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.
Browsing 1997 International Solid Freeform Fabrication Symposium by Issue Date
During the building of a part using SLS, it is common practice to adjust the temperature
parameters. It is important to control these parameters because ifthey are too high then part
breakout is difficult. Ifthey are too low then parts have poor material properties. One method of
controlling these parameters is by observation through the process chamber window. Any
adjustment can be determined by examining the colour ofthe cross-section in process. By using a
machine vision system to determine colour variation, it is possible to calculate temperature or
laser power adjustments necessary to maintain consistent part quality.
High accuracy is being sought in the rapid manufacturing of long life metal
dies and molds by transferring from layer laminated models. Powder casting serves
as a promising rapid tooling method as it enables high density filling and thus
controls dimensional shrinkage to a considerable extent during sintering and
infutrating This study aims to study the relation between the tooling conditions
and dimensional changes of powder casting and fmd the conditions at which
dimensional changes are minimum. In the experiments performed, a golf ball
model was chosen as an exampIe of a small mold and results show that dimensional
changes can be controlled to below 0.1%, which will facilitate practical application.
By subjecting the cast powder to vibrations after adding the binder to achieve
higher density, and adding fme copper powder to a mixture of two different size
stainless steel powders for dimensional adjustments, almost zero shrinkage control
in rapid tool making was realized.
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.
(1997) Jepson, L.; Beaman, J. J.; Bourell, D. L.; Wood, K. L.
A developing SLS process, known as Multiple Material Selective Laser Sintering,
will allow the material composition of a component to be varied in a controlled
manner. This process could allow the fabrication of functionally gradient materials
(FGMs) in which a blended interface exists. Two potential applications of FGMs are
the reduction of thermal stresses in metal/ceramic joints and the matching of
material properties to functional requirements. A tungsten carbide/cobalt system has
been examined in which the ceramic/metal ratio has been varied in an attempt to
control the hardness/fracture resistance _ratio. An FGM powder bed was manually
fabricated using a discrete banding technique. Results of traditional SLS processing
of this powder bed are presented.
The Fused Deposition of Ceramics (FDC) is based on the commercially available
Fused Deposition Modeling (IDMTM) technique developed by Stratasys Inc. The FDC
process is being currently developed to make complex ceramic parts in an automated
fashion. Although the current focus is on making SisN4 parts, this technique has been
successfully used to make electroceramic (such as PZT) and metallic (such as stainless
As feedstock for the IDC process, filaments loaded with 55 vol% GS-44 Si3N4 is
being used. For the filament to be used in the IDC process, it must possess a unique
combination of physical, rheological and mechanical properties. In this paper, we
investigate the role played by some of the process variables on these properties. Our current
processing sequence to make filaments is as follows - coating of powders with a surfactant,
compounding the ceramic and binder, extrusion into filaments and finally treatment of
filaments to achieve requisite properties. The study has resulted in improvements to the
quality of the filament which can be used for automated FDC. The effect of moisture,
agglomerates and filament aging on FDC will be discussed.
(1997) Elkins, Kurt; Nordby, Howard; Janak, Christopher; Gray IV, Robert W.; Helge Bohn, Jan; Baird, Donald G.
This paper describes an ongoing effort towards extending the capabilities of the fused deposition
modeling (FDM) process to soft thermoplastic elastomers (STPEs). Two thermoplastic
elastomers with hardness of 72 and 78 Shore A, respectively, have been processed into 0.070"
(1.78 mm) filament stock for use in the FDM 1600 rapid prototyping system. The FDM 1600
liquifier subsystem has been modified to accommodate the reduced column strength ofthe STPE
filament stock. Sample STPE parts have been fabricated with ABS material support structures.
(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.