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
Selective Laser Sintering of Bioceramic Materials for Implants
(1993) Lee, Goonhee; Barlow, J.W.
Selective Laser Sintering (SLS) process is employed for fabrication of biocerarnics for orthopedic implants. Hydroxyapatite and Calcium Phosphate ceramics are coated with polymer as a intermediate binder by using a spray drier. Polymer coated materials are SLS processed to make green parts, which are infiltrated and fired to remove the polymer. SLS processed green parts of hydroxyapatite have low density due to the small particle size with large specific surface area. This paper discusses the possibilities and problems in free-form fabrication of bioceramic.
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.
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.
Selective Laser Sintering of A1203-
(1993) Subramanian, Kam
Synthesis, Selective Laser Sintering and Infiltration of High Super Tc Dual Phase Ag-YBa2Cu307-x Superconductor Composites
(1993) Agarwala, Mukesh K.; Bourell, David L.; Manthiram, Arumugam; Birmingham, Britton R.; Marcus, Harris L.
Fine, homogeneous dual phase Ag-YBa2Cu307-x composite powders were prepared by a simple colloidal sol-gel co-precipitation technique. Silver did not react with or degrade YBa2Cu307-x. Bulk porous samples of pure YBa2Cu307-x and Ag-YBa2Cu307-x were made from powders by Selective Laser Sintering. The porous parts were further densified by infiltrating silver into pores, resulting in a dense, structurally sound dual phase superconducting composite. Laser processing parameters were varied to obtain optimum microstructure. The laser sintered parts required oxygen annealing after infiltration to restore the orthorhombic, superconducting structure. X-ray diffraction and Tc measurements indicate some impurity phases present in samples processed under aggressive laser conditions.
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.
Selective Area Laser Deposition of Silicon Carbide
(1993) Tompkins, James V.
Supersolidus Liquid Phase Selective Laser Sintering of Prealloyed Bronze Powder
(1993) Gopalakrishna, B.; Bourell, David L.
Solid Freeform Fabrication of Silicon Carbide Shapes by Selective Laser Reaction Sintering (SLRS)
(1993) Birmingham, B.R.; Marcus, H.L.
This paper describes an investigation ofthe production ofsilicon carbide shapes by Selective Laser Reaction Sintering (SLRS). One type ofSLRS process, which combines laser sintering of silicon with acetylene decomposition, is briefly outlined, and the mechanisms important to the process are discussed. A series oftest shapes are made at different acetylene pressures to determine pressure effects on conversion to silicon carbide. X-ray diffraction spectroscopy is used for bulk analysis ofthe shapes, and Auger electron spectroscopy is used for surface analysis. The results indicate that acetylene pressure does have a strong effect on silicon conversion to silicon carbide, and SLRS can be used successfully to make silicon carbide shapes.
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.
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.
Strategy for Composite Development in Rapid Prototyping
(1993) Charan, B.; Bagchi, A.; Ogale, A.A.; Renault, T.
The polymeric parts built with a stereolithography apparatus (SIA) have good dimensional accuracy, but they cannot be used as functional prototypes because of their low mechanical properties. This paper describes the concept of fabricating fiber composites by 3-D photolithography. In this process, the strength and stiffness of parts are improved over stereolithography by adding fiber reinforcement to the resin. An automated desktop photolithography unit (ADPU) was designed and built in-house, to add continuous E-glass or quartzfibers in situ to the photoresin. Thefirst composite parts made by 3-Dphotolithography are presentedin this paper, thefeasibility ofcurvilinearaddition offibers is demonstrated, andstrategies for selective reinforcement are discussed.
Machine Vision for Rapid Geometric Modeling
(1993) Koivunen, V.; Bajcsy, R.
Potential Application of Solid Free-Form Fabrication (SFF) Process in Ceracon P/M Forging
(1993) Raman, R.V.; Rele, S.V.; Anderson, R.L.
The Ceracon Process is a patented[ll, low cost powder metallurgy process for achieving near-net-shape, full density parts. It. isasimple.·consolidation.technique which utilizes conventionalpowder metallurgyequipmenfand set-up. The Cetacon Process is a quasi-isostatic,hot consolidation technique, that utilizes a ceramic particulate material as a pressure transmitting medium instead ofagasmedia as is used in. hipping. Pressures up to 200 K.si can be used and a broad range ofmetallic, ceramic, and polymeric materials and composites have been successfully processed£2-6] .
Thermal Analysis and Modeling of Steady-State Rod Growth During Gas-Phase Solid Freeform Fabrication
(1993) Maxwell, James L.; Pegna, Joseph
An analysis ofthe steady-state growth ofrods during gas-phase solidfreeform fabrication is presented. It is demonstrated that heat transfer controls the evolution ofshape during laser-induced pyrolysis of slender 3-D structures. Insulating and conductive deposit materials were studied, using both simple analytic and numerical simulations to demonstrate how steady-state rod growth is achieved.
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.
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.
Powder Layer Position Accuracy in Powder-Based Rapid Prototyping
(1993) John Lee, Sang-Joon; Sachs, Emanuel; Cima, Michael
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.

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