1990 International Solid Freeform Fabrication Symposium

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Proceedings for the 1990 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.


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    1990 International Solid Freeform Fabrication Symposium Table of Contents
    (1990) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Thermal Properties of Powders
    (1990) Xue, Samuel; Barlow, J.W.
    This paper presents measurements of the specific heats of various powders, including nylon, ABS, PVC, and two kinds of wax. An unsteady-state conduction technique is also presented for measuring the thermal conductivities of these powders at temperatures below those where sintering occurs. Both specific heats and thermal conductivities are found to be functions of temperature.
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    Solid Modeling and Stereolithography as a Solid Freeform Fabrication Technique at Texas Instruments Incorporated
    (1990) Baumgardner, Owen; Blake, Paul
    Over the past 25 years, the CAE/CAD/CAM industry has developed technological advances that have provided industrial users the ability to increase productivity and decrease the cycle time necessary for product development. These technologies include basic wireframe and surface design, specializedapplication software packages, finite element analysis, numerical control, solid modeling, and rapid prototyping. Each of these technologies plays a significant role in industry today. The Defense Systems & Electronics Group of Texas Instruments currently uses these technologies in the mechanical design engineering process. This paper discusses the two specific technologies of solid modeling and rapid prototyping (specifically stereolithography), including their advantages, benefits, and practical applications within the Texas Instruments Defense Systems & Electronics Group. This paper also discusses the use of stereolithography (SLA) rapid~prototype parts within the solid-mold investment~casting process.
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    Sintering Rates in the Selective Laser Sintering Process
    (1990) Nelson, Christian; Barlow, J.W.
    This paper presents. a procedure to determine rates of sintering as a function of temperature using an isothermaloven. The rate of height change of a powder sample in the oven at temperatures near the Tg or Tm is measured. From this information an activation energy is calculated. This activation energy is similar to activation energies calculated from viscosity versus ternp.erature curves for polymer melts. This similarity suggests that viscous sint~ring models such. as those by Frenkel and Scherer are appropriate. A comparison between sintering rates of polymer coated alumina powder and mixed powders of the polymer with alumina, suggest that better sintered products may result from the coated powders than from simple mixtures.
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    A Computer Model for Laser Photopolymerization
    (1990) Flach, Lawrance; Chartoff, Richard P.
    A computer model for a laser induced photopolymerization process has been established which simulates stereolithography. The model couples irradiation, chemical reaction, and heat transfer equations to provide insights into rate processes occurring in the volume element contacted by the laser beam. Quantities predicted include the spatial variation in conversion of monomer to polymer, depletion of photoinitiator, and local variations in temperature in and around the spot contacted by the laser. This allows predictions to be made about the laser dwell time, depth penetration and uniformity of the photopolymer formed in the process.
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    Parametric Analysis of the Selective Laser Sintering Process
    (1990) Martin Sun, Ming-shen; Beaman, Joseph J.; Barlow, Joel W.
    Qualitative and quantitative analyses are required to develop Selective Laser Sintering into a viable Manufacturing process. A simplified mathematical model for sintering incorporating the heat tJ;ansfer equation. and the sintering rate equation, but using temperature independent thermal properties, is presented in this paper. A practical result is the calculation of sintering depthdeftned as the depth of powder where the void fraction is less than 0.1 as a function of control parameters, such as the laser power intensity, the laser scanning velocity, and the initial bedtemperature. We derive the general behavior of laser sintering. A comparison of model predictions with laser sinterlng tests is provided.
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    Geometric Modeling for Rapid Prototyping and Tool Fabrication
    (1990) Gursoz, E. Levent; Weiss, Lee E.; Prinz, Fritz B.
    This paper describes the application of a non-manifold geometric modeling environment, NOODLES, to a Rapid Tool Fabrication System. This system integrates stereolithography and thermal spray deposition into a CAD/CAM environment which includes design evaluation tools, robotic spraying, and computer-aided process planning. The level of integration and the number of different models in this system requires geometric representations that can be abstracted at several levels and that can be manipulated over several dimensions. The models in our framework for design, analysis, and fabrication share a single comlnon unifying geometric representation implemented in NOODLES.
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    Contour Following for Scanning Control in SFF Application : Control Trajectory Planning
    (1990) Wu, Ying-Jeng Engin; Beaman, J.J.
    Geometric contour following for scanning control in SFF application is used to refine the boundary ofthe parts for increasing the accuracy or to develop the capability to arrange various scanning directions and paths for improving the part strength. The scanners must be driven to follow the prescribed path as fast as possible, limited by available torques. In this paper the minimum time optimal control problem with specified path and limited control torque is formulated. According to the trade-off between various requirements, a control strategy is studied.
