Browsing 1990 International Solid Freeform Fabrication Symposium by Title
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Item1990 Annual International Solid Freeform Fabrication Symposium Table of Contents(1990) Laboratory for Freeform Fabrication; University of Texas at Austin Item1990 International Solid Freeform Fabrication Symposium Table of Contents(1990) Laboratory for Freeform Fabrication and University of Texas at Austin ItemALPHA_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. ItemA 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. ItemContour 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. ItemDesign 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. ItemGeometric 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. ItemMicroencapsulation 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. ItemModeling 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. ItemA New CAD Model Format For SFF Machines?(1990) Darrah, James; Wielgus, MartinThis 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.