1997 International Solid Freeform Fabrication Symposium

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Proceedings for the 1997 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Eighth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 11-13, 1997, was attended by 200 national and international researchers. Papers addressed SFF issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. The continued growth in the research, application and development of SFF approaches was readily apparent from the increased participation over previous years and the diverse domestic and foreign attendees from industrial users, SFF machine manufacturers, universities, and government. The excitement generated at the Symposium reflects the participants' total involvement in SFF and the future technical health of this growing technology. The Symposium organizers look forward to its being a continuing forum for technical exchange among the expanding body of researchers involved in SFF.

The Symposium was again organized in a manner to allow the multi-disciplinary nature of the SFF research to be presented coherently, with various sessions emphasizing computer issues, machine topics, and the variety of materials aspects of SFF. We believe that documenting the constantly changing state of SFF art as represented by these Proceedings will serve both the people presently involved in this fruitful technical area as well as the large flux of new researchers and users entering the field.

The editors would like to extend a warm "Thank You" to Glorya Gutchess for her detailed handling of the logistics of the meeting and the Proceedings, as well as her excellent performance as registrar and problem solver during the meeting. We also acknowledge the support efforts of Cindy Pflughoft throughout. We would like to thank the organizing committee, the session chairmen, the attendees for their enthusiastic contributions, 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 SFF community in organizing the Symposium. We also want to thank ONR through Grant No. NOOOI4-97-1-0453, DARPA, and The Minerals, Metals and Materials Society and the University of Connecticut at Storrs for co-sponsoring the Symposium with the Mechanical Engineering Department, Laboratory for Freeform Fabrication and the Center for Materials Science and Engineering at the University of Texas at Austin.


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    1997 International Solid Freeform Fabrication Symposium Table of Contents
    (1997) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Reaction Heat Effect On Initial Linear Shrinkage of Sterelothigraphy Resins
    (1997) NARAHARA, Hiroyuki; TANAKA, Fumiki; KISHINAMI, Takeshi; IGARASHI, Satoru; SAITO, Katsumasa
    In the industrial use ofthe Stereolithography, the precision is always a problem. Basic phenomenon of the solidification shrink has not suffiCiently investigated This study aims at clarifying the initial linear shrinkage ofcured resin in a minute volume. Experimental equipment has been developed which measures the time history of the single strand in situ in a stereolithography machine. Analysis model about the time history of a minute volume linear shrinkage has been shown using with the measured shrinkage of a cured line segment. The relation between the time history ofthe linear shrinkage and the temperature was measured and the shrinkage in the minute volume after irradiation has been caused by the temperature variation
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    Modeling of Mechanical Behavior of SLA Parts
    (1997) Wu, Zhanping; Ogale, Amod A.; Ahzi, Said; Paul, Frank W.; Hunt, Elaine
    In recent years, important efforts have been focused on producing functional parts using Stereolithography Apparatus ( SLA ). One of the applications is the development of rapid polymer tooling such as dies for injection molding. For these applications, optimal thermal as well as mechanical properties are of significance. In this paper, the mechanical behavior of the cured resin SL5170 is discussed by use of an elastic-viscoplastic material model. Uniaxial compression tests at different deformation rates are conducted. The stress-strain curves of these tests are predicted by the model, and comparisons of these results with experiments show good agreement.
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    On dimensional stabilities: Modeling of the Bonus-Z during the SLS Process
    (1997) Papadatos, Alexandre L.; Ahzi, Said; Deckard, Carl R.; Paul, Frank W.
    This work is a first step towards the prediction of the dimensions and thermomechanical properties ofparts made with the Selective Laser Sintering (SLS) technology. An important variation of the dimensions is found in the Z-direction of the build. This phenomenon is known as the "Bonus-Z" where material properties differ from those in the rest of the part due to a non-homogeneous sintering. The focus of this work is the characterization and the modeling of the bonus-Z phenomenon, by relating it to the energy input. The polymer powder used in this study is polycarbonate.
