2011 International Solid Freeform Fabrication Symposium

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Proceedings for the 2011 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Twenty-Second Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 8-10, 2011, was attended by almost 160 researchers from 11 countries. The weather this year was notable, and participants got to experience history in the making. August was the hottest month recorded in Austin in over 100 years in the hottest summer of the hottest year. The average daily high temperature for the month was 104.8 F (40.4 C). There were only 2 days in August under 100 F (37.8 C), and an Austin daily record was set during the meeting on Aug. 9 (106 F, 41.1 C). Austin had 90 days in 2011 over 100 F which shattered the old record of 69 days.

A special session on “Sustainability in Additive Manufacturing” was held Tuesday morning. The topics reflected the broad issues of the topic, including energy and resource efficiency, waste stream generation, thermal issues, recycling and process effects.

This year’s best oral presentation was given by Kamran Mumtaz, Pratik Vora and Neil Hopkinson from Loughborough University in the United Kingdom. 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, "A Method to Eliminate Anchors/Supports from Directly Laser Melted Metal Powder Bed Processes". Selected from 76 oral presentations, this presentation appears on Page 55 of this Proceedings. The best poster presentation selected from 18 posters was given by David Brackett, Ian Ashcroft and Richard Hague, also from Loughborough University. The paper title was, "Topology Optimization for Additive Manufacturing", and the paper appears on Page 348.

The recipient of the International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Candice Majewski, a member of the Additive Manufacturing Research Group at Loughborough University, in the United Kingdom. Dr. David Bourell, Temple Foundation Professor and Director of the Lab for Freeform Fabrication at The University of Texas at Austin, 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, as well as her excellent performance as registrar and problem solver during the meeting. Brandon Fusco is largely responsible for creation of the conference proceedings, for which we are grateful. We would like to thank the Organizing Committee, the session chairs, the attendees for their enthusiastic participation, 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 additive manufacturing 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- 1131662) 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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    2011 International Solid Freeform Fabrication Symposium Table of Contents
    (2011) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Additive Manufacturing (AM) and Nanotechnology: Promises and Challenges
    (University of Texas at Austin, 2011-08-17) Ivanova, Olga S.; Williams, Christopher B.; Campbell, Thomas A.
    The narrow choice of materials used in Additive Manufacturing (AM) remains a key limitation to more advanced systems. Nanomaterials offer the potential to advance AM materials through modification of their fundamental material properties. In this paper, the authors provide a review of available published literature in which nanostructures are incorporated into AM printing media as an attempt to improve the properties of the final printed part. Specifically, we review the research in which metal, ceramic, and carbon nanomaterials have been incorporated into AM technologies such as stereolithography, laser sintering, fused filament fabrication, and three-dimensional printing. The purpose of this article is to summarize the research done to date, to highlight successes in the field, and to identify opportunities that the union of AM and nanotechnology could bring to science and technology.
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    Robust Design of Negative Stiffness Elements Fabricated by Selective Laser Sintering
    (University of Texas at Austin, 2011) Shahan, David; Fulcher, Ben; Seepersad, Carolyn Conner
    Constrained negative stiffness structures have been shown to possess desirable vibration isolation properties because of their ability to provide low dynamic stiffness, resulting in low transmissibility over a wide range of frequencies. In this research, selective laser sintering (SLS) is an integral part of a model-design-build-test process for investigating the vibration isolation capabilities of negative stiffness structures in the form of axially compressed beams. SLS provides geometric design freedom and rapid fabrication capabilities for validating dynamic models of structural behavior and guiding the design process toward iterative improvements. SLS also introduces some geometric and dimensional variability that can significantly degrade the performance of the structure. In this paper, an iterative model-design-build-test process for negative stiffness structures is described and presented with an analysis of the impact of SLS-induced imperfections on the results.
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    Effective Thermal Conductivities of Unit-Lattice Structures for Multi-Functional Components
    (University of Texas at Austin, 2011) Cook, D.; Newbauer, S.; Pettis, D.; Knier, B.; Kumpaty, S.
