2004 International Solid Freeform Fabrication Symposium

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Proceedings for the 2004 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Fifteenth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 2-4, 2004, was attended by over 120 national and international researchers from sixteen countries. 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.

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 process development, design tools, modeling and control, process parameter optimization, applications 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.

This proceedings includes an edited transcript of a panel discussion held Tuesday afternoon at the meeting. Moderated by Harris Marcus of the University of Connecticut at Storrs, the panel topic was on the broader impacts of solid freeform fabrication. Panel members include David Alexander (Pratt and Whitney), Clinton Atwood (Sandia National Laboratory), Phill Dickens (Loughborough University, UK), and Kent Firestone (University of Texas at Austin).

This year’s best oral presentation was given by Jean-Pierre Kruth of the Katholieke Universiteit Leuven, Belgium. Selection is based on the overall quality of the paper, the presentation and discussion at the meeting, the significance of the work and the manuscript submitted to the proceedings. The paper title was, "Binding Mechanisms in Selective Laser Sintering and Selective Laser Melting". Selected from almost 70 oral presentations, his presentation appears on Page 44 of this Proceedings. The best poster presentation selected from 19 posters was given by Vito Gervasi of the Milwaukee School of Engineering. The paper title was, "Geometry and Procedure for Benchmarking SFF and Hybrid Fabrication Process Resolution" and appears on Page 493.

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 are grateful to Bryan Blackmur and Cindy Pflughoft who helped with Proceedings production. 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 (N00014-04-1- 0567) and the National Science Foundation (DMI 0412255) 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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    2004 International Solid Freeform Fabrication Symposium Table of Contents
    (2004) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Design and Fabrication of Components with Optimized Lattice Microstructures
    (2004) Gervasi, Vito R.; Stahl, Douglas C.
    The design and fabrication of components with optimized lattice microstructures is a new approach to creating lightweight high-performance objects. This paper introduces a unique and complete integration of design and fabrication leading to the creation of structural components with complex composite microstructures. Rather than a solid cast component with optimized outer shape this new approach leads to a component with an inner skeleton or microstructure maximizing one or more properties such as the stiffness-to-weight ratio. Three dimensional gradient materials are a natural outcome of this approach. An introduction to the design optimization and hybrid fabrication approach will be provided in addition to research progress and challenges through Spring 2004.
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    Multi-Nozzle Biopolymer Deposition for Freeform Fabrication of Tissue Constructs
    (2004) Khalil, S.; Nam, J.; Darling, A.; Sun, W.
    Advanced freeform fabrication techniques have been recently used for the construction of tissue scaffolds because of the process repeatability and capability of high accuracy in fabrication resolution at the macro and micro scales. Among many applicable tissue scaffolding materials, polymeric materials have unique properties in terms of the biocompatibility and degradation, and have thus been widely utilized in tissue engineering applications. Hydrogels, such as alginate, has been one of the most important polymer scaffolding materials because of its biocompatibility and internal structure similarity to that of the extracellular matrix of many tissues, and its relatively moderate processing. Three-dimensional deposition has been an entreating freeform fabrication method of biopolymer and particularly hydrogel scaffolds because of its readiness to deposit fluids at ambient temperatures. This paper presents a recent development of biopolymer deposition based freeform fabrication for 3-diemnsinal tissue scaffolds. The system configuration of multi-nozzles used in the deposition of sodium alginate solutions and Poly-?- Caprolactone (PCL) are described. Studies on polymer deposition feasibility and structural formability are conducted, and the preliminary results are presented.
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    Solid Freeform Fabrication of Artificial Human Teeth
    (2004) Wang, Jiwen; Shaw, Leon L.; Xu, Anping; Cameron, Thomas B.
