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Numerous RP technologies are appropriate for use as investment casting patterns. These material displacement casting methods
are among the first industrial processes ever developed and are thousands of years old. The castings produced can be exquisitely
detailed and intricate. Beeswax was the first material used for patterns, but the process is so adaptable that bees themselves
have been used as patterns to produce stunningly detailed gold jewelry. More environmentally and socially conscious jewelry is a
significant application of rapid prototyping-generated casting patterns even today. There are numerous applications in industry
where parts are produced in a variety of metals with castings weighing up to several hundred pounds.
These processes typically involve thickly coating, or investing, a pattern which is made of a material that melts or burns out
easily with a material such as ceramic, which doesn't. The pattern may be extended to provide a gate into which metal in a hot,
liquid state is poured. Passageways are also provided to allow melted or burned pattern material and air to escape. The invested
pattern is then fired in a furnace to burn out or melt the pattern and fuse the ceramic into a strong hollow mold. Molten metal is
then poured into the ceramic mold. After the metal cools and hardens, the mold is broken away to reveal the final object. Extra
gate material is cut off and usually the part will require substantial finish machining and clean-up.
RP-generated patterns can be obtained from fused deposition modeling (FDM) in wax, selective laser sintering (SLS) in polystyrene
or other plastics, and inkjet technology in wax-like plastics. These materials may be melted or burned out of the investment very
cleanly. The patterns from these processes tend to be small to medium in size, and especially for inkjets, offer the highest
resolution and detail.
Stereolithography is also used to produce patterns for investment casting, but the photopolymer materials used in that process are
more difficult to burn out than the materials used in others mentioned above, and also have a tendency to expand and crack the mold.
To get around these problems, 3D Systems has produced a special build style for this application, with the trade name QuickCastTM.
The RP-generated pattern is built in hollow, thin sections which tend to crumple during burn out rather than expand and also
results in a smaller mass of pattern material to remove. The process has been developed over a number of years in partnership with
large foundry companies and customers.
Laminated object manufacturing (LOM) has also been used for investment casting, although a more typical application is for sand
casting. See below. The paper material used in the LOM process is said to sometimes be difficult to remove completely from the
mold, although this is probably a strong function of the particular geometry being produced.
Soligen is a licensee of MIT's 3D Printing process and uses it to produce investments directly without patterns at all. Binder is
deposited to bond a bed of ceramic powder in layerwise cross sections to sequentially build up the investment. Extra powder is
brushed and vacuumed from the green part which is fired to consolidate it in a process similar to a conventional burn out. Soligen
is vertically integrated to produce the final parts in its own foundry.
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