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    Simulation Of Coarsening During Laser Engineered Net Shaping
    (1997) Tikare, Veena; Griffith, Michelle; Schlienger, Eric; Smugeresky, John
    Laser Engineered Net_Shaping, otherwise known as LENSTM, is an advanced manufacturing technique used to fabricate complex near net shaped components directly from engineering solid models without the use of dies or machining. The ultimate objective ofthis project is to develop predictive simulation capability which will allow the LENSTM processors to determine fabrication conditions given the material, shape, and application ofthe final part. In this paper, we will present an incremental achievement to meeting the ultimate goal, a model capable ofsimulating the coarsening ofmicrostructural features under the unique thermal history to which a LENSTM part is subjected during processing. The simulation results show how grains ofvery different shapes and sizes form within the same deposition line. They also show that relatively minor changes in the dynamic temperature profile results in microstructures with vastly different characteristics. The implications ofthis work for LENSTM fabrication is that controlling the temperature profile is essential to tailoring the microstructure of a component to its application.
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    Thermal Analysis Of Fused Deposition
    (1997) AtifYardimci, M.; Hattori, Takeshi; Guceri, Selcuk I.; Danforth, Stephen C.
    Fused Deposition processes involve successive melting, extrusion and solidification of thermoplastic polymer melts. Fluid mechanics and heat transfer of neat or particle-filled polymeric melts, viscoelastic deformation and solidification ofthe roads that are being produced, and repetitive thermal loading of the growing part are important physical processes that control the final quality of the part. Previous computational process models investigated deposition and cooling processes for single and multiple filaments. In the current study, complimentary computational models are presented for the extrusion phase of the process. Impact of liquefier and nozzle design on thermal hardware behavior and operational stability has been quantified. Also a detailed study of temperature field near the vicinity of deposition point is presented with particular emphasis on dimensional analysis and deposition ofmultiple material systems.
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    A Thermal Model For Laminated Object Manufacturing (LOM)
    (1997) Flach, Lawrance; Klostennan, Donald A.; Chartoff, Richard P.
    A thennal model for Laminated Object Manufacturing (LOM) has been developed. The model is based on 3-dimensional transient heat conduction in a rectangular geometry LOM part. Heat transfer from the heated roller to the laminated part as well as heat loss to the surroundings and the base plate are considered. It allows calculation of the transient temperature distribution within the part during the application of a new layer as well as during other periods of the LOM build cycle. To verify the model performance, thennocouples were embedded every 4th layer in a 20-layer ceramic part while it was being built on a standard LOM-2030. The model predictions are in excellent agreement with the measured temperature profiles. In addition to explaining the observed thennal behavior ofLOM parts, model predictions also have direct application to on-line control ofthe part temperature during the build process, to be discussed herein.
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    The Use of VRML to Integrate Design and Solid Freeform Fabrication
    (1997) Wang, Yanshuo; Dong, Jian; Marcus, Harris L.
    The Virtual Reality Modeling Language (VRML) was created to put interconnected 3D worlds onto every desktop. The 3D VRML format has the potential for 3D fax and TeleManufacture. An architecture and methodology of using VRML format to integrate a 3D model and Solid Freeform Fabrication system are described in this paper. The prototype software discussed in this paper demonstrates the use of VRML for Solid Freeform Fabrication process planning. The path used from design to part will be described.
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    An Integrated Software System for Process Planning for Layered Manufacturing
    (1997) Marsan, Anne L.; Allen, Seth; Kulkarni, Prashant; Dutta, Deba
    An integrated process planning system for layered manufacturing (LM) reduces the time between design and part fabrication and improves the quality of the final part. Process planning for most LM processes includes part orientation, support structure generation, slicing, and path planning. In this paper we describe an integrated process planning system we are developing. Our software accommodates both novel and traditional design models as input, and supports a variety of LM processes. The modules described in this paper include Solid Builder Module, which generates a solid model from design data such as medical images, surface functions, or digital elevation models; Orientation Module, which determines the optimal build orientation of a part and automatically generates the support structures required; and Adaptive Slicing Module, which adaptively slices the part.
