Investment Castings
"Lost Wax"
(overview)
With the advancements in rapid prototyping,
investment casting has become the leading technology
for producing high-quality castings quickly
and inexpensively. Investment casting, also
known as the "lost wax" process, consists
of attaching an expendable pattern (usually
wax, and for our purposes generated via rapid
prototyping) to a tree which acts as its sprue,
then repeatedly dipping the pattern into a stucco
light slurry. The ceramic shell is allowed to
dry before the next layer of slurry is applied.
The end result is a thick ceramic shell surrounding
the pattern and its sprue. The next step is
to melt or to flash out the remaining pattern.
Once the pattern is removed, the hollow ceramic
shell is now filled with molten metal. After
an appropriate cooling time - usually quite
short - the ceramic shell is broken off, and
the metal casting is processed as usual. A major
advantage to investment casting is that either
ferrous of nonferrous materials can be used.
The recent big breakthroughs relate to how rapid
prototyping is used in the process: the wax
materials for use with the Actua RP machine,
SLA QuickCast patterns and longer-life epoxy
tools from SLA patterns for production wax patterns.
Waxes from ThermoJet
The ThermoJet is the ideal wax prototyping machine.
Using an .STL file, the part to be cast can
be programmed for the current shrink and orientation.
The envelope size of the ThermoJet is 10"
x8" in the X and Y axis and 8" in
the Z axis. Bigger parts can be made in multiple
pieces and then glued together.
SLA QuickCast Patterns
The SLA QuickCast process is a build style that
leaves a hollowed out honeycombed structure
as the pattern. This hollowed pattern allows
the resin to flash out at temperatures about
1600°F (870°C), without expanding and
cracking the ceramic shell. This requires special
handling, but the results and benefits can be
great.
SLS CastForm Materials
SLS patterns built using CastForm material are
infiltrated with foundry wax to create an ideal
investment casting pattern. They ideal for parts
requiring higher tolerance, multiple-run parts
and larger parts.
Epoxy Wax Injection
Many times when multiple metal prototypes are
needed, the expendable patterns can become quite
expensive. A more practical approach may be
to make wax injection molds from rapid tooling.
This procedure usually reduces the cost and
can still give multiple metal castings in three
to four weeks.
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The term | Simple