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    A New CAD Model Format For SFF Machines?
    (1990) Darrah, James; Wielgus, Martin
    This paper addresses the issue of a standard input data fonnat for Solid Freefonn Fabrication (SFF) machines. Currently implemented approaches do not address the different aspects of Solid Freefonn Fabrication. This paper will state the requirements from the perspective of the SFF machine designer and make recommendations based on these requirements.
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    ALPHA_I, Remote Manufacturing, and Solid Freeform Fabrication
    (1990) Drake, Samuel H.
    Alpha_l is a nonuniform rational B-spline (NURBs) based solid modeling system that has been developed at the University of Utah over the past 10 years. In addition to being useful in modeling objects that are described by simple rotation and extrusion operations, the real power of Alpha_l is demonstrated in the modeling of complex parts with sculptured surfaces. For the past several years, a major research thrust has been to use Alpha_l to semi-automatically generate process plan information and numerical control code to manufacture mechanical parts directly from the models. A long term goal is to support an on-line remote manufacturing facility for producing prototype parts. Recently, a 3D Systems stereo lithography machine has been added to the advanced manufacturing laboratory. The stereo lithography process and other SFF techniques are of particular interest for supporting a remote manufacturing facility in that these processes are inherently much safer than numerically controlled machining. Special Alpha_l interfaces including a new slicing algorithm are being developed for the SFF machine use. By generating a SFF part directly from its NURBs description, Alpha_l should facilitate the manufacture of complex parts while providing smoother surfaces.
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    Steel-Based Sprayed Metal Tooling
    (1990) Fussell, P.S.; Weiss, L.E.
    A strategy for building sprayed steel tooling by arc spray deposition is discussed in this paper. Depositing steel is crucial for moving sprayed metal toolingfrom prototype applications to superior prototype and production-quality tooling. Tooling is fabricated by spraying onto S\lbStra~S that define the tooling shell shape. In particular, two process issues are addressed: deposition of thick metal shells, and control of oxide content by atomization with inert gases.
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    Selective Laser Sintering of Binary Metallic Powder
    (1990) Manriquez-Frayre, J.A.; Bourell, D.L.
    A selective laser sintering technique has been used to process metal powders and powder blends. Precursor powders include copper, tin, a 70Pb-30Sn solder and their blends. Excessive balling due to surface free energy effects occurred in single layer tests when the laser fluence was sufficient to cause melting of monolithic tin or solder. Improvements in single layer quality were obtained using copper-solder powder blends in a reducing atmosphere. The binary powder layers were characterized metallographically and the effect of processing parameters such as laser fluence and scan speed were assessed. Post-process annealing improved interparticle wetting and part strength. The influence of ZnCl2 flux was investigated when present as a coating in copper-solder blends. Multiple layer tests were performed on the most promising powder blends and the results are presented.
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    Prediction of the Thermal Conductivity of Beds Which Contain Polymer Coated Metal Particles
    (1990) Badrinarayan, B.; Barlow, J.W.
    Structural parts of ceramics or metals can, in principle, be made by laser sintering polymer coated ceramic or metal powders, followed by conventional methods for removing the binder and sintering in ovens. Understanding the laser sintering of coated materials requires knowledge of the behavior of beds containing composite particles. Many correlations for predicting the effective thermal conductivity of a bed of solid particles exist in literature, but little work has been done on beds of coated particles. We coated lead shots(high conductivity) with a styrene acrylic acid copolymer (low conductivity) to study the effect of coating thickness on the thermal conductivity. The thermal conductivity ofthe coated particle·hed was found to •drop rapidly in the beginning·· and then level off with increasing coating thickness. We also developed an equation that yields the equivalent conductivity of a coated spherical particle subjected to axial heat flow. The predicted results with the experimental measurements of bed conductivity obtained by an unsteady state method.
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    Solid Freeform Fabrication by Selective Area Laser Deposition
    (1990) Zong, G.S.; Carnes, R.; Wheat, H.G.; Marcus, H.L.
    Laser chemical vapor deposition is capable of selective area deposition of thin fums at high spatial resolution, and in the present work this advantage was used to perform solid freeform fabrication (SFF). The pyrolytic selective area laser deposition of carbon is studied as a function of the scanning speed, the laser power, and the diameter of the focal spot on the substrate, at different pressures of the acetylene precursor in a gas phase SFF system. Carbon rods and rings have been made. SEM and Raman microprobe were used to characterize the deposits.