    Approaching the goal of automatically generating optimized multi-functional components, previously-identified unit-lattice structures are being characterized for their geometry-dependent, effective, thermal conductivities. This knowledge base will allow for the definition of low-mass, load-bearing, thermal-management structures. One application is a wearable power source for a custom, portable, active orthosis. The function of this structure is to bear mechanical load while dissipating heat from the source, without burning the wearer. Additive manufacturing affords the capability of fabricating the resultant complex structures. Current research efforts are using finite-element analysis and physical testing to validate the characteristic models, and determining the scale dependence of internal-convective-flow development. Future work will include composites.
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    Selective Laser Melting of Porous Structures
    (University of Texas at Austin, 2011-08-17) Stoffregen, H.A.; Fischer, J.; Siedelhofer, C.; Abele, E.
    Within the Center of Smart Interfaces “Understanding and Designing Fluid Boundaries”, a German Excellence Initiative, the Institute of Production Management, Technology and Machine Tools examines the manufacturing of porous structures by using selective laser melting (SLM). In this paper two different strategies are presented in order to obtain porosity: One strategy is to manufacture geometrically defined lattice structures. SLM allows here complex geometries that cannot be manufactured by conventional technologies to be built. The second approach is to manufacture geometrically undefined porosity by a specific modification of exposure parameters. The SLM generated porous structures are investigated with respect to the heat and mass transfer. The research focus is to increase the efficiency of spraycooling effects and the manipulation of the Leidenfrost point.
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    A Dithering Based Method to Generate Variable Volume Lattice Cells for Additive Manufacturing
    (University of Texas at Austin, 2011-08-17) Brackett, D.; Ashcroft, I.; Hague, R.
    This paper covers the principles of a novel method to efficiently spatially vary the size of tetrahedral cells of a lattice structure, based upon finite element analysis stress results. A dithering method, specifically error diffusion, is used to represent a grayscale stress fringe with variably spaced black dots. This enables linkage of the spacing between lattice cell vertices to stress level thereby providing a functional variation in cell density. This method is demonstrated with a simple test case in 2D and the steps involved for extension to 3D are described.
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    Optimal Design of a Golf Club using Functionally Graded Porosity
    (University of Texas at Austin, 2011-08-17) Ray, Phillip; Chahine, Gilbert; Smith, Pauline; Kovacevic, R.
    The current work portrays a new concept of designing and manufacturing golf club heads with functionally graded porosity (FGP) by means of electron beam melting® (EBM®). In light of the advancement of additive manufacturing (AM) technologies and the consequent wide spread applications in the aerospace, automotive, and biomedical industries, the current work discusses a new application in sport technologies; for example, in the golf industry. EBM® makes it possible to print the designed porosity within a golf club head, to reduce the weight and optimize performance. The focus is to design the golf club head with FGP to improve performance and reduce weight. The dynamic properties of porous materials are investigated theoretically. The porosity in the club head was analyzed numerically by simulating the impact between the club head and a steel ball in order to determine the coefficient of restitution (COR) of the club head. The simulation’s parameters are in compliance with the U.S Golf Association’s (USGA) test procedure for measuring COR.
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    Printed Circuit Boards By Selective Deposition and Processing
    (University of Texas at Austin, 2011-08-17) Jones, J.B.; Wimpenny, D.I.; Chudasama, R.; Gibbons, G.J.
    With electronic applications on the horizon for AM, comes the dilemma of how to consolidate conductors, semi-conductors, and insulators in close proximity. To answer this challenge, laser printing (selective deposition) was used in tandem with fiber laser consolidation (selective processing) to produce PCBs for the first time. This combination offers the potential to generate tracks with high mechanical integrity and excellent electrical conductivity (close to bulk metal) without prolonged exposure of the substrate to elevated temperatures. Herein are the findings of a two-year feasibility study for a “one-stop” solution for producing PCBs (including conductive tracks, dielectric layers, protective resists, and legends).
