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.