in the suspension, desired powder shapes were successfully delivered.
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    Custom Fabrication of Hard Tissue Reconstructive Frameworks
    (2001) Nambiar, R.V.; Jones, R.E.; Gomez, J.R.
    The feasibility of fabricating custom frameworks for tissue regeneration utilizing three-dimensional inkjet printing technology followed by slip casting was investigated. A CAD solid model of mold was created with structures within the mold cavity to provide variable, customized porosity in the cast framework. The polymer mold was printed using a 3D ink-jet printer. The mold was then infiltrated by an aqueous suspension of hydroxyapatite to produce porous frameworks that were tested for mechanical properties.
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    Rapid Prototyping Assisted Design and Development of Inter-Vertebral Implants
    (2001) Chiang, J.; Lehmicke, M.; Dcosta, D.; Xu, X.; Lin, F.; Sun, W.
    This paper presents a case study of applying rapid prototyping in assisting in the design and development of inter-vertebral implants for spine fusions. The major process of design and implant development, its biological and mechanical requirements, the approach for developing a 3D reconstructive vertebral anatomy model, the inter-vertebral implant CAD model, and the integration with a finite element analysis for the implant's structural analysis are presented. The process of 3D Printing of the vertebral anatomy and the inter-vertebral implant is described. The application of the prototyping model in assisting in the inter-vertebral anatomic fitting, in guiding the implant's geometric design, in helping with the virtual surgical planning, and in understanding the implant's mechanical properties and structural stability are discussed.
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    Testing of Compliance in a Prosthetic Socket Fabricated Using Selective Laser Sintering
    (2001) Lokhande, Mahendra; Crawford, Richard
    Solid freeform fabrication techniques offer potential as manufacturing technologies in applications that require custom design. One such application is the fabrication of prosthetic sockets. This paper reports on research to manufacture compliant below-the-knee prosthetic sockets using selective laser sintering (SLS). Compliance in the socket is a critical factor in the level of comfort the amputee experiences during gait. The ability to control local geometry is seen as an advantage of SLS in fabricating compliant sockets. This paper presents work on developing a model of compliance for sockets constructed of Duraform®. The approach taken here is to provide the necessary compliance by controlling the wall thickness of the socket. To select the right thickness, a study of the wall deflection with respect to contact pressure was performed. An experimental testing device was designed and constructed to test the deflection versus pressure for different thicknesses of test circular discs made of Duraform®. The results were correlated to a finite element model. These results will be used for designing the compliance in the walls of prosthetic sockets fitted to actual patients.
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    Clinical Evaluation of Prosthetic Sockets Manufactured by Selective Laser Sintering
    (2001) Rogers, Bill; Gitter, Andrew; Bosker, Gordon; Faustini, Mario; Lokhande, Mahendra; Crawford, Richard
    A pilot study was undertaken to evaluate the clinical acceptance of prosthetic limb sockets manufactured using solid freeform fabrication (SFF). The fabrication of sockets for amputees is a natural application for SFF. The socket is the part of the prosthetic limb that fits onto the amputee’s residual limb. Each socket is custom manufactured for each individual amputee. Four amputees were successfully fit with sockets created using selective laser sintering. The scope of the study included software development, finite element analysis, materials testing, and clinical evaluation. This paper discusses socket design issues and clinical testing results.
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    Automated Construction using Contour Crafting
    (2001) Khoshnevis, B.; Kwon, H.; Bukkapatnam, S.
    This paper presents some concepts and initial investigation of a novel construction automation approach using the Contour Crafting (CC) layered fabrication process, developed at the University of Southern California. CC uses computer control to take advantage of the superior surface forming capability of trowels, used by craftsmen and builders since ancient times, to create large intricate structures with smooth and accurate surfaces. The potential of CC became evident from the initial investigations and experiments with various materials and geometries. Using this process, a single house or a colony of houses, each with possibly a different design, may be automatically constructed in a single setup.
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    Simulation of the Electrochemical Machining Process
    (2001) Temur, R.; Coole, T.; Bocking, C.
    Electrochemical machining (ECM) or erosion, is a process for shaping materials by means of the anodic dissolution of a work-piece using suitably shaped cathodes? However, the predictability of the process is poor due to current density variations over the electrode contour leading to poor dimensional tolerances. This paper describes how the process can be entirely simulated by computer. A model of the electric field during erosion is constructed based on the Laplace equations for the field. From the distribution of the electric field, it is possible to continuously calculate the current density at each point on the work-piece for the whole machining process. In this way, it is possible to predict the final work-piece contour by running the simulation program instead of the real process. Simulations for cylindrical, conical and spherical electrodes were carried out and compared to actual eroded parts.
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    Software for the Interactive Configuration of RP Based Process Chains
    (2001) Dreher, Stefan
    In product development, time is one of the most critical factors. By introducing Rapid Prototyping methods, development time can be reduced dramatically. But the required characteristics of the generated prototypes become more and more complex. As a result, a great variety of Rapid Prototyping devices and services have emerged on the market. The product developer may be highly satisfied with the wide range of new potentials, tools and methods but who will give an orientation about the most suitable process chain to fulfill his demands? To solve the problem, a new software is being developed at the Fraunhofer Institute IPK in Berlin, the iViP-RPSelector. In a first step, the software tracks a record of the demands to the prototype. These values can be inserted manually, but there is an interface as well connecting the RPSelector to CAD and PDM systems to obtain the design parameters without user interaction. The RPSelector then calculates a completer RP based process chain, which may comprise a layer wise creation, some post processing, a copying process and several finishing processes.
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    Physical Modeling for Dynamic Control of Melting Process in Direct-SLS
    (2001) Ahn, S.; Murphy, J.; Ramos, J.; Beaman, J.J.
    During the melting process by laser irradiation, it is essential to understand the phase change processes to get high quality Direct SLS parts especially when highorder scanning paths are needed. This process is a transient three -dimensional heat conduction problem with a moving heat source and a moving phase boundary. The process can be simplified to a one-dimensional moving boundary model using appropriate assumptions. To implement a real-time control strategy, approximate solutions were found using three methods. Experiments using a CW CO2 laser were performed on low carbon steelsamples to verify the models’ results. By using first order differential equations derived from the model, multi-input multi-output (MIMO) control strategies can be applied.
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    Control of Laser Cladding for Rapid Prototyping--a Review
    (2001) Boddu, Mallikharjuna R.; Landers, Robert G.; Liou, Frank W.
    Lasers have wide–ranging applications in the manufacturing field (e.g., cladding, welding, cutting, machining, drilling). Extensive work is being conducted to apply laser cladding as a Rapid Prototyping (RP) process. In this paper the authors illustrate various principles of laser cladding in rapid prototyping. Important process parameters for the control of the laser cladding process are discussed as well as the experimental methods adopted, and results obtained by, various authors.
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    Empirical Modeling and Vision Based Control for Laser Aided Metal Deposition Process
    (2001) Boddu, Mallikharjuna; Musti, Srinivas; Landers, Robert G.; Agarwai, Sanjeev; Liou, Frank W.
    This paper gives a brief description of the laser aided manufacturing process. Empirical models describing the process dynamics of the laser aided metal deposition process is developed based on some of the models found in the literature. These models provide the basis for process planning and real time control. An embedded vision system, a two color temperature sensor, and a laser displacement sensor are incorporated for real time monitoring and control of the deposition process. The temperature profile of the surface and geometric characteristics of the melt pool are studied to ensure consistent operation of the process.