    In this paper, we describe a solid freeform fabrication procedure for human dental restoration via porcelain slurry micro-extrusion. Based on submicron-sized dental porcelain powder obtained via ball milling process, a porcelain slurry formulation has been developed. The formulation developed allows the porcelain slurry to show a pseudoplastic behavior and moderate viscosity, which permits the slurry to re-shape to form a near rectangular cross section. A well-controlled cross-section geometry of the extrudate is important for micro-extrusion to obtain uniform 2-D planes and for the addition of the sequential layers to form a 3-D object. Human teeth are restored by this method directly from CAD digital models. After sintering, shrinkage of the artificial teeth is uniform in all directions. Microstructure of the sintered teeth is identical to that made via traditional dental restoration processes.
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    Laser Densification of Extruded Dental Porcelain Bodies in Multi-Material Laser Densification (MMLD) Process
    (2004) Li, Xiaoxuan; Wang, Jiwen; Shaw, Leon L.; Cameron, Thomas B.
    In this study commercial dental porcelain powder was deposited via slurry extrusion and laser densified to fabricate dental restorations in a Multi-Material Laser Densification (MMLD) process. The processing conditions for laser densification of single lines and closed rings were investigated in order to avoid warping and cracking. Multi-layer rings were also investigated to study the dependence of bonding between layers on the laser densification conditions. The laser densified rings showed no warping, and good bonding between layers could be achieved when the laser densification condition was selected properly. The mechanism to achieve porcelain rings without warping and cracking is discussed. The understanding developed will pave the way for fabricating a physical dental restoration unit.
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    Design and Manufacture of an Attachment Fitting for Transtibial Prosthetic Sockets Using Selective Laser Sintering
    (2004) Burhan, Danny; Crawford, Richard
    The focus of this work is using selective laser sintering to manufacture transtibial prosthetics sockets with compliant features to relieve contact pressure in sensitive areas. Each of these sockets requires an integrated attachment fitting to connect to the pylon and foot using standard hardware. Several design concepts of an attachment fitting are presented and compared. The design concepts were tested using a tensile test machine and analyzed using ground reaction force data to ensure a structurally sound connection. The resulting design employs standard hardware while maintaining the integrity of the connection for a normal gait cycle.
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    Fabrication of Bone Substitute Material by Rapid Prototyping
    (2004) Ott, A.; Heinzl, J.; Janitza, D.; Pelzer, R.
    Bone tissue engineering has gained much attention in recent years. A key requirement in this field is the development of scaffold structures, on which cells adhere. This can be done by fabricating scaffolds by direct procedures like 3D-printing or by indirect procedures like casting. With the 3D-printing process different structures were build up by using hydroxyapatite powder (HA) and a special binder material. Afterwards the printed 3D structures were sintered. For the casting process molds have been made of different resins by stereolithography and other processes using polymers and waxes. These structures were filled by a suspension of HA. By heating the resulting polymer/ceramic composite to a specific temperature it is possible to combust the polymer or wax. By further heating the remaining body, the HA is sintered. Compared to the 3D printing a better resolution can be obtained here. But there are restrictions regarding the ratio of polymer and the HA ceramic during the heating process which means a limitation for the level of porosity.
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    Orthopedic Surgery Planning Based on the Integration of Reverse Engineering and Rapid Prototyping
    (2004-08-30) Ahn, Dong-Gyu; Lee, Jun-Young; Yang, Dong-Yol
    This paper describes orthopedic surgical planning based on the integration of RE and RP. Using symmetrical characteristics of the human body, CAD data of the original bone without damages for the injured extent are generated from a mirror transformation of undamaged bone data for the uninjured extent. The physical model before the injury is manufactured from RP apparatus. Surgical planning, such as the selection of the proper implant, pre-forming of the implant, decision of fixation positions and incision sizes, etc., is determined by a physical simulation using the physical model. In order to examine the applicability and efficiency of surgical planning technology for orthopedics, various case studies, such as a proximal tibia plateau fracture, a distal tibia comminuted fracture and an iliac wing fracture of pelvis, are carried out. As a result of the examination, it has been shown that the orthopedic surgical planning based on the integration of RE and RP is an efficient surgical tool.