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    Modeling of Selective Area Laser Deposition for Solid Freeform fabrication
    (1990) Jacquot, Y.; Zong, S.; Marcus, H.L.
    The results of a theoretical study of the selective area laser deposition process used for Solid Freeform Fabrication (SFF) from gas phase is presented. We show how the deposition profile of carbon deposited via pyrolytic laser chemical vapor deposition using acetylene as the source gas can be computed by taking into account heat transfer, reaction, and mass transfer processes inside the reactor. The two dimensional representation of the related experimental variables are used to describe the substrate temperature, carbon deposit, and acetylene concentration in the process. The parameters describing these processes are estimated.
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    Design of a Solid Freeform Fabrication Diamond Reactor
    (1990) Thissell, W.Richards; Tompkins, James; Marcus, Harris L.
    Solid Freeform Fabrication (SFF) has progressed from the visualization aided stage of computer aided designs (CAD) to rapid prototyping of structural parts. Among the promising techniques for producing structural prototypes is the technology ofchemical vapor deposition (CVD) ofpolycrystalline diamond. This paper discusses the thermodynamic and kinetic theories that suggest that structural diamond may be rapidly deposited at rates approaching 1 mmJhr from the vapor phase at metastable thermodynamic conditions. The design of a reactor that will produce structural diamond prototypes is discussed. This reactor combines downstream microwave plasma enhanced chemical vapor deposition (DMWPECVD) with a scanned CO2 laser that locally heats the substrate to diamond deposition temperatures. The input:Fases are H2, 02' CH4, and Ar. The operating pressure range of the reactor is 1 x 10- to 7 x 102 Torr. The reactor is designed for in situ determination of deposit thickness while deposition occurs as well as having the capacity of fitting on an existing resonance enhanced multiphoton ionization time of flight mass spectroscopy (REMPITOFMS) apparatus that will allow for plasma diagnostics immediately above the heated substrate. Plasma diagnostics will be employed to determine the active metastable species that results in diamond deposition so that optimization can be made ofthe operating parameters to maximize diamond selectivity and deposition rate.
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    Three Dimensional Printing: Rapid Tooling and Prototypes Directly from CAD Representation
    (1990) Sachs, Emanuel; Cima, Michael; Cornie, James
    Industrial productivity and competitive success depend on fast, efficient product development technologies. The flexible manufacture of tooling and mechanical prototypes can greatly reduce the time required for bringing a product to market. Tooling frequently dominates manufacturing time and cost, thereby determining the minimum economic batch size for a given process. Tooling can be extremely complex and is generally one-of-a-kind, requiring much human attention to detail. As a result, fabrication of tooling for such processes as injection molding or lost wax casting, commonly requires several months of work. Three Dimensional Printing offers an alternative to conventional options which do not adequately answer the demands for rapid prototyping and speedy, low-cost production of tooling.
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    Selective Laser Sintering of Ceramic Materials
    (1990) Lakshminarayan, Uday; Ogrydiziak, Stan; Marcus, H.L.
    This paper will focus on efforts to develop the alumina - ammonium phosphate material system for Solid Freeform Fabrication. When the powder mix is irradiated with a laser beam, ammonium phosphate ( m.p. """ 190 0 C ) melts and forms a glassy phase between the alumina grains. The "green part" obtained by laser processing is then subjected to secondary heat treatment to optimize the properties of the final composite. The effect of various material, laser and machine parameters on the density, strength, surface finish and microstructure of the final part are described. One of the applications for selective laser sintering is its use in directly manufacturing ceramic molds for the investment casting process. We will describe some of the the results we have obtained so far in fabricating composite ceramic molds directly and using them to cast metals.
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    Microencapsulation of Finely Divided Ceramic Powders
    (1990) Vail, N.K.; Barlow, J.W.
    Polymer coated alumina particles have been prepared by spray drying alumina powder with a polymer emulsion. Powders containing a maximum of 50% wt. were obtained. The coated particles were compared to mixtures of alumina and polymer. Oven sintering tests show the coated material to compact more than the mixed and pure polymer materials. Strong, well defined parts with layer thicknesses of 0.002" were produced from both coated and mixed materials by the Selective Layer Sintering process.
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    Solid Freeform Fabrication An Advanced Manufacturing Approach
    (1990) Bourell, D.L.; Beaman, J.J.; Marcus, H.L.; Barlow, J.W.; Bourell, D.L.; Beaman, J.J.; Marcus, H.L.; Barlow, J.W.