Typically the term investment casting  involves the loss of the master and
the
mold, as in "lost wax" casting The wax is burned out (vaporized) in the
invstment
plaster. The molten metal is poured, centrifuged, steam pushed, etc into the
plaster
and then the plaster is broken from the part. Properly accomplished this
provides
incredible detail in the finshed part. A version of this is often used for
the
super alloys for turbine blades and such. The lost styrofoam is usually done
in
sand, and the molten aluminum vaporizes the foam as it is poured in. On some
engine blocks you can even see the "foam cooler type balls " as a texture on
the cast surface. - Vance

The Saturn block is created in just this way.  You can see the styrofoam
 pattern on the outside of the block.  Looks kinda funny
to see that pattern on an engine block.  Tom Webber

 
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