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    Accurate Heart Model for Pacemaker Development in SFF
    (2004) Crockett, R. S.; Horvath, T.; Koch, M.; Yang, M.
    Medical imaging combined with SFF techniques were used to create detailed CAD and physical heart models for commercial development of Pacemakers. Using a data set of 2D optical slice images of the human heart at 1mm spacing obtained from the Visible Human Project, a 3D CAD model was constructed by masking the features of interest in each slice. Normals on the resulting .stl file were inverted to create a single-piece mold, which was built in starch using 3D Printing. Flexible silicone was cast into this mold, and the starch was dissolved away to produce the final physical heart model. The resulting model simulates the mechanical properties of an actual heart, with medically accurate internal and external details including major veins & arteries, coronary sinus, etc.
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    Multiple Material Micro-Fabrication: Extending Stereolithography to Tissue Engineering and Other Novel Applications
    (2004-08-04) Wicker, Ryan; Medina, Francisco; Elkins, Chris
    A design for modifying an existing 3D Systems stereolithography (SL) apparatus 250/50 was developed to accommodate multiple material fabrication for building multi-material, multifunctional and multi-colored prototypes, models and devices. The machine was configured for automated access to an intermediate washing, curing, and drying unit that eliminated contamination between material vats and maintained accurate platform registration throughout the build process. Three vats were arranged on a rotating vat carousel, and each vat was adapted to actively maintain a uniform, desired level of material by including a recoating device and a material fill and removal system. A single platform was attached to an elevator mechanism (zstage) to traverse the platform to and from the vats and the washing, curing, and drying unit. The platform was mounted to the z-stage via an automated rotary stage to rotate the platform about a horizontal axis, thus providing angled building, washing, curing, and drying capabilities. A horizontal traversing mechanism was also designed to be optionally included to facilitate manufacturing between multiple SL cabinets, related SL apparatuses and/or other alternative manufacturing technologies. For micro-fabrication, linear and rotary stages were selected that provided ±1.0 µm repeatability and 0.1 µm resolution and ±2 arc sec repeatability and 0.13 arc sec resolution, respectively. The multi-material SL design presented here is capable of utilizing existing SL resins for manufacturing multiple material mechanically and electrically functional models as well as hydrogels, biocompatible materials, and bioactive agents for a variety of biofunctional, implantable tissue engineering applications including nerve regeneration and guided angiogenesis.
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    Biomimetic Design and Fabrication of Interior Architecture of Tissue Scaffolds Using Solid Freeform Fabrication
    (2004) Starly, B.; Lau, A.; Sun, W.; Lau, W.; Bradburyq, T.
    Modeling, design and fabrication of tissue scaffolds with intricate architecture, porosity and pore size for desired tissue properties presents a challenge in tissue engineering. This paper will present the details of our development in designing and fabrication of the interior architecture of scaffolds using a novel design approach. The Interior Architecture Design (IAD) approach seeks to generate scaffold layered freeform fabrication tool path without forming complicated 3D CAD scaffold models. This involves: applying the principle of layered manufacturing to determine the scaffold individual layered process planes and layered contour; defining the 2D characteristic patterns of the scaffold building blocks (unit cells) to form the Interior Scaffold Pattern; and the generation of process tool path for freeform fabrication of these scaffolds with the specified interior architecture. Feasibility studies applying the IAD algorithm to example models and the generation of fabrication planning instructions will be presented.
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    Soft and Hard Implant Fabrication Using 3D-Bioplotting TM
    (2004) Carvalho, C.; Landers, R.; Mülhaupt, R.
    At the Freiburger Materialforschungszentrum we have developed a new process (3DBioplotting TM) that permits most kind of polymers and biopolymers to be used in 3D scaffold design, including hydrogels (e.g. collagen, agar), polymer melts (e.g. PLLA, PGA, PCl) and twocomponent systems (e.g. chitosan, fibrin). Cells can be incorporated within the construction process, making this an ideal Rapid Prototyping technique for Organ Printing. Tailor-made biodegradable soft or hard scaffolds can so be fabricated in a short time using individual computer-tomography data from the patient. In-vitro tests showed promising results and in-vivo experiments are now under observation.
