2010 International Solid Freeform Fabrication Symposium

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Proceedings for the 2010 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Twenty-First Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 9-11, 2010, was attended by almost 150 researchers from 11 countries. Papers addressed additive manufacturing issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. The diverse domestic and foreign attendees included industrial users, machine manufacturers, university researchers and representatives from the government.

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, modeling, applications and materials. We believe that documenting the changing state of the art in additive manufacturing through this Proceedings will serve both those presently involved in this fruitful technical area as well as new researchers and users entering the field.

A special session on government issues in additive manufacturing was held Monday morning. Participants discussed various aspects of additive manufacturing from the perspectives of users, funding agencies, standards producers and customers. Speakers were William Frazier (NAVAIR), Karen Taminger (NASA Langley), Mary Kinsella (AFRL) and Albert Wavering (NIST).

This year’s best oral presentation was given by Adriaan Spierings, Nikolaus Herres and Gideon Levy from inspire AG, St.Gallen, Switzerland and the Hochschule für Technik Buchs, Switzerland. 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, "Influence of the Particle Size Distribution on Surface Quality and Mechanical Properties in Additive Manufactured Stainless Steel Parts". Selected from 88 oral presentations, this presentation appears on Page 397 of this Proceedings. The best poster presentation selected from 22 posters was given by Shyam Barua, Todd Sparks and Frank Liou from the Missouri University of Science and Technology. The paper title was, "Development of a Low Cost Imaging System for a Laser Metal Deposition Process" and appears on Page 121.

This is the second year we have presented awards recognizing an outstanding junior and senior researcher in the field of additive manufacturing. The recipient of the International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Peter Mercelis, Managing Director of LayerWise, NV in Belgium. Dr. Gideon Levy, Research Manager and Head of the Institute for Rapid Product Development at iRPD-Inspire AG in St. Gallen, Switzerland, won the International Freeform and Additive Manufacturing Excellence (FAME) Award.

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 (N00014-10-1-0528) and the National Science Foundation (#CMMI-1028881) for supporting this meeting financially. The meeting was co-organized by the University of Connecticut at Storrs, and the Mechanical Engineering Department and the Laboratory for Freeform Fabrication at The University of Texas at Austin.


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    2010 International Solid Freeform Fabrication Symposium Table of Contents
    (2010) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Freeze Extrusion Fabrication of 13-93 Bioactive Glass Scaffolds for Bone Repair
    (University of Texas at Austin, 2010-09-23) Huang, T.S.; Doiphode, N.D.; Rahaman, M.N.; Leu, M.C.; Bal, B.S.; Day, D.E.
    There is an increasing demand for synthetic scaffolds with the requisite biocompatibility, internal architecture, and mechanical properties for the bone repair and regeneration. In this work, scaffolds of a silicate bioactive glass (13-93) were prepared by a freeze extrusion fabrication (FEF) method and evaluated in vitro for potential applications in bone repair and regeneration. The process parameters for FEF production of scaffolds with the requisite microstructural characteristics, as well as the mechanical and cell culture response of the scaffolds were evaluated. After binder burnout and sintering (60 min at 700°C), the scaffolds consisted of a dense glass network with interpenetrating pores (porosity ≈ 50%; pore width = 100−500 µm). These scaffolds had a compressive strength of 140 ± 70 MPa, which is comparable to the strength of human cortical bone and far higher than the strengths of bioactive glass and ceramic scaffolds prepared by more conventional methods. The scaffolds also supported the proliferation of osteogenic MLO-A5 cells, indicating their biocompatibility. Potential application of these scaffolds in the repair and regeneration of load-bearing bones, such as segmental defects in long bones, is discussed.
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    Towards Indirect Tissue Scaffold Fabrication via Additive Manufacturing and Hydroxyapatite Mineralization
    (University of Texas at Austin, 2010-09-23) Bernardo, Jesse; Samavedi, Satyavrata; Williams, Christopher B.; Morgan, Abby W.