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    Optimising Build Parameters and Hatch Style for Part Accuracy in Stereolithography
    (1997) ONUH, S.O.; HON, K.K.B.
    A detailed study of the effects of layer thickness, hatch spacing, hatch overcure depth, and hatch fill cure depth on the quality of the StereoLithography (SL) product was carried out using acrylic based resin. Taguchi Method was used for analysing all experimental results. The ANOVA and the Signal-to-noise ratio (SIN) results were used to select the optimum parameters and the appropriate factor levels for further experiments. A new hatch styIe with an optimum layer thickness is proposed for the build process with minimum geometrical distortion.
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    CAD and Control Technologies for Computer-Aided Manufacturing of Laminated Engineering Materials
    (1997) Choi, Sangeun; Hebbar, Ravi; Zheng, Yong; Newman, Wyatt S.
    This paper presents recent progress in software, material handling and tangent-cutting control in support of Computer-Aided Manufacturing of Laminated Engineering Materials(CAM-LEM). Progress in CAD focuses on the definition of a new layered file format for describing 3-D solids in terms of thick slabs with ruled-surface edges. For material handling, we present new algorithms for automatic generation of mask hole patterns used in selective-area vacuum gripping, which is required for our laminated assembly process. Finally, we present recent results of object fabrication using thick-slab, tangent-cut layers
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    Validation of Rapid Prototyping Material for Rapid Experimental Stress Analysis
    (1997) Schley, C.; Smith, G.F.
    The paper will detail the validation work carried out on various Rapid Prototyping (RP) materials to determine their suitability for the application of Thermoelastic Stress Analysis. The overall objective is to drastically reduce the product design cycle, by providing "real experimental data" for correlation with Finite Element Analysis (FEA), prior to any expensive manufacturing process. In order to achieve this the homogeneity of the Rapid Prototyping material has to be established to ensure a valid transfer of results from model to actual part.
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    Build Style Decision Support for Stereolithography
    (1997) McClurkin, Joel E.; Rosen, David W.
    When building parts in a stereolithography apparatus (SLA), the user is faced with many decisions regarding how the part will be built. The quality of the build can be controlled by the user via changing one of several build style variables, including part orientation, cross sectional layer thickness, and laser hatch density. A user will probably have preferences for the part build (Le., accuracy or speed), but may not understand how to vary the build style variables to produce the desired results. A method based on response surface methodology and multi-objective decision support is described in this paper for relating build goals to three build style variables, and the use ofthese relationships in providing decision support for building a part on a SLA. The method is applied to the build style of a circuit breaker handle.
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    A data format providing side wall orientation and adaptive slicing for use in stepless rapid prototyping
    (1997) Fang, Wei; Siang Ngooi, Chan; Gong, Haiqing
    Current Rapid Prototyping systems mainly use 2D layers building techniques that result in the 'staircase' effect on slanted surface. A new method has been developed to eliminate the 'staircase' effect and to improve the surface quality by extending the 2D layers to 3D layers building. In this approach, a new data format, Layer Transfer Interface (LTI), is introduced to generate layers having slanted side wall. It provides a faster slicing algorithm and accurate reconstruction of 3D objects. This format is independent of any particular RP machines. Furthermore, adaptive slicing has been achieved using this format and implemented on a fiveaxis milling RP system.
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    Solid Model Creation for Materially Graded Objects
    (1997) Kumar, Vinod; Dutta, Debasish
    Materially graded objects are objects composed of different constituent materials and could exhibit continuously varying composition and/or microstructure [1][2]. Such continuous changes results in gradation in their properties and distinguish them from objects made of conventional composites. They are also known as heterogeneous objects, functionally graded/gradient materials (FGM) and multi-material objects/structures [1]. In this paper, we use the terms "materially graded objects" and "heterogeneous objects" interchangeably. Recently, heterogeneous objects have found use in several engineering applications. The fabrication process that has shown potential to manufacture heterogeneous objects is called Solid Freeform Fabrication (SFF), also known as Layered Manufacturing (LM) [3][4]. SFF is a material deposition process in which the material deposition can be controlled to vary the material composition throughout an object, thus fabricating a materially graded object. All SFF technologies are computer-based and require the CAD model ofthe object to be manufactured. However, current CAD systems are capable of representing only the geometry/topology information. Therefore, heterogeneous objects are fabricated using SFF by manually feeding the material information along with the geometry data. This is a cumbersome process and leads to the under-utilization ofthe SFF process. An assessment of existing representations for SFF is presented in [5] highlighting the need for CAD models which represent material information along with the geometry data of the object.