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    Direct Freeform Fabrication of Spatially Heterogeneous Living Cell-Impregnated Implants
    (2004-08-04) Cohen, D. L.; Malone, E.; Lipson, H.; Bonassar, L. J.
    The objectives of this work are the development of the processes, materials, and tooling to directly “3-D print” living, pre-seeded, patient-specific implants of spatially heterogeneous compositions. The research presented herein attempts to overcome some of the challenges to scaffolding, such as the difficulty of producing spatially heterogeneous implants that require varied seeding densities and/or cell-type distributions. In the proposed approach, living implants are fabricated by the layer-wise deposition of pre-cell-seeded alginate hydrogel. Although alginate hydrogels have been previously used to mold living implants, the properties of the alginate formulations used for molding were not suitable for 3-D printing. In addition to changing the formulation to make the alginate hydrogels “printable,” we developed a robotic hydrogel deposition system and supporting CAD software to deposit the gel in arbitrary geometries. We demonstrated this technology’s capabilities by printing alginate gel implants of multiple materials with various spatial heterogeneities, including, implants with completely embedded material clusters. The process was determined to be both viable (94±5% n=15) and sterile (less than one bacterium per 0.9 µL after 8 days of incubation). Additionally, we demonstrated the printing of a meniscus cartilage-shaped gel generated directly from a CT Scan. The proposed approach may hold advantages over other tissue printing efforts [5,9]. This technology has the potential to overcome challenges to scaffolding and could enable the efficient fabrication of spatially heterogeneous, patient-specific, living implants.
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    Industrial Freeform Generation of Microtools by Laser Micro Sintering
    (2004) Regenfuβ, P.; Hartwig, L.; Klötzer, S.; Ebert, R.; Brabant, Th.; Petsch, T.; Exner, H.
    Precision tools with structural resolution reaching the 20 micrometer range can be generated on an industrial scale by “laser micro sintering”. Components featuring aspect ratios above 12 and a roughness Ra down to 1.5 micrometers have already been produced from sub micrometer grained metal powders. The components can be generated either firmly attached to a substrate or fixed in an easily separable mode. If supporting structures are employed, undercuts up to 90° are feasible, without, a process parameter dependent maximum angles of undercut below 90° are obtained. The process has been introduced into the market, labeled microSINTERING by 3D-Micromac AG.
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    Freeform Fabrication of Electroactive Polymer Actuators and Electromechanical Devices
    (2004-09-01) Malone, Evan; Lipson, Hod
    In pursuit of the goal of producing complete electromechanical systems entirely via solid freeform fabrication, we are developing a library of mutually compatible, functional, freeform elements. Several essential elements – actuation, sensing, and control electronics - still remain to be incorporated into this library. Conducting polymers (CP) are a class of materials which can be used to produce all of these functionalities. Meanwhile, research into actuatable “smart” materials has produced other candidate materials for freeform fabricated actuators that are compatible with our library. We have succeeded in manually producing air-operable actuators that have processing and operating requirements that are compatible with our power source and mechanical component library elements. A survey of candidate actuator materials is presented, experiments performed with two types of actuator materials are described, and complete SFF-producible actuator devices are demonstrated.
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    Faster - Better Molds Through RSP Tooling New Research and Advancements
    (2004-08-19) Knirsch, James R.
