This Proceedings of the Second Solid Freeform Fabrication Symposium that was
held at The University of Texas in Austin on August 12-14, 1991 demonstrates the very
active interest in this fully integrated approach to design, materials processing and
manufacturing. The active participation of speakers and attendees from industry,
universities and government give a clear indication of the importance that SFF in its many
variants has in the future of manufacturing. As SFF extends itself into structurally sound
parts made of polymers, metals, ceramics and their composites the number of people and
institutions involved will continue to grow exponentially. The organizers look forward to
this growth and the continued availability of the Solid Freeform Fabrication Symposium to
serve as a source of technical exchange among the researchers involved in the area.
The Symposium was organized in a manner to allow the multi-disciplinary nature of
the SFF research to be presented coherently. The initial session described the computer
interfacing required for SPF. This was followed by a session associated with polymer
research on SFF. A session on modeling SFF was then presented. Two sessions were
offered describing the latest techniques and modifications of SFF. Sessions on the
application of SFF to ceramics and metals were then presented. The final session
concentrated on the gas phase approach to SFF and to a general discussion on SFF and
where it was going. The written versions of the presented papers were incorporated into
The editors would like to thank the speakers for there prompt delivery of the manuscripts that allows the timely publication of these Proceedings. The state of the SFF art as represented by these Proceedings will serve both the people presently involved
in this research area as well as the new researchers coming into Solid Freeform Fabrication.
The editors would also like to extend a warm thank you to Nancy DeLine 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 and the
attendees for their contributions. We look forward to a continued close cooperation in
organizing the Symposium.
Organizing committee: Fritz Prinz,
Peter R. Sferro,
Robert L. Brown,
Selective area laser deposition (SALD) has been used to deposit carbon from
acetylene. Working at the relatively high pressures required to produce high deposition
rates can result in explosive uncontrollable growth. Pr~vious computational modeling
indicates that the energy released from the exothermic decomposition of acetylene to
carbon may be responsible for this behaviour[l]. Since methane decomposes
endothermically to form carbon over certain temperatures, it is possible that methane
addition to the process may help control the deposition rate. The purpose of this paper
is to describe SALD experiments that were performed using various partial pressures of
acetylene and methane as precursor in order to determine if combining an endothermic
and an exothermic reaction effects the control of the SALD process.
The overall selective area laser deposition process was modeled using the two-layer, three
dimensional solid phase heat transfer with the moving boundary condition considered, gas phase
mass transfer, and film growth coupled equations. A modified front-tracking finite difference
method was used to solve the moving boundary heat conduction in thick deposits. The results
correlate with the experimental observations.
Concerns critical to selective area laser deposition are discussed. Variables affecting
deposition rate, dimensional control, and surface uniformity are analyzed. Localized growth
results in undesirable morphology, and contributing factors are cited. Catalytic powders increase
nucleation rate and provide superior temperature profiles resulting in good surface uniformity.
Specific process control devices are investigated.
A model system has been employed to investigate .the use of selective laser sintering (SLS) with
a post-processing step to produce a compound having different properties than the precursor
powders. The powder mixture examined consisted of95% (59% Ni and 41%8n) plus 5% ZnC12.
This weight fraction of nickel and. tin produces. the intermetallic compound Ni3Sn upon equilibrium
annealing. ZnCl2 was used as a wetting agent. Parts were fabricated using SLS and were then
post-process annealed to create the intermetallic. Metallographic techniques and x-ray powder
diffraction were used.to characterize the parts before and after annealing.
The Selective Laser Sintering process was used to manufacture green copper parts from a
copper-polymer mixture. PMMA was used as the polymer binder for the metal. The green
part was fired in a furnace under reducing conditions to obtain a pure metal part. The
metal-polymer system and the conditions used to make parts are described in this paper.
The effect of laser parameters and particle sizes on part density are also discussed.
Keywords: laser sintering, copper, polymer, part density, dwell time, shrinkage.
Solid Freeform Fabrication (SFF) as an overall approach in the
manufacturing field has been applied to very different areas and on
different materials systems including polymers, ceramics, metals and
vapor phase. Even though it is clear that polymers have enjoyed a rapid
and successful advance in terms of applications, research in the other
areas have shown potential applications as well.
In this paper, Cu-Sn/Pb solder and Cu-Sn blends have been used as
starting material for the Selective Laser Sintering (SLS) manufacture of
SFF objects. The general properties of the objects thus produced are
presented. In particular, density and microstructural characterizations
results are discussed..