    Unlike traditional stochastic scaffold fabrication techniques, additive manufacturing (AM) can be used to create tissue-specific three-dimensional scaffolds with controlled porosity and pore geometry. Directly fabricating scaffolds through AM methods is limited because of the relatively few biocompatible materials available for processing in AM machines. To alleviate these material limitations, an indirect fabrication method is proposed. Specifically, the authors investigate the use of Fused Deposition Modeling to fabricate scaffold patterns of varied pore size and geometry. The scaffold patterns are then mineralized with a biocompatible ceramic (hydroxyapatite). A heat treatment is then used to pyrolyze the pattern and to sinter the thin ceramic coating. The result is a biocompatible ceramic scaffold composed of hollow tubes, which may promote attachment of endothelial cells and vascularization [1]. In this paper, the authors explore the scaffold pattern fabrication and mineralization processes. Two scaffold pattern materials are tested [acrylonitrile butadiene styrene (ABS) and investment cast wax (ICW)] to determine which material is the most appropriate for scaffold mineralization and sintering. While the ICW could not be thoroughly mineralized despite a sodium hydroxide surface treatment, the ABS patterns were successfully mineralized following an oxygen plasma surface treatment. A 0.004 mm mineral coating was found on the ABS patterns that featured a strut offset of 0.3 mm, which is in the range of appropriate pore size for bone tissue engineering [2].
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    Bioresorbable Implants using Selective Laser Melting
    (University of Texas at Austin, 2010-09-23) Hoeges, S.; Lindner, M.; Meiners, W.; Smeets, R.
    Using bioresorbable materials implants can be manufactured which dissolve in the human body and are replaced by natural bone structure. For large implants an interconnecting porous structure needs to be integrated in the implant for a good vascularisation. Using additive manufacturing technology these internal structures can be directly manufactured. The structure can be designed by consequent following the guidelines of the medical expert. This paper describes the development of Selective Laser Melting to process bioresorbable materials Poly(D,L-lactide) and B-Tricalciumphosphate. The properties of the parts concerning microstructure, mechanical and biological properties after processing are analyzed in laboratory and animal tests. Possible applications are demonstrated and include individual bone substitute implants in cranio-maxillofacial surgery.
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    The Effects of Dry Heat Sterilization on Parts Using Selective Laser Sintering
    (University of Texas at Austin, 2010) George, Mitchell J.; Crawford, Richard H.
    Selective Laser Sintering (SLS) is a manufacturing process that can build arbitrarily shaped parts without part specific tooling. Its advantages have been employed in many different fields, one of these being medical surgery. Currently, SLS is limited in medical applications as a pre-operative modeling tool. For SLS manufacturing to progress in areas like compliant surgical tooling and patient specific bone matrices, concurrent work is needed to investigate the effects of medical sterilization on SLS materials. This paper presents the results of sterilization experiments on SLS parts built from nylon 11. To simulate the process of introducing tools into a sterile environment, these specimens were subjected to multiple rounds of dry heat sterilization. Changes to the dimensions, tensile strength and flexibility were recorded and analyzed. It was found that the specimens’ dimensions remained relatively constant. Both the tensile modulus and the flexural modulus decreased as the sterilization cycles progressed. The tensile modulus decreased by 25% and the flexure modulus decreased by 19% after ten rounds of sterilization.
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    Solid Freeform Fabrication Assisting Free Fibula Flap for the Reconstructive Surgery of Mandibular Defects
    (2010) Wang, Wanshan; Wu, Wenzheng; Yu, Tianbiao; Qin, Xingjun; Chen, Yadong; Rosen, David W.
    The usage of RP models can shorten the operation time for reconstructive surgery of mandible defects using the free fibula flap technique and can improve the accuracy of mandible reconstruction. This paper reports on a case study of reconstructive surgery on a patient with a mandibular defect caused by a tumor. A customized mandible rapid prototype model was manufactured from the patient’s CT data and was used to simulate the reconstructive surgery procedure. A customized titanium plate was shaped using the mandible RP model as a pattern before surgery. The usage of a mandible RP model reduced the operation time by 1.5-2.5 hours and the shape precision of the reconstructed mandible was improved. The customized titanium plate was consistent with the mandible anatomy.
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    Selective Laser Sintering and Freeze Extrusion Fabrication of Scaffolds for Bone Repair Using 13-93 Bioactive Glass: A Comparison
    (2010) Kolan, Krishna C.R.; Doiphode, Nikhil D.; Leu, Ming C.
