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
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
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.
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.
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.
(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.
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
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.
(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.
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
(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.
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] .
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
(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.
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.
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.