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Investment Castings
The
term "investment" refers to the ceramic materials that are
used to build a hollow shell into which molten metal is poured
to form the castings. The origin of the term investment comes
from the solid mold process where a plaster type material
is poured or "invested" into a container that holds a clustered
tree of small plastic patterns that are identical to the casting
being produced. After the investment material has set, the
disposable patterns are burned out leaving a hollow cavity
into which the metal is poured.
The same holds true for the investment or "lost wax" casting
process. Wax is injected into an aluminum die to produce a
pattern that is an exact replica of the part to be produced.
For every casting, a wax pattern must be manufactured. The
patterns are then clustered around a central sprue and repeatedly
dipped into an agitated vat of ceramic and allowed to dry.
After a shell thickness of approximately 3/8" has been built;
the molds are dewaxed by either flash firing at high heat
(1400 °F)
or autoclaving (pressure and steam). The hollow shells are
then preheated to 800-2000 °F
depending on the alloy to be poured and the molten metal is
cast into the hot shell. After cooling, the ceramic is vibrated
and blasted off the metal parts and discarded. The balance
of the cleaning operations (cut off, grind, heat treat, straightening,
blast) are straight forward and quite similar to the other
casting processes.
Cost Savings
Because investment casting can produce parts
which achieve or closely approximate finished dimensions,
you can enjoy significant savings through elimination of machining
operations, increased tool life and reduction of labor cost
and parts scrap rate.
Investment castings can provide one casting,
which might have previously required several pieces made in
different processes and several different materials.
Cost savings of 50 % or more are common
with castings versus other manufacturing processes.
When dealing with expensive alloys, you don’t want waste
in the form of metal chips, shavings or cut off pieces. With
investment castings “you get what you pour.”
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