1993 International Solid Freeform Fabrication Symposium

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Proceedings for the 1993 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

This Proceedings of the Fourth Solid Freeform Fabrication Symposium, held at The University of Texas in Austin on August 9-11, 1993, reaffirms the dynamic nature of the research area. The interest shown by researchers over the wide range of disciplines and sub- disciplines that make up Solid Freeform Fabrication (SFF) highlights this technical Symposium. The speakers addressed problems in computer software, in machine design, materials synthesis and processing, and SFF in integrated manufacturing. The exponential growth in the research, application and development of SFF approaches was readily apparent from the attendees from industrial users, SFF machine manufacturers, universities, and government. This Symposium is the first where real progress toward structurally sound samples and parts was demonstrated as SFF moves from "feelie" to "non-structural" to "structural" real parts over a range of materials. This advancement in the state-of-the-art of SFF will continue to drive the exponential growth of the area. The excitement amongst the Symposium participants will continue to serve as the catalyst for the continued growth and the availability of Solid Freeform Fabrication. The Symposium organizers look forward to its being a continued source of technical exchange among the growing body of researchers involved in SFF.

The Symposium was organized in a manner to allow the multi-disciplinary nature of the SFF research to be presented coherently, with various sessions emphasizing computer aspects, machine topics, and the variety of materials aspects of SFF. Application-related efforts were scattered throughout the Symposium. To avoid parallel sessions a poster session was organized, and the panel session on SFF was held in the evening, after a visit with Texas barbecue. The dynamic panel discussion on Future Directions in SFF was led by Marshall Burns, Michael J. Cima, Tom Latham, Greg Sanders and Joel W. Barlow. The written versions of the presented papers are incorporated into these Proceedings. The editors would like to thank the speakers for their timely delivery of the manuscripts that expedited the publication of these Proceedings. The constantly changing state of the SFF art as represented by these Proceedings will serve both the people. presently involved in this fruitful area as well as new researchers and users coming into Solid Freeform Fabrication.

The editors would also like to extend a warm thank you to Renee Loyless-May for her extensive efforts in the detailed handling of the logistics of the meeting and the Proceedings. We would also like to thank the organizing committee, the speakers, the session chairmen, panel members, and the attendees for their enthusiastic contributions. 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. N00014-93-1-0371, ARPA, and The Minerals, Metals and Materials Society for co-sponsoring the Symposium as well as DTM Corporation for hosting the reception.

Organizing Committee: Dick Aubin, United Technologies; Joel W. Barlow, The University of Texas at Austin; Joseph J. Beaman, The University of Texas at Austin; David L. Bourell, The University of Texas at Austin; Robert L. Brown, The Gillette Company; William Coblenz, ARPA; Richard Crawford, The University of Texas at Austin; Samuel Drake, University of Utah; Steven Fishman, Office of Naval Research; Harris L. Marcus, The University of Texas at Austin; Fritz Prinz, Carnegie Mellon University; Emanuel Sachs, Massachusetts Institute of Technology; Greg Sanders, General Motors Corporation; Sean O'Reilly, Ford Motor Company; Ralph Wachter, Office of Naval Research; Michael Wozny, Rennselaer Polytechnic Institute