Techniques for controlling the microstructure of sprayed steel structures are
discussed in this paper. Steel is arc sprayed onto shaped substrates to form tooling. The
quality of the tool is greatly influenced by the microstructure of the material and the interlamella
regions of the deposit. This work is focused on characterizing the microstructure,
improving the state of the inter-lamella regions, and discusses our success in forming
pseudo-alloys and graded shells by mixing sprayed materials. Microstructure control has
interesting implications for other research as well, such as the MASK & DEPOSITS approach
of forming objects.
The feasibility of processing ceramic powders by Selective Laser Sintering has been
reported in an earlier paperl . Material systems we have investigated include alumina based
systems with ammonium phosphate or boron oxide as low temperature binders which are
the systems discussed in this paper. With bOth systems, a secondary heat treat.rJ1ent is
necessary to realize the high temperatute properties of the materials. This paper will focus
mainly on the mechanical properties of the composite bodies. In particular, the influence of
particle size, powder mix composition, laser parameters and secondary heat treat.rJ1ent on
density, strength and dimensional stability of the final product will be discussed.
It has been proposed that a thin polymer layer applied to the
surfaces of finely divided ceramic powders would serve as a suitable
intermediate binder for Selective Layer Sintering of ceramic pans. In this
study, the effects of completeness and fraction of coa nd particle size
distribution on sintering rates and strengths of coated ridized glass are
examined. The effect of the coating as a binder during Selective Layer
Sintering as well as the binder's burnout capability during post processing
steps are also investigated.
(1991) Weiss, Lee E.; Prinz, Fritz B.; Siewiork, Daniel P.
This paper present.s t.he framework for a solid-freeform-fabrication syst.em based on thermal spray
shape deposition t.o build mult.i-mat.erial st.ruct.ures by incremen tal build-up of t.hin cross-sect.ional layers.
The basis of theMD* System (recursively, Mask and Deposit.) is to spray each layer using disposable
masks to shape each layer. A thermal spray approach has the potential to build dense parts with
desirable mechanical properties. Metal. ceramic, plastic, laminate, and composite structures can be
deposited. Since l11asking enables selective deposition wit.hin a layer, complet.e assemblies composed of
different mat.erials can be creat.ed in a single process. For example, int.egrated electronic/mechanical
structures are feasible.
Solid freeform fabrication technologies offer exciting possibilities for improving
product quality by direct manufacture of products. .One example of such product
improvement is the fabrication of artificial limb sockets by selective laser sintering (SLS).
Currently these sockets are produced at the University of Texas Health Science Center at
San Antonio by digitizing the residual limb with a 3D laser scanner, modifying this
geometry appropriately using a proprietary CAD system, producing a mold with a
computer-controlled milling machine, and vacuum forming the final product. This paper
describes a new manufacturing technique whereby the digital socket data from the CAD
system provide input to a SLS workstation to produce the final socket directly, without the
intermediate step of fabricating a mold pattern. The advantages of this process include
integration of the prosthesis attachment fitting and socket as one component and greater
control of local socket geometry for superior stress relief characteristics.
It has been almost four years since the SLA - 1 ushered in the
new technology of StereoLithography, and about 2\ years since 3D
Systems introduced the SLA-250. Since then, nearly 300 systems
have been installed worldwide and are currently providing benefits
in a range of applications which might well be summarized by the
term "Rapid Prototyping and Manufacturing" or "RPM".
During the past year the accuracy of parts built with
stereoLithography has benefitted significantly from nine important
technological advances. The research and development efforts which
formed the foundation for this progress originated within the
Process, Chemistry and Software departments of 3D Systems.
The following is a listing, and brief description, of the key
features of each of these advances.
With accelerating growth and competition in today's global marketplace, manufacturers
face the daunting tasks of meeting changing market needs, maintaining market share, and
reasserting a technological edge. Now, more than ever, adopting new technologies is a key
component in ensuring the successful outcome of new projects--and in producing longterm
With Laminated Object Manufacturing (LQM) process, three dimensional objects
are manufactured by sequentially laminating and cUtting two-dimensional cross-sections.
The.rnediumused.inLOMprocess isaQhesive-coatedsheet• materials.. As seen in Figure 1,
the sheetmateria.l carries the adhesive either on one sideQr both sides, or it cQntains the
adhesive ill itself, like woven composite material impregnated with bonding agent. The
adhesive,which can be pre-coatedonto>material or be deposited prior to bonding, enables
layers of sheet material to be attached to each other so as to construct a three-dimensional