The Tenth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas
in Austin on August 9-11, 1999, was attended by over 170 national and international researchers.
Papers addressed SFF issues in computer software, machine design, materials synthesis and
processing, and integrated manufacturing. New sessions on ceramic materials and multiple
materials SFF were added to this year's program. The diverse domestic and foreign attendees
included industrial users, SFF machine manufacturers, university researchers and representatives
from the government. We are pleased once again with the strong showing of university students.
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
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 new researchers and users entering the field.
The editors would like to extend a warm "Thank You" to Rosalie Foster 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 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 the Office of Naval
Research and the National Science Foundation for supporting this meeting financially. The meeting
was co-organized by the University of Connecticut at Storrs, and the Mechanical Engineering
Department, Laboratory for Freeform Fabrication and the Texas Materials Institute at The
University of Texas at Austin.
This report describes the application of Curved LOM to the direct fabrication of polymer matrix
composites (PMCs). The overall methodology of directly fabricating PMC parts involved the use of the
Curved LOM machine to lay-up and shape "green" composite laminates from prepreg feedstocks,
followed by vacuum bag / oven cure and consolidation. The conventional Curved LOM laminator was
replaced with a vacuum thermoforming apparatus to better accommodate the bonding of commercially
available prepregs. The study also demonstrated that it is possible to interface a general composite design
sofiware package with the Curved LOM machine via the curved slice file (.CSF) format. Taken together,
these two improvements allow for improved flexibility in manufacturing PMC components, from both a
material handling and a design point-of-view. A simple C-shaped panel was fabricated and tested to
demonstrate the overall feasibility of the process for PMCs. A glass fiber 1 epoxy prepreg obtained from a
commercial supplier was used as a model material system. It was found that the cumulative accuracy of
the overall process was good, and the mechanical properties of the laminates were acceptable for nonstructural applications for which the material is normally used.
(1999) Liu, Zhien; Suppakarn, N.; Cawley, James D.
In laminated object manufacturing of ceramic components, lamination is one of the most
important materials issues. Good lamination ensures monolithic component after firing.
Otherwise, lamination defects that inevitably will occur in the parts will affect the
properties of ceramic components. Adhesive (both liquid and non-liquid) lamination
processes were developed for the cut-then-stack (CAM-LEM) procedure. The non-liquid
adhesive lamination is discussed in detail.
In solid freeform fabrication (SFF) processes involving thermal deposition, thermal control
of the process is critical for obtaining consistent deposition conditions and in limiting residual
stress-induced warping of parts. In this research, nondimensionalized plots (termed process maps)
are developedJrom numerical models of laser-based material deposition of thin-walled structures
that.map out the effects of changes in laser power, deposition speed and part preheating on process
parameters. The principal application of this work is to the Laser Engineered Net Shaping (LENS)
process under development at Sandia Laboratories; however, the approach taken is applicable to
any solid freeform fabrication process involving. a moving heat source. Similarly, although thinwalled structures treated in the current work, the same approach could be applied to other
commonly fabricated geometries. A process map for predicting and controlling melt pool size is
presented .and numerically determined results are compared against experimentally measured melt
poollengthsfor stainless steel deposition in the LENS process.
Direct laser metal deposition is a means of near net shape processing that offers a number
of advantages including rapid prototyping and small lot production. With the LENS (Laser
Engineered Net Shape) process [Ref 1], parts are fabricated by creating a laser melted pool into
which particles are injected. Fabrication proceeds by moving the work piece, thereby building
the structure line by line and layer by layer. In this manner a wide variety of geometries and
structures can be fabricated. During fabrication, a complex thermal history is experienced in
different regions of the build. These thermal histories include remelting and numerous lower
temperature thermal cycles. Furthermore, the use of a finely focused laser to form the rapidly
traversing pooL can result in relatively high solidification velocities and cooling rates.
Previous work has developed LENS as an advanced manufacturing tool rather than
exploiting its potentially unique attributes: real time control of microstructure, tailored material
properties at different part locations, the production of graded structures, etc. Very often,
however, material properties are not significantly different than those of wrought materials.
The. goal of this program is to exploit the unusual thermal environment experienced during
fabrication, and the ability to design and vary alloy composition. In this paper we describe this
approach using H13 tool steel in which only the thennal fields are varied through changing
process parameters to achieve desired properties.