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1993 International Solid Freeform Fabrication Symposium Table of Contents
(1993) Laboratory for Freeform Fabrication and University of Texas at Austin
Automated 4 Axis Adaptive Scanning with the Digibotics Laser Digitizer
(1993) Koch
The DIGIBOT 3D Laser Digitizer is a high performance 3D input device which combines laser ranging technology, personal computing, and Microsoft Windows in an attractive desktop package. With its full four-axis scanning capabilities, the DIGIBOT provides a simple, accurate, and quick way to copy or inspect complex, sculpted surfaces. The DIGIBOT provides an effective solution for many industrial and academic problems involving 3D design, inspection, replication, analysis, and visualization/animation. By measuring sequential points and producing a standard list of x/y/z coordinates, the DIGIBOT interfaces to any CAD/CAM/CAE imaging or animation software that reads 3D points, contours, or triangular facets.
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.
Control Parameters and Materials Selection Criteria for Rapid Prototyping Systems
(1993) Comb, James W.; Priedman, William R.
Since the introduction ofrapid prototyping technology as a tool for time compression and concurrent engineering in the design and manufacturing process, many enhancements and refinements have been made based on the experience ofusers and manufacturers ofrapid prototyping equipment. These improvements contribute significantly to faster production of quality output from rapid prototyping systems. There are diverse control and material selection parameters that affect prototype models built using the Fused Deposition Modeling (FDM®) process. This paper reviews the role of several ofthese parameters in the process. Data will be presented to help the user choose the appropriate material for specific applications including density, tensile stiffhess, flexural stiffhess, tensile strength, flexural strength, tensile ductility, shock resistance, and hardness.
Development of Nanocomposites for Solid Freeform Fabrication
(1993) Manthiram, A.; Chi, F.; Johnson, F.; Birmingham, B.R.; Marcus, H.L.
Nanocomposites in which the constituents are mixed on a nanorneter scale can provide important advantages in the Selective Laser Sintering (SLS) and Selective Laser Reactive Sintering (SLRS) processes. The larger surface area and grain boundaries in the nanocolnposites compared to that in the conventional microcomposites are expected to enhance the solid state diffusion during laser irradiation as well as during any other subsequent processes. Our strategy is to design and develop nanocomposites in which one nanosize cOlnponent has a lower melting point than the other nanosize component, either of which can serve as the matrix phase. The nanoscale dispersion of the low melting component can aid the sintering process during SLS or SLRS. Nanocomposite powders of AI203-COOx, Ab03-NiO, A1203-CO and A1203-Ni have been synthesized by sol-gel processing and are evaluated by SLS.
Direct Generation of Contour Files from Constructive Solid Geometry Representations
(1993) Guduri, Sashidhar
Geometry 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.
Direct Laser Sintering of Metals
(1993) Carter, William T.; Jones, Marshall G.
The use of a directed laser bealn source to selectively sinter multiple layers of binderless metal powder for the purposes of rapid prototyping is described. The work in this paper is restricted to -325 mesh iron powder, which was sintered using a C\V 50 W Nd:YAG laser to approximately 3.5% density. A subsequent post-treatlnent was perfornled to achieve a fully dense saulple. It is envisioned that such a system can be used to manufacture functional metallic prototypes directly from CAD without part-specific tooling.
Drying of Colloidal Binder Infiltrated Ceramic Green Parts Produced by Selective Laser Sintering™
(1993) Glazer, M.; Vail, N.K.; Barlow, J.W.
Colloidal ceramic binders have been used to strengthen ceramic green shapes produced by Selective Laser Sintering. This paper focuses on the effectiveness of the colloid infiltration with respect to the physical properties of the colloidal binder. Mass gains, strength gains, and dimensional changes resulting from infiltration were monitored. Controlled drying experiments were conducted to predict the factors influencing drying times for complex shapes.
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.
An Experimental Study of the Parameters Affecting Curl in Parts Created Using Stereolithography
(1993) Horton, Leslie; Gargiulo, Edward
Fabrication of Ceramic and Metal Matrix Composites From Selective Laser Sintered Ceramic Preforms
(1993) Deckard, Lucy; Claar, T. Dennis
This paper will discuss the tool~less fabrication of functional advanced comJX>sites by infusion of a ceramic or metal matrixinto Selective Laser Sintered(SLS) porous ceranU~preforms using Lanxide'spatentedmatrix infusionproc;esses. The fabri~ationofJX>rous preformS of particulate cerami~sby SLS atthe University ofTexas at Austin is described in a companion paper. The PRlME}(TI4 pressureless metal infi1trationp~ss was used to infiltratesites withoutthe use of tooling. Also, SiC I~03 ceramic matrix comJX>sites were fabricated using the DIMO}(TI4 directed metal oxiJation process to grow an Al20 3 matrix into porous SiC particulate SLS preforms. Measured properties and microstructures of the resulting composites will be presented and compared to similar comJX>sites made using conventionally fabricated preforms. The rapid prototyping of a SiCiAIMMC electronic power package to near~net shape from an SLS preform will also be describeQ.
