Browsing by Subject "Department of Mechanical Engineering"
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Item Adaptive Laminated Machining for Prototyping of Dies and Molds(1992) Vouzelaud, F.A.; Bagchi, A.Adaptive laminated machining is the fusion of slicing a solid model into layers and producing parts by CNC milling machines. Unlike other solid freeform fabrication processes which create the part by addition of material, adaptive laminated machining can create solid parts by selectively removing in layers. The research issues and practical limitations on shape and manufacturability are thus different from other processes. However, the biggest advantage is the ability to obtain a solid metal part such as a die or a mold directly. In this paper, the concept of this technique, and initial results and parts produced in Clemson will be presented. In addition, future research needs and issues will be discussed.Item The Application of an Artificial Body Force to the Selective Laser Sintering Process(1992) Melvin, Lawrence S. III; Beaman, J.J.An artificial body force generated by a magnetic field is applied to the green powder bed of a ferromagnetic powder during the Selective Laser Sintering process. Preliminary experiments and theory are formed to determine whether the artificial body force is beneficial to the Selective Laser Sintering process and if it is usable within that process. Several applications are discussed including microgravity situations and two phase sintering processes. It is determined that the magnetic body force is beneficial to the Selective Laser Sintering process.Item Application of Factorial Design in Selective Laser Sintering(1992) Deng, Xioaming; Beaman, Joseph J.Selective Laser Sintering (SLS) is a complex process involving many process parameters. These parameters are not all independent. A factorial design technique is utilized to study the effects of three main process parameters, laser power, laser beam scanning speed, and powder packing density as well as their interactions on the sintering depth and fractional density. The results of this investigation provide useful information for the further experimental analysis of the process parameters and for selecting suitable parameters for SLS process.Item Computer Aspects of Solid Freeform Fabrication: Geometry, Process Control, and Design(1993) Crawford, Richard H.Solid Freefonn Fabrication (SFF) is a class of manufacturing technologies aimed at the production of mechanical components without part-specific tooling or process planning. Originally used for creating modelsfor visualization, many industrial users of SFF technologies are realizing the greater potentialofSFF as legitimate manufacturing processes for producing patterns and, in some cases, functional.parts. Thus, SFF is becoming an important aspect of the product realization process in these industries. Solid Freefonn Fabrication arose from the dream of "push-button" prototyping, in which solid reproductions of three-dimensional geometric models are created automatically under computer control. Perhaps more than any other class of manufacturing technologies, computer software development has been an integral part of the emergence of SFF. As SFF technologies evolve toward the ability to create functional parts, computer issues gain more importance. This paper discusses three aspects of software design for SFF: processing of geometric data, global and local control of SFF processes, and computer-based analysis and design for SFF manufacturing. The discussion of geometric processing issues focuses on accuracy and completeness of input models, and the algorithms required to process such models. The interplay between the physics of SFF processing and the desired output geometry is discussed in terms of the development of model-based control algorithms for SFF. These two areas, geometric processing and control, are necessary for the practical implementation of any SFF technology. However, for SFF to realize its potential as an alternative for manufacturing functional parts, engineers must be provided with analysis and design tools for predicting mechanical properties, ensuring dimensional accuracy, choosing appropriate materials, selecting process parameter values, etc. For each of these three different but related areas of software design, the state-of-theart is assessed, contemporary research is summarized, and future needs are outlined.Item Design of a High Temperature Process Chamber for the Selective Laser Sintering Process(1992) McWilliams, John; Hysinger, Christopher; Beaman, J.J.Item Design of a High Temperature Workstation for the Selective Laser Sintering Process(1991) Das, Suman; McWilliam, John; Wu, Benny; Beaman, J.J.Item 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.Item Direct Generation of Contour Files from Constructive Solid Geometry Representations(1993) Guduri, SashidharGeometry processing for layer-based Solid Freeform Fabrication consists of at least two steps: slicing the geometry to obtain the part contours for each layer, and scan-converting the layers for laser scanning (or other device-dependent in-layer processing). This paper discusses the generation of contour files directly from Constructive Solid Geometry (CSG) representations for the Selective Laser Sintering process. Previous work at The University of Texas focused on slicing CSG representations composed of quadric primitives. This paper extends previous work at UT to include the torus, a fourth degree surface, as one of the CSG primitives. Slicing a torus results in a fourth degree equation in two variables, which represents a curve in two-dimensional real space. For. some special cases, this fourth degree equation may be sub-divided into two second degree equations. For the cases where the fourth degree equation cannot be sub-divided, a method is presented to approximate the fourth degree curve with second degree curve segments.Item Direct Selective Laser Sintering of High Temperature Materials(1992) Zong, G.; Wu, Y.; Tran, N.; Lee, I.; Bourell, D.L.; Beaman, J.J.; Marcus, H.L.Selective Laser Sintering (SLS) involving a coexisting liquid and particulate solid during the SLS processing can be used to produce freeform parts directly with high temperature materials. Factors such as scanning laser power density, residence time, scan line spacing, the interfacial energies between the liquid and solid phases, powder bed biasing temperature, and sintering atmosphere greatly affect the microstructure evolution in the SLS process. Direct SLS of high melting temperature mixed powder materials was demonstrated using a 1.1 kW C02 laser SLS system. The relationship between the