    13-93 glass is a third-generation bioactive material which accelerates the bone’s natural ability to heal by itself through bonding with surrounding tissues. It is an important requirement for synthetic scaffolds to maintain their bioactivity and mechanical strength with a porous internal architecture comparable to that of a human bone. Additive manufacturing technologies provide a better control over design and fabrication of porous structures than conventional methods. In this paper, we discuss and compare some of the common aspects in the scaffold fabrication using two such processes, viz. selective laser sintering (SLS) and freeze extrusion fabrication (FEF). Scaffolds fabricated using each process were structurally characterized and microstructure analysis was performed to study process differences. Compressive strength higher than that of human trabecular bone was achieved using SLS process and strength almost comparable to that of human cortical bone was achieved using FEF process.
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    Design and Manufacturing of Bone Analog Models for the Mechanical Evaluation of Custom Medical Implants
    (2010-09-23) Horn, Timothy J.; Harrysson, Ola L.A.; Little, Jeffrey P.; West, Harvey A. Jr; Marcellin-Little, Denis J.
    The performance of orthopedic implants is often evaluated using cadaveric bone specimens. The high inter-specimen variability of cadaveric bone properties requires large sample sizes to obtain statistical significance. With recent focus on custom implants manufactured using direct metal freeform fabrication techniques, the need for a customized bone analog model is recognized. Data for bone geometry and internal structure were obtained from computed-tomography imaging. Traditional rapid prototyping techniques are then used to generate the rapid tooling from which composite bones that mimic the properties of the real bone can be duplicated. This work focused on the manufacturing process of bone analog models.
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    Patient-Specific Bone Implants using Subtractive Rapid Prototyping
    (2010) Frank, Matthew C.; Joshi, Ashish; Anderson, Donald D.; Thomas, Thaddeus P.; Rudert, M. James; Tochigi, Yuki; Marsh, J. Lawrence; Brown, Thomas D.
    This research involves the development of rapid manufacturing for patient-specific bone implants using a Subtractive Rapid Prototyping process. The geometry of segmental defects in bone, resulting from traumatic injury or cancerous tumor resection, can be reverse-engineered from medical images (such as CT scans), and then accurate defect fillers can be automatically generated in advanced synthetic or otherwise bioactive/biocompatible materials. This paper presents a general process planning methodology that begins with CT imaging and results in the automatic generation of process plans for a subtractive RP system. This work uniquely enables the rapid manufacturing of implant fillers with several key characteristics including; suitable bio-compatible materials and custom surface characteristics on specified patches of the filler geometry. This work utilizes a PLY input file, instead of the more common STL, since color texture information can be utilized for advanced process planning depending on whether the surface is fracture, periosteal or articular in origin. The future impact of this work is the ability to create accurate filler geometries that improve initial fixation strength and stability through accurate mating geometry, fixation planning and inter-surface roughness conditions. Keywords: Rapid Machining, Rapid Prototyping, Bone Implants, Surface Texturing
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    Interconnected Self-Propagating Photopolymer Waveguides: An Alternative to Stereolithography for Rapid Formation of Lattice-Based Open-Cellular Materials
    (2010) Jacobsen, A.J.; Kolodziejska, J.A.; Doty, R.; Fink, K.D.; Zhou, C.; Roper, C.S.; Carter, W.B.
    Recently, a new technique has been developed to create unique open-cellular materials with micro-scale truss, or lattice features ranging from tens to hundreds of microns. These materials are formed from a three-dimensional, interconnected array of self-propagating photopolymer waveguides. By utilizing this self-propagating effect, three-dimensional open-cellular polymer materials can be formed in seconds. In addition, intrinsic to the process is the ability to control specific micro-lattice parameters which ultimately affect the bulk material properties. Unlike stereolithography, this new fabrication technique is rapid (~ minutes to form an entire part) and relies on a single two-dimensional exposure surface to form three-dimensional structures (thickness > 25 mm possible). This combination of speed and planar scalability opens the possibility for large-scale mass manufacturing. The utility of these new materials range from lightweight energy absorbing structures to thermal management materials to bio-scaffolds.
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    Design and Additive Fabrication of Foot and Ankle-Foot Orthoses
    (University of Texas at Austin, 2010) Pallari, J.H.P.; Dalgarno, K.W.; Munguia, J.; Muraru, L.; Peeraer, L.; Telfer, S.; Woodburn, J.
