Lost-foam casting (LFC) is a casting method used to create solid
metal parts from molten metal. When a part is created through
casting, a mold is used to produce the desired shape. In lost-foam
casting, the mold is made from polystyrene foam, which is lost
during the casting process as the liquid metal melts it and replaces
its shape; hence the name “lost-foam.” Although lost-foam casting is
often used to make machine parts, decorative and other objects can
be produced using the same method. The tools used by casters range
from homemade devices to industrial-grade equipment.
The first step of lost-foam casting is the creation of the foam
mold. A block of polystyrene foam is cut
into the exact shape of the finished product using hand or power
tools. For applications where the dimensions of the finished piece
must be exact, power tooling is preferred for a more consistent
shaping of the foam. The mold is then dipped in sheetrock mud or
plaster and coated thoroughly.
After the foam mold is finished, it is buried in a container; for
example, a metal drum; filled with compacted sand. The very ends of
the foam shape are left exposed to facilitate the entry of the
molten metal into the mold. A homemade tool can be used during this
step to help the process along further. This tool, which consists of
a hinged cylinder that can be opened and closed along the side by
long handles, is placed on the sand so that it surrounds the foam
piece. When the metal is poured, the cylinder walls contain it and
allow it to build up over the piece, creating more pressure and,
therefore, a more thorough casting.
Aluminum is often used in lost-foam casting, especially by
hobbyists, but it is possible to