An initial study ofthe processing parameters affecting deposition quality ofTi-6AI-4V was conducted using the LENSTM direct laser deposition system. The significant number ofprocess variables
presents a problem in determining relative effects. A few ofthe easily identifiable variables were isolated
and the deposits were characterized qualitatively by comparison oflayer adhesion, porosity, and dimensional accuracy. These characteristics were compared for each deposit while processing variables such as
laser power, travel speed, and hatch spacing were varied. The results led to the development of a
set of optimum processing conditions that produce a quality deposit.
Indirect fused·· deposition process is utilized.·.. to ·fabricate controlled porosity ceramic
structures using alumina, mullite, zirconia, LSCF-perovskite, tricalcium phosphate and
hydroxyapatite, where pore size, pore shape and pore connectivity are varied from one end to
the other end of the parts. Some of these porous ceramics are then infiltrated with metals via
pressureless reactive metal infiltration to form novel metal-ceramic composites. Thispaper will
describe processing, structures of various porous and metal-infiltrated composites and their
physical and mechanical properties.
Fused deposition of ceramics (FDC) is a solid freeform fabrication technique based on
extrusion of a highly loaded thermoplastic binder system. The present FDC process uses filament
feedstock of 1.780 mm ± 0.025 mm diameter. The.filament acts as both the piston driving the
extrusion process as well as the molten feedstockbeing deposited. The filaments need to be able
to provide and sustain the pressure needed to drive the extrusion process. Failure to do this
results in failure via "buckling". The filament compressive modulus determines the ability ofthe
filament to provide·and sustain the required pressure to drive the extrusion. The viscosity ofthe
feedstock material, nozzle geometry and volumetric flow rates employed determine the pressure
needed to drive the extrusion process. In this worktheiextrusion pressure for a particular material
termed PZT ECG9 (52.6 Vol.% PZT powder in ECG9i~inder) was measured experimentally as a
function of volumetric flow rate and nozzle geometry.rhe compressive modulus ofthe material
was determined using a miniature materials tester (Rheoinetrics, Inc., Piscataway, NJ). A process
map has been developed. The map is based .on the quantity MIE, and predicts the performance
of the material in a FDC process as a.functioIl.ofnozzleg~ometry and volumetric flow rate. In
general, it is observed that when MIE exceeds a critical value, called APcr/E, there is an
increased tendency for the filament to buckle. A. preliminary fluid flow model for extrusion of
PZT ECG9 through a FDC nozzle has also been developed using Polyflow™ software. The
model predicts the observed trend in pressure drop with flow rate and nozzle geometry with
(1999) Bharvirkar, Manish; Nguyen, Phong; Pistor, Christoph
The quality of Fused Deposition Modeling parts that are built using the standard parallel
road approach depends significantly on the orientation of the slices. In this study the expansion
coefficient, tensile strength and elastic. modulus of FDM parts made from ABS were determined
experimentally. The parts were built using the standard toolpath (parallel roads) with a uni
directional stacking sequence. The results were used to determine the thermo-mechanical
properties for an.individual slice. Classical lamination theory was applied to predict properties
and stiffness of matrix parts with arbitrarily oriented stacking sequences. The results of these
predictions are compared with experimental results for a quasi-isotropic stacking sequence.
(1999) Rodriguez, J. F.; Thomas, J.P.; Renaud, J. E.
Fused-Deposition (FD) creates parts using robotic extrusion of set.D.i-liquid .polymer
fiber, which molecularly bonds with neighboring fibers via thermal-dlffuslo.n bonding. T~e
strength ofthe. part depends on the bulk polymer strength, themesostructure ~flber layout, vOid
geom~try, extent of fiber bonding), and thefiber-t~-fiber ~ond strength. The ~nfluence of these
factors on the mechanical strength of FD-ABS.plasttc parts IS reported.along with the.FD process
variable settingsfor maximum strength. Substantial increases in transverse strength are achieved
at the optirnal settings and additional increases can be achieved by post..fabrication annealing.
Keywords: Stratasys, fused-deposition, ABSplastic, functional parts, strength, mesostructure, polymer diffusion.