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    Indirect Laser Sintering of Corrugated Flow Field Plates for Direct Methanol Fuel Cell Applications
    (University of Texas at Austin, 2011-08-17) Chakravarthy, Kumaran M.; Bourell, David L.
    Direct methanol fuel cells (DMFC) hold distinct advantages over traditional hydrogen-based fuel cells. Their commercialization, however, has been bound by many factors – especially their suboptimal efficiency. This work aims at enhancing the performance of DMFC through the use of corrugated flow field plates. Our objectives are two-fold – one, to increase the power density of DMFC by corrugating flow field plates and two, to introduce Laser sintering (LS) as an efficient and robust method for the manufacture of such plates. Corrugated flow field plates with 10% more surface area as compared to a planar design were made by LS & tested in a DMFC environment. Our results show that the particle size of the material used – Graphite – has a significant effect upon the green strength of LS parts. We also report the performance of corrugated flow field plates with 10% higher surface area (as compared to planar plates), channel width and depth of 2mm and an electrode area of 5 cm2. This study is the first experimental approach to the use of indirect LS for making such fuel cell components.
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    Bio-Inspired Design of Bipolar Plate Flow Fields for Polymer Electrolyte Membrane Fuel Cells
    (University of Texas at Austin, 2011-08-17) Guo, Nannan; Leu, Ming C.; Wu, Maoliang
    The flow field of a bipolar plate distributes hydrogen and oxygen for polymer electrolyte membrane (PEM) fuel cells and removes the produced water from the fuel cells. It greatly influences the performance of fuel cells, especially regarding reduction of mass transport loss. Flow fields with good gas distribution and water removal capabilities reduce the mass transport loss, thus allowing higher power density. Inspired by natural structures such as veins in tree leaves and blood vessels in lungs, which efficiently feed nutrition from one central source to large areas and are capable of removing undesirable by-products, a mathematic model has been developed to optimize the flow field with minimal pressure drop, lowest energy dissipation, and uniform gas distribution. The model can be used to perform optimal flow field designs, leading to better fuel cell performance for different sizes and shapes of bipolar plates. Finite element modeling (FEM) based simulations and in-situ experiments were conducted to verify some of the flow field designs obtained using the developed mathematic model.
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    Combined SFF Patterning and Replica Molding for Microfabrication of Cell-Laden Microfluidic Device
    (University of Texas at Austin, 2011) Snyder, Jessica; Wang, Chengyang; Hamid, Qudus; Sun, Wei
    We report on a novel technique using additive manufacturing to fabricate a cell-laden polydimethylsiloxane (PDMS) microfluidic device by SFF processes and replica molding. We demonstrate concept feasibility and present results using single and multiple layer patterns. 3-dimensional channel architecture is achieved by CAD/CAM technology and tuning manufacturing process parameters. Our microfluidic device is fabricated in two stages (1) print negative mold by thermal extrusion of polycaprolactone (PCL) using layer-by-layer precision extrusion deposition then (2) casting PDMS. Cells and matrix are selectively assembled inside microchannels using multi-nozzle printing to demonstrate feasibility of chip as a culture environment. The objective of this work is to fabricate a cell-laden microfluidic device by combined solid freeform patterning and replica molding with direct cell writing into channels. This work has application as a 3D physiological model for in vitro pharmacokinetic study in space environment in preparation for long term manned missions.
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    A Method for Creating Actuated Joints via Fiber Embedding in a Polyjet 3D Printing Process
    (University of Texas at Austin, 2011-08-17) Stiltner, L. Justin; Elliott, Amelia M.; Williams, Christopher B.