    Foot and ankle-foot orthoses are prescribed in order to promote mobility through supporting and/or realigning the lower leg and alleviating pain in the foot in different parts of the gait cycle. This paper will outline new approaches to the design and manufacture of personalised foot and ankle-foot orthoses (FO and AFO) using additive fabrication technology. The research is addressing the need for specific software design tools for orthosis design which enable their properties to be locally tailored within a mass customisation framework. Structure/material testing to support that activity is also being undertaken and will be described.
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    SLS Nylon 12 Characterization Through Tensile Testing and Digital Image Correlation for Finite Element Modeling of Food and Ankle-Foot Orthoses
    (University of Texas at Austin, 2010) Muraru, L.; Pallari, J.; Creylman, V.; Vander Sloten, J.; Peeraer, L.
    Selective Laser Sintering has been recently proposed as a feasible engineering technique for manufacturing of customized ankle-foot orthoses (AFOs). Development of computer-aided design (CAD) models and virtual evaluation of the orthotic devices are important steps in the engineering design process. This paper will describe a method for accurate characterization of SLS Nylon 12 mechanical properties to be implemented in the finite element models (FEM) of AFOs. Elastic mechanical properties were determined for principal and perpendicular building directions.
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    Custom, Integrated, Pneumatic, Rotary Actuator for an Active Ankle-Foot Orthosis
    (University of Texas at Austin, 2010) Remmers, Richard; Cook, Doug; Gervasi, Vito
    End-use objects produced via additive manufacturing (AM) are on the rise and new applications in the fluid power industry are emerging. Recently, a custom, pneumatic, rotary actuator was been designed and additively manufactured for integration into an active ankle-foot orthosis that is being developed in the National Science Foundation’s Center for Compact and Efficient Fluid Power. All necessary plumbing, between the valves and vanes, is integrated into the additively-manufactured housing of the actuator; and, the silicone translating seals were vacuum-transfer molded using additively-manufactured molds and inserts. This nonconventional actuator has more theoretical torque, and weighs less, than the off-the-shelf component that it replaced. Further development will reduce seal leakage, and optimize designs for additional mass reduction. Results-to-date are presented, in addition to several other examples of the growing use of AM in the fluid-power industry.
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    Multi-Material Food Printing with Complex Internal Structure Suitable for Conventional Post-Processing
    (University of Texas at Austin, 2010-09-23) Lipton, Jeffrey; Arnold, Dave; Nigl, Franz; Lopez, Nastassia; Cohen, Dan; Norén, Nils; Lipson, Hod
    Solid Freeform Fabrication (SFF) of food provides an exciting application for additive manufacturing technologies. A variety of materials has been used to demonstrate food printing. However, these materials were not suited for traditional food processing techniques (Baking, slow cooking, frying, etc) and thus eliminating the majority of today‟s consumed food. We demonstrated new materials suitable for baking, broiling and frying. Turkey, scallop, celery were processed and modified using transglutaminase to enable them to be slow cooked or deep-fried after printing. Mutli-material constructs of turkey meat and celery were successfully printed. A cookie recipe was modified to be printable while retaining shape during baking. By adding cocoa powder to the modified recipe a second, visually and differently tasting material was created. A complex shape of the cocoa modified material was printed within a block of the modified material. The complex internal geometry printed was fully preserved during baking.
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    Development of Technique for 3D Printed Mould Intricate Rapid Casting
    (University of Texas at Austin, 2010-09-23) Brabazon, Dermot; Kennedy, Donal; Tyrell, Michael
    The development of rapid prototyping (RP) technologies has proven highly significant in the efforts to reduce production times for a number of casting processes. Although rapid prototyping technologies have most commonly be used to produce patterns for investment and sand casting this study demonstrated the use of direct shell production casting using three dimensional printing technology. Statistical methods as well as thermal, visual and dimensional analysis were also applied in order to optimise this rapid casting (RC) process for thin wall non-ferrous parts. Mould dimensions within ± 0.22 mm were achieved with the developed technique. Higher melt temperatures and pouring pressures produced castings with better dimensional accuracy. Mould temperature was not found to affect the casting dimensional accuracy significantly. The results allow for better dimensional specification of CAD file geometry for the rapid casting process.