microstructures and the process parameters will be described.Item The Electrostatic Application of Powder for Selective Laser Sintering(1991) Melvin, Lawrence S. III; Beaman, J.J.Item An Evaluation of the Mechanical Behavior of Bronze-NI Composites Produced by Selective Laser Sintering(1993) Agarwala, Mukesh K.; Bourell, David L.; Wu, Benny; Beaman, Joseph J.Mechanical properties of Bronze-Nickel composites produced by Selective Laser Sintering (SLS) were evaluated by constant displacement tension tests. These were studied as a function of SLS process parameters - laser power density, scan speed, scan spacing, scan direction and layer thickness. The strength data was then correlated to the microstructure and the part bulk density. To further enhance the part densities and the mechanical properties, post-SLS sintering was studied. The relationships between SLS process parameters, post-SLS sintering parameters and the resulting microstructures, part bulk density and the mechanical properties will be described.Item Indirect Metal Composite Part Manufacture Using the SLS Process(1993) Tobin, James R.; Badrinarayan, B.; Barlow, J.W.; Beaman, J.J.As a near term alternative process to direct sintering, an intermediate polymer binder is combined with powder to produce green preforms with the Selective Laser Sintering (SLS) process. To produce parts with desirable strength dimensional control, the binder is gradually removed from the green preform (obtained from the SLS process), and the remaining form is lightly bonded. This porous part then infiltrated. Final part density, shrinkage, and strength data are presented. An injection mold insert was fabricated from this material and used to mold PMMA, polyester, and polycarbonate parts. To date, the mold insert 176 shots at injection to 35,000 and melt temperatures up to 300°C.Item Laser Tracking Control Implementation for SFF Applications(1992) Wu, Ying-Jeng Engin; Beaman, Joseph J.From a three-dimensional computer graphic model, Solid Freeform Fabrication produces solid objects directly without special tooling and human handling. In order to increas process productivity and accuracy, a time-efficient laser tracking control technique is needed. Based on the minimum time optimal control solution, the desired laser scanning control system is designed and implemented. To obtain uniform solidification during timeefficient tracking which has variable speed, laser power intensity is also controlled in real time by an acousto-optic modulator.Item Machine Issues Associated with Solid Freeform Fabrication(1992) Beaman, Joseph J.Before we begin a discussion of machine issues it is important that we categorize exactly what we mean. There are differences between the design of a research piece of equipment as compared to a commercial piece of equipment. A research piece of equipment has to have the flexibility to demonstrate a success pattern. A commercial piece of equipment, on the other hand, assumes that you have a stable platform and you are now trying to assess how broad a success path you have (Figure 1). In fact, you are trying to make that path as broad as possible so that the machine will not fail and will always work the same way. This particular talk, and my expertise, is much more along the lines of design of a research piece of equipment. What I will be talking about today are machine issues associated with developing a success path in Solid Freeform Fabrication. The machines we will be talking about have to have the flexibility to operate in a wide variety of ways with a wide variety of experiments.Item A Method to Generate Exact Contour Files for Solid Freeform Fabrication(1992) Guduri, Sashidhar; Crawford, Richard H.Existing methods to create contour files generate a polygonal approximation of the contours instead of an exact representation. This paper presents a method to generate exact contours from Constructive Solid Geometry (CSG) representations. The method preserves the accuracy of the contour files provided the primitives used to generate the CSG tree are polygonal or quadric objects. Due to the inclusion of quadric objects into the primitive set an additional effort to solve for the intersection points between two quadric curves is required. The paper also presents a method to convert piecewise quadratic contours to toggle point files for raster scanning solid freeform fabrication processes.Item Parametric Analysis for Selective Laser Sintering of a Sample Polymer System(1992) Deng, Xioaming; Zong, Guisheng; Beaman, Joseph J.Item The Physics of Digital Microfabrication with Molten Microdrops(1993) Gao, Fuquan; Sonin, Ain A.Precise deposition of molten microdrops under controlled thermal conditions provides a means of 3D "digital microfabrication" , microdrop by microdrop, under complete computer control, much in the same way as 2D hard copy is obtained by ink-jet printing. This paper describes some results from a study of the basic modes of microdrop deposition and solidification (Gao & Sonin, 1993). The conditions required controlled deposition are discussed, and some experimental results and theoretical analyses are given for various basic deposition modes. These include columnar (Le. drop-on-drop) deposition at low and high frequencies, sweep deposition of continuous beads on flat surfaces, and repeated sweep deposition for buildup of larger objects or materials.Item Powder Layer Position Accuracy in Powder-Based Rapid Prototyping(1993) John Lee, Sang-Joon; Sachs, Emanuel; Cima, MichaelItem Preliminary Experience with Selective Laser Sintigrapbic (SLS) Models of the Human Temporal Bone(1992) Levy, Richard A.; Guduri, Sashidhar; Crawford, Richard H.To assess the accuracy of three-dimensional models of the human temporal bone generated from computed tomographic (CT) data.Item Process Control System for a High Temperature Workstation performing the Selective Laser Sintering Process(1992) Das, Suman; Crawford, Richard H.; Beaman, J.J.Thispaper describes the design and implementation ofa Computer Process Control System for a High Temperature Workstation performing Selective Laser Sintering of metal and .ceramic powders. As compared to our previous machine [1], the increased complexity and sophistication .of·the.new workstation [21 requires a variety of measurement and control devices which are.interfaced to a process controlcomputer. Among these are a. gas analyzer, a data logger, a step motor controllerandaCNC controller. This process control system incorporates a XView ( aX Window System Toolkit) based Graphical User Interface which allows the user.to set and change process parameters on-line as well as receive graphical feedback onthe process.