    The Objet PolyJet direct 3D Printing process is capable of simultaneously depositing two distinct photopolymer materials in preset combinations to enable designers to create parts with graded material properties. For example, this dual-jet process offers designers the ability to combine elastomeric and rigid materials in order to create integrated assemblies featuring stiff components and flexible joints and gaskets. To expand the potential of this technology, the authors have developed a method for the direct fabrication of systems with actuated joints without post-process assembly. The method, which involves temporarily pausing the build process and embedding and anchoring fibers into the part, is described in this paper along with part design considerations. Two systems featuring actuated joints are presented as a means of displaying the embedding method’s capabilities.
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    Indirect Tissue Scaffold Fabrication via Fused Deposition Modeling and Biomimetic Mineralization
    (University of Texas at Austin, 2011-08-17) Bernardo, Jesse; Samavedi, Satyavrata; Williams, Christopher B.; Whittington, Abby R.
    To alleviate material limitations of the additive manufacture of tissue scaffolds, researchers have looked to indirect fabrication approaches. The feature resolution of these processes is limited however, due to the viscous ceramic slurries that are typically employed. To alleviate these limitations, the authors look to an indirect fabrication process wherein a pattern, created using Fused Deposition Modeling, is biomimetically mineralized with an aqueous simulated body fluid, which forms a bonelike hydroxyapatite throughout the scaffold pattern. Mineralized patters are then heat treated to pyrolyze the pattern and sinter the minerals. With this process, scaffolds were created with wall thicknesses as small as 150 m and internal channel diameters of 280-340 m, an appropriate range for bone tissue engineering.
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    Manufacturing of Complex Parts with Continuous Functionally Graded Materials (FGM)
    (University of Texas at Austin, 2011-08-17) Hascoet, J.Y.; Muller, P.; Mognol, P.
    One of major evolutions of the additive manufacturing is the ability to produce parts with functionally graded materials (FGM). However, manufacturing of these parts is limited to discrete or nearly continuous FGM on samples. To achieve this, it is necessary to have a global control of processes and to develop methodologies to help designers and manufacturers. A methodology to produce morphologically complex parts is proposed in this paper. It consists in classifying all typologies of bi-materials gradients with mathematical description. Each typology of gradient is associating with manufacturing strategies in order to choose slicing and path strategies. Afterwards, mathematical data are used to have a global control of a process. This paper presents the principle of this methodology and the mathematical models which are chosen to describe part and manufacturing.
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    Comparison off Selective Laser and Electron Beam Melted Titanium Aluminides
    (University of Texas at Austin, 2011) Loeber, L.; Biamino, S.; Ackelid, U.; Sabbadini, S.; Epicoco, P.; Fino, P.; Eckert, J.
    In the following paper we present the investigation of microstructure and mechanical properties produced by selective laser melting (SLM) and electron beam melting (EBM). The chosen alloy is a Ti-(46- 48)Al-2Cr-2Nb alloy which has a great potential in replacing heavy weight Ni-base superalloys in turbine blades. Cylindrical specimens were produced and characterized by optical microscopy (OM), scanning electron microscopy (SEM) and chemical analysis to determine the microstructure and composition. In addition compression tests at room and elevated temperatures (700-800 °C) were carried out to identify the mechanical properties of the alloy.
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    SLM of Net-Shaped High Strength Ceramics: New Opportunities for Producing Dental Restorations
    (University of Texas at Austin, 2011-08-17) Hagedorn, Y.-C.; Balachandran, N.; Meiners, W.; Wissenbach, K.; Poprawe, R.
    Oxide ceramics yield excellent mechanical properties along with outstanding thermal and wear resistance. However, little work on additive Manufacturing (AM) of high-strength ceramics has been stated. In the present paper the current state of development in Selective Laser Melting (SLM) of pure ceramic specimens is reviewed. During the present approach the eutectic mixture of pure alumina (Ah0 3) and zirconia (Zr02) powder is completely molten while crack formation is prevented by a high-temperature C02-Iaser preheating. This approach yields net-shaped, fully dense specimens reaching flexural strengths of above 500 MPa without post-processing. One potential application for this technology are fully-ceramic dental restorations frameworks, as the demanded maximum loads of above I 000 N are met. Alternative preheating strategies are presented to allow for manufacturing larger volumetric parts.