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    Laser Based Rapid Manufacturing of Metallic Gas Diffusion Layers for PEM Fuel Cells
    (University of Texas at Austin, 2010-09-23) Tandra, Gargi; Sparks, Todd Eugene; Barua, Shyam; Kulkarni, Nikhil P.; Liou, Frank
    Gas Diffusion layers (GDL’s) are an essential component of Polymer Electrolyte Membrane Fuel cells (PEMFC’s) which aid in thermal & electrical conductivities, water management and act as backup layers for the membrane electrode assemblies. This paper summarizes the effort to prototype metallic GDL designs using a miniature laser deposition system developed at Missouri University of Science & Technology. The pore sizes are controlled by masking the diverging laser beam using stainless steel masks of varying sizes and shapes. The through pore feature and further treatment of the GDL’s for hydrophobicity reduces the water management issue and thereby increases the performance of the fuel cells. The operational characteristics of the GDL can be optimized by understanding the effect of the key parameters like fluid permeability, porosity, hydrophobicity and the surface morphology.
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    MEA Manufacturing Using an Additive Manufacturing Process to Deposit a Catalyst Patter in an MEA and its Impact on Cost Reduction
    (University of Texas at Austin, 2010) Kulkarni, N.P.; Sparks, T.E.; Tandra, G.; Liou, F.W.
    The manufacturing of a fuel cell Membrane Electrode Assembly (MEA) is a significant cost driver in polymer-electrolyte membrane (PEM) fuel cell technologies, primarily due to the inclusion of expensive materials in the catalyst layer. The selective deposition of a catalyst on the MEA of a fuel cell can drastically reduce the costs depending upon the catalyst, method used for deposition, and production volume. In this paper, testing and analysis of a novel catalyst iridium oxide is discussed. The performance of the catalyst will be compared with the conventional catalysts which will give us an estimate of its effectiveness however, in this paper, only its feasibility in terms of cost is discussed.
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    Fabrication and Testing of Graphite Bipolar Plates for Direct Methanol Fuel Cells
    (University of Texas at Austin, 2010-09-23) Alayavalli, Kaushik; Bourell, David L.
    Bipolar plates made from graphite are highly desirable in fuel cell applications due to the properties of high electrical conductivity, low weight and resistance to corrosion that graphite possesses. However, the poor mechanical properties of natural graphite lead to prohibitive machining costs. Graphite parts are made by indirect SLS using graphite powder mixed with a phenolic resin binder which is subsequently burnt out. These parts fabricated using indirect SLS have poor green strength and electrical conductivity. The current work deals with the addition of carbon fiber to the graphite-phenolic mixture with an aim to improve green part strength and brown part conductivity. This research work also addresses fabrication of graphite bipolar plates for Direct Methanol Fuel Cells (DMFCs) with internal features and flow channels with different cross-sectional geometry that are difficult to produce using conventional machining processes.
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    Freeform Fabrication of Stochastic and Ordered Cellular Structures
    (University of Texas at Austin, 2010) Lipton, Jeffrey; Boban, Mathew; Hiller, Jonathan; Lipson, Hod
    Cellular materials provide a unique challenge to SFF technology. Such materials have unique properties of low mass, high strength, and good insulation properties. To produce such cellular structures, SFF systems require a designed microstructure with a feature size significantly lower than the resolution of the process. In this paper, we examine means of producing stochastic foams using the instability of a viscous thread and various methods for production of closed celled foams. These techniques allow for the production of foams without the need for pre-described cell structures. Such foams, when made from elastic materials can act as novel actuating materials.
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    Self Assembly as an Additive Manufacturing Process: Opportunities and Obstacles
    (University of Texas at Austin, 2010-09-23) Crane, N.B.; Tuckerman, J.; Nielson, G.N.
    While additive manufacturing processes typically integrate functionally identical building blocks, biological growth depends on the precise assembly of molecular building blocks to achieve the remarkable functionality observed in living systems. This paper considers potential performance benefits and challenges of producing systems by controlled assembly of functional components. The work will consider the impact of self-assembly errors in two energy applications: miniature thermoelectric devices and microscale photovoltaic cells. In both, high performance is possible by assembling microscale components. While assembly errors can reduce system performance, performance models show that high levels of system performance can be achieved through system design and/or self-assembly process control.