FFF at Ford Motor Company
(1993) O'Reilly, Sean B.
Ford's effort in Free Fonn Fabrication (FFF) began in 1987 with the fontation of an internal consortium, Calp)sed of a dozen different activities, whose purpose was to evaluate and apply, where possible, this errerging tecl:mology. Each of the consortium members agreed to contribute sare rroney and, rrore irrportantly, one or rrore people to work on this project. By the following year (1988) the first rrachine, an SLA-1, had been installed at the Alpha Msmufacturing Develq:ment Center and fomed the cornerstone of the FFF Lab.
Homogenization Design and Layered Manufacturing of a Lower Control Arm in Project MAXWELL
(1993) Johanson, Roy; Kikuchi, Noboru; Papalambros, Panos
We briefly describe a new methodology for the design and manufacture of mechanical components and demonstrate the process for the design of an automobile suspension component. The methodology is a unique coupling between advanced technologies for product design and manufacture, which leads to the rapid realization of superior products. The concurrent design and analysis strategy yields information about the optimal structural layout, as well as details about the material composition. The fabrication of such designs requires unconventional manufacturing processes, such as layered manufacturing. Project MAXWELL, therefore, offers the possibility for the integration of layered manufacturing into the mainstream product development and fabrication process.
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.
Laser Sintering Model for Composite Materials
(1993) Nelson, J.C.; Vail, N.K.; Barlow, J.W.
A computer model for the sintering of ceramic/polymer composite materials has been established based on empirical sintering rate data. The model calculates sintering depths which result from variations in the operating parameters which include laser power, beam speed, scan spacing, scan vector length, and initial temperatures of the powder and surroundings. Sintering depths measured in multiple layer parts made of polymer coated ceramic powders are compared to sintering depths calculated by the sintering model.
Machine Vision for Rapid Geometric Modeling
(1993) Koivunen, V.; Bajcsy, R.
Material and Process Parameters that Affect Accuracy in Stereolithography
(1993) Chartoff, Richard P.; Flach, Lawrance; Weissman, Peter
Experimental real time linear shrinkage rate measurements simulating stereolithography are used in an analysis of shrinkage during line drawing in stereolithography. While the amount of shrinkage depends on the polymerization kinetics, shrinkage kinetics and overall degree of cure, it also depends on the length of time to draw a line of plastic. A line drawn slowly will exhibit less apparent shrinkage than one drawn very quickly because much of the shrinkage is compensated for as the line is drawn. The data also indicates that a typical stereolithography resin in the green state may shrink to only 65% of its maximum, thus retaining considerable potential for shrinkage during post-cure. This infonnation can be used to predict the amount of shrinkage to be expected under certain exposure conditions and to fonnulate overall strategies to reduce shrinkage and subsequent warpage that causes shape distortion.
Material Issues in Layered Forming
(1993) Amon, Christina; Beuth, Jack; Kirchner, Helmut; Merz, Robert; Prinz, Fritz; Schmaltz, Kevin; Weiss, Lee
A brief overview of key issues in layered thermal processing is given. Incremental sintering and layered fusion ofpowder and molten droplets are discussed. The criteria for remelting the solid substrate are derivedfrom a one dimensional heat transfer model. Temperature gradients which occur during solidification and subsequent cooling. are responsible for the build up of internal stresses which can be estimated through establishing an elastic beam model. The difficulties as well as opportunities regarding the generation of multi-layer multi-material structures are also described in this article.
Measurement of the Thermal Conductivity of Powders by Two Different Methods
(1993) Sih, Samuel S.; Barlow, Joel W.
The thermal diffusivities and thermal conductivities of powders, especially PMMA-coated silicon carbide, at various temperatures, have been tested by two different dynamic methods, the water-bath method and the laser-heated method. The thermal conductivity data found by these two techniques are found to be consistent with each other.
Optimization of 2D CT Data Sets for Three-Dimensional
(1993) Levy, Richard A.
Computer-generated anatomic modeling using radiologic data is a well-known entity. Currently, state of the art 3D modeling systems lack the variable thresholding, user interactive, capabilities of 3D imaging software.1 We investigated clinical parameters - cr scan plane, 2D filter algorithm, surrounding medium - and tested a simple mathematical thresholding algorithm based upon experimentation with a cr phantom, to evaluate a semiautomated approach to 3D craniofacial imaging and model generation. (Figure 1)

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