    The recent developments in rapid production tooling have all but made the need for prototype tooling disappear. There are several approaches that are now as fast and inexpensive as prototype tooling, and after part approval can continue to run in high volume production applications. The newest of these approaches is an indirect spray forming process invented by Dr. Kevin McHugh of the Idaho National Engineering and Environmental Laboratories (INEEL). The advantages of RSP Tooling can be found in its accuracy, finish, cost and speed compared to the other rapid tooling processes [1]. The commercialization effort for this spray forming process started in February of 2002. The beta production machine was operational in November, 2003, and started to produce production tooling in March, 2004. Since that time tooling has been manufactured and run for many forming applications. In all but the simplest tools the process has proven to be less expensive and faster than standard machining of tools or any other rapid production tooling process. Research and development of the process has continued both at INEEL and at RSP Tooling, LLC making the process faster, more accurate and less expensive to operate. This research has also generated a better understanding of the underlying metallurgy of the process.
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    Ejection Forces and Friction Coefficients from Injection Molding Experiments Using Rapid Tooling Inserts
    (2004) Kinsella, M. E.; Lilly, B.; Carpenter, B.; Cooper, K.
    Experiments have been performed with injection mold inserts made using solid freeform fabrication processes in an effort to further study such applications for economic production of small quantities of parts. Static friction coefficients were determined for HDPE and HIPS against P-20 steel, sintered LaserForm ST-100, and stereolithography SL 5170 using the ASTM D 1894 standard. Injection mold inserts were constructed of the same three materials and were used to inject cylindrical parts using HDPE and HIPS. Ejection forces were measured, and a model was used to calculate ejection forces and apparent coefficients of static friction. Statistical analyses were used to determine the effects of packing time, cooling time and packing pressure on ejection force for the three insert types. This paper compares experimental and calculated ejection forces, compares standard friction test results to calculated apparent coefficients of friction, summarizes the statistical results, and comments on the feasibility of using rapid tooled inserts for injection molding.
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    Development of Nickel-Titanium Graded Composition Components
    (2004) Domack, M. S.; Baughman, J. M.
    The potential of various manufacturing methods was evaluated for producing nickel-titanium graded composition material. The selected test case examined attachment brackets that join nickel-based metallic thermal protection systems to titanium-based launch vehicle structure. The proposed application would replace nickel-based components with graded composition components in an effort to alleviate service induced thermal stresses. Demonstration samples were produced by laser direct metal deposition, flat wire welding, and ultrasonic consolidation. Microstructure, general bond quality, and chemistry were evaluated for the components.
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    Simulating the Effects of Substrate Pre-Heating on the Final Structure of Steel Parts Built by Laser Powder Deposition
    (2004) Costa, L.; Vilar, R.; Réti, T.
    Tool steel parts built by laser powder deposition often present a heterogeneous distribution of properties caused by the complex structural transformations that occur during the deposition process. A model describing these transformations has been developed. It couples finite element heat transfer calculations with transformation kinetic theory to predict the final microstructure and properties of the material and their variation across a laser powder deposited part. Pre-heating is often used to reduce the residual stresses and the risk of thermal distortion and cracking. However, this changes the heat transfer conditions and affects the final microstructure and properties. In this work the proposed model was used to evaluate the effects of substrate preheating on the final hardness distribution. The results show that the final hardness depends considerably on the initial temperature of the substrate.
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    Thermal Optimization of Injection Molds Produced by Layered Manufacturing Techniques
    (2004) Boillat, Eric; Glardon, Rémy; Matthey, Marc
    Producing injection tooling with cooling channels of almost any form seems to be one of the most promising advantages of Layered Manufacturing Techniques (like Selective Laser Sintering). It could be efficiently exploited to achieve higher productivity or better quality parts in injection molding. Unfortunately, at the present time, the lack of data-processing tools to design optimal cooling systems still prevents us from fully benefiting from this new potential. The first objective of this paper is to present a methodology for the optimal design of cooling systems in three-dimensional injection molds. Our optimization process is based on a finite element model of the mold and on the standard gradient method. In the second part of this paper, we compare a conventional mold and a mold equipped with a cooling system optimized by means of the proposed methodology. The comparison is carried out thanks to an appropriate protocol. The conclusion is that the optimization of the cooling system doubled the productivity of the mold.