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    Reverse Engineering: Practical Considerations for Rapid Prototyping
    (1997) Griffin, Alair; McMillin, Scott; Griffin, Curtis; Knox, Dr. Charles
    It is now possible to generate threedimensional (3D) solid models of extremely complicated systems from which full plastic replicas can be generated using a variety of rapid prototyping technologies. The cycle time has been reduced to several hours, where it previously took months to produce a comparable prototype. The process of taking a design into the 3D environment, whether UNIX-or PC-based, is getting easier and fairly straightforward.The design engineer interested in producing a 3D model from unique data sets such as computer tomography (CT) or magnetic resonance (MR) image data is particularly concerned with time, cost, accuracy, and conversion problems. This paper presents an approach that Lone Peak Engineering, Inc. (LPE) has used that allows them to successfully handle CT and MR data for reverse engineering (RE).
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    Reverse Engineering: Algebraic Boundary Representations to Constructive Solid Geometry
    (1997) Buchele, S. F.; Ellingson, W. A.
    Recent advances in reverse engineering have focused on recovering a boundary representation (b-rep) of an object, often for integration with rapid prototyping. This boundary representation may be a 3-D point cloud, a triangulation of points, or piecewise algebraic or parametric surfaces. This paper presents work in progress to develop an algorithm to extend the current state of the art in reverse engineering of mechanical parts. This algorithm will take algebraic surface representations as input and will produce a constructive solid geometry (CSG) description that uses solid primitives such as rectangular block, pyramid, sphere, cylinder, and cone. The proposed algorithm will automatically generate a CSG solid model of a part given its algebraic b-rep, thus allowing direct input into a CAD system and subsequent CSG model generation.
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    Using adaptive ruled layers for Rapid Prototyping: principles and first results
    (1997) de Jager, P.J.; Broek, J.J.; Vergeest, J.S.M.
    Current 2.5D layered rapid prototyping has as disadvantage the staircase effect, requiring thin layers to be used to achieve a reasonable accuracy. Slices with inclined outer surfaces can be constructed using linear interpolation between adjacent contours, resulting in ruled slices. A methodology to approximate a given model geometry within a specified accuracy using ruled slices and an adaptive layer thickness is described. This involves matching successive contours and analysing the geometry for curvature and inclination to calculate allowed layerthicknesses. First results show a significant reduction in the number of layers when compared to adaptive slicing using 2.5D layers. A proof-of-concept software, the Delft University of Technology Improved Slicer (DUTIS) has been developed to perform the adaptive slicing using either 2.5D or ruled layers allowing a comparison between the two alternative methods.
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    An Analysis Technique for Layered Manufacturing Based on Quasi-Wavelet Transforms
    (1997) Lee, Cheol H.; Thomas, Charles L.
    An analysis technique based on the Wavelet transform (WT) has been recently introduced that allows the spatial frequency content of objects produced by layered manufacturing (LM) techniques to be interpreted in terms ofmanufacturable features. (Lee and Thomas, 1997) Using Haar's wavelet as a basis function, layers with vertical edges are modeled exactly. Using analysis, a 3D model can be transformed, filtered, and inverse transformed resulting in an image ofthe part as it would look if constructed from layers of a specific thickness. In order to extend this analysis to construction techniques using higher order edges (ruled surface edges or curved edges), the quasi-wavelet transform (QWT) is introduced. QWT analysis is conceptually the same as WT analysis, except that the basis function can be selected by the user, allowing exact analysis of layered manufacturing techniques using higher order construction algorithms. This work is supported by a grant from the University ofUtah Research Foundation.