Rapid prototyping is a
technology which has developed in the last decade. Through the use of
modern solid modeling CAD packages, combined with laser systems and new materials, we can now generate solid parts
directly from the computer model without human interaction. In addition, these
parts are generated in a matter of hours, and are accurate to a few
thousandths of an inch. Compare this to handmade prototypes which can take weeks or
months to create and tend to contain errors.
At MSC Technologies, we utilize the following processes:
Stereolithography is a method that employs
an ultraviolet laser to cure a thin layer of liquid plastic into a solid. The process operates by
taking a thin layer of the light-sensitive liquid plastic and passing
the laser beam over the points where the part is solid. Once a pass is
completed, another layer of the liquid is added to the existing part, and the process repeats until
the full part height is achieved. SLA parts are extremely accurate, and tend to
have excellent surface finishes. A variety of SLA materials are
available for different purposes, including waxes, plastics, and flexible
elastomers. Most SLA materials do tend to be somewhat brittle, which means they break
easily, as we have proven on many occasions.
OBJECT MANUFACTURING - LOM
Laminate object manufacturing builds a
part by taking individual sheets of paper that have a layer of glue on one side, and building up successive
sections of a part. LOM is very useful for larger parts, as the
process builds these much faster than the other processes. LOM is not as effective
for very small parts as the flexural stiffness of the paper is usually too
low for small parts. LOM parts are accurate, and very easy to sand and paint.
LOM parts, if untreated will tend to absorb humidity and can crack
because of it. LOM parts also have different strengths in different
directions due to
the paper layers.
DEPOSITION MODELING - FDM
Fused deposition modeling is a process
that most closely resembles a miniature glue gun. In fused
deposition modeling, a heat softening and curing plastic is melted in a small nozzle which puts down a very fine
bead wherever the solid part is supposed to be. FDM parts have a rougher
surface finish than an SLA part, but typically are stronger and more
This is a two stage process: First,
a master prototype is made by one of the above processes. This master is
then used to make a silicone rubber mold. Once the molds are made,
liquid urethane rubber is placed inside the mold and allowed to cure. Once cured, you have a urethane copy of your master
The process allows the creation of a larger number of prototypes (up to
about a dozen, possibly more) rapidly and accurately. Additionally,
urethane castings are typically more durable than any of the master
prototypes, and can be made faster and for a much lower cost.
When a single metal part is needed,
and it is too complex to fabricate by hand, we can turn to CNC milling. CNC stands for Computer Numerical
Control. In this process, the computer controls the motions of a milling
machine, guiding it in the fashion of the old saying "cut away
everything that doesn't look like the part." While the theory is simple, the actual
application is more complex.
The process yields a single part, but this part can, theoretically, be
made out of anything, and if correctly made, can perform in an identical
fashion as the real part. CNC parts, however, tend to take longer than the other
processes, and are usually more expensive. CNC parts become more cost
effective as they grow larger, and if a wider variety of materials can
be used (aluminum parts typically cost less than steel).
If very complex steel parts are
needed, or many steel parts are needed, in- vestment casting may be the
technique of choice. Investment casting begins with a wax pattern piece, which can be made by the
stereolithography process. This pattern is coated with a very fine plaster-like
material called investment. Layers of
this investment are built up until a thick layer is formed.
The wax is then melted out in an oven, leaving behind a cavity in the
investment that is a perfect copy of the master part. This cavity can
then be filled with any molten material, brass, aluminum, steel, stainless steel, even
exotic alloys such as inconel. Once the material cools, the investment
is broken away and a finished part is left.
Investment casting can be used to make an unlimited number of parts, all
of which are very accurate to the design. Investment cast parts need
little to no finishing work in most applications before use. However,
investment cast parts are typically more expensive than other processes, and are limited
to parts that are normally no more than 12" in any direction.