Composite Stereolithography Materials: The Developer's Perspective
It is widely acknowledged that the speed and
efficiency of product development at many companies has benefited from
the use of stereolithography (SL) to produce functional, structural and
aethetic models. Significant advancements in materials robustness,
aesthetics and processing efficiencies have been achieved which, in
turn, have expanded the use of stereolithography as a rapid prototyping
process.
The recent introduction of composite SL
materials and their proven commercial applicability has paved a new
path toward expanded performance capabilities and enhanced versatility
of the SL process. In particular, increasing attention is being given
to composite materials' potential in rapid tooling and rapid
manufacturing applications.Striking a Balance
Historically, the range of properties that can be achieved by SL
materials has been limited to formulations of UV-curable resins,
typically based on epoxy and acrylate chemistry. While the physical
performance of engineering thermoplastic materials remains the industry
benchmark, achieving such results with crosslinked, thermosetting SL
resins is a difficult task. Development of SL products that optimally
balance heat resistance, stiffness and toughness, and impact strength
in a single material has proven elusive with neat, liquid formulation
building blocks.
Meanwhile, the utility of fillers and reinforcements are well known in commercial engineering plastic applications.
The introduction of composite additives has been evaluated and
discussed over a number of years dating back to the early 1990s, when
DuPont presented information on a material targeted for investment
casting that would include hollow spheres.
The first commercial composite SL material for rapid prototyping,
however, was not widely available until 2002 when DSM Somos (New
Castle, DE) introduced ProtoTool 20L, a highly filled SL material.
The technical challenges in producing an SL material with composite
properties for use in current SL equipment are many, including the
difficulty of adding a material that will not interfere with the
light-sensitivity of the photopolymers.
There is also the challenge of finding fillers that can be suspended
adequately in the liquid matrix to minimize settling during the
stereolithography process. While reinforcement properties are
influenced by particle size and aspect ratio, SL process accuracy
imposes limitations relative to surface quality of the imaged object.
Finally, there are potential health and safety issues to consider when
dealing with fillers, relative to post-processing oper-ations such as
sanding.NanoForm's Opportunities
The recent introduction of DSM Somos NanoForm, which contains amorphous
nano-particles, is one example of how these composite-related technical
challenges can be met successfully.
NanoForm's advantages over traditional SL materials include excellent
thermal properties (a heat deflection temperature over 500ºF at 66 psi
with thermal post-cure), low moisture absorption (0.3 percent), and
very high strength and stiffness.
New market opportunities for composite materials include expansion of
SL into traditional SLS applications, which require high stiffness and
heat deflection as well as high dimensional consistency.
One major opportunity for growth of stereolithography parts made from composite materials is in wind-tunnel applications.
Carl Dekker, President of Met-L-Flo Inc. (Geneva, Illinois), reports
that a major aerospace company is already using NanoForm parts for wind
tunnel testing. These parts were tested at speeds of Mach 0.6 to 0.95
for approximately 54 hours with no sign of degradation. Although
aluminum is the current standard material for their final configuration
high-speed aero testing models, there is clearly growth potential for
composite SL parts.
NASA has also considered using NanoForm for wind tunnel testing
applications, but at much higher temperatures of approximately 600 to
900ºF for short periods of time, normally less than 10 seconds.
The major issue NASA has encountered with traditional unreinforced SL
materials is the degree of water absorption. Dimensional accuracy is
essential and, since their models are scaled to obtain results,
traditional SL parts can grow significantly out of proportion while
waiting to be tested. The presence of non-absorbing fillers in NanoForm
limits water absorption and related material expansion.
Composite SL materials are dramatically increasing the application
potential for stereolithography and, in particular, rapid tooling
applications, due to their high heat resistance and improved stiffness.
Real benefits of using these materials are continuously being
discovered as innovative people learn to exploit their improved
performance properties.
For more information please contact Ty Bacon, sales and marketing manager, DSM Somos (New Castle, DE) at (302) 326-8100.