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    Effect on Particle Size, Binder Content and Heat Treatment on Mechanical Properties of 13-93 Bioactive Glass Scaffolds
    (University of Texas at Austin, 2011-08-17) Kolan, Krishna C.R.; Leu, Ming C.; Hilmas, Gregory E.; Velez, Mariano
    Particle size, binder content and the post-processing schedule are important parameters that affect the microstructure, and, hence, the mechanical properties of parts produced using the indirect selective laser sintering process. 13-93 bioactive glass, with mean particle sizes ranging from 10 µm to 44 µm, is mixed with different amounts of stearic acid binder to fabricate green scaffolds. Through the design of the post-processing schedule, the time required for postprocessing the green scaffolds is reduced from the initial 80 hrs to 12 hrs. The compressive strength varies from 41 MPa for a part with ~60% porosity to 157 MPa for a part with no designed porosity. Several batches of 13-93 scaffolds are soaked in a simulated body fluid for different time intervals ranging from 1 week to 6 weeks. The amount of hydroxyapatite formed and subsequent mechanical properties are provided and discussed.
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    Gas Phase Solid Freeform for Fabrication of Three-dimensional Ceramic Structures
    (University of Texas at Austin, 2011) Weiss, Clayton; Marcus, Harris L.
    Solid free form of ceramic materials can be achieved by deposition from the gas phase. The Selective Area Laser Deposition, or SALD, technique can be utilized to make ceramic depositions with a uniform chemical composition. In order to make all classes of ceramics, including carbides, nitrides, and oxides, selection of a precursor is an essential step. Often the correct precursor for the deposition requires a special environment, namely, one that can be uniformly heated. System design for a heated deposition chamber is discussed as well as preliminary tests of the system functionality. Silicon Carbide depositions were performed as a means of evaluating system parameters.
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    Combined Effects of Montmorillonite Clay, Carbon Nanofiber, and Fire Retardant on Mechanical and Flammability Properties of Polyamide 11 Nanocomposites
    (University of Texas at Austin, 2011) Johnson, Blake; Allcorn, Eric; Baek, Min G.; Koo, Joseph H.
    This paper is focused on the development of polyamide 11 (PA11) nanocomposites with enhanced fire retardant (FR) properties for application in selective laser sintering (SLS). Test specimens of PA11 containing various percentages of intumescent FR additive, montmorillonite (MMT) clay, and carbon nanofiber (CNF) were prepared via the twin screw extrusion technique. The combined effects of MMT clay, CNF, FR additives on the mechanical and flammability properties of these PA11 nanocomposites are studied. Izod impact testing, tensile testing, and SEM analysis of are used to characterize mechanical properties. UL-94 and SEM analysis of char surfaces are used to characterize the flammability properties of these materials. Results are analyzed to determine any synergistic effects among the additives to the material properties of PA11.
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    Experimental and Theoretical Analysis of Scanning Laser Epitaxy Applied to Nickel-Based Superalloys
    (University of Texas at Austin, 2011) Bansal, R.; Acharya, R.; Gambone, J.J.; Das, S.
    This paper reports on the experimental development and the theoretical analysis of the scanning laser epitaxy (SLE) process that is currently being investigated and developed at the Georgia Institute of Technology. SLE is a laser-based manufacturing process for deposition of equiaxed, directionally solidified and single-crystal nickel superalloys onto superalloy substrates through the selective melting and re-solidification of superalloy powders. The thermal modeling of the system, done in a commercial CFD software package, simulates a heat source moving over a powder bed and considers the approximate change in the property values for consolidating CMSX-4 nickel superalloy powder. The theoretical melt depth is obtained from the melting temperature criteria and the resulting plots are presented alongside matching experimental micrographs obtained through cross-sectional metallography. The influence of the processing parameters on the microstructural evolution, as evidenced through observations made from the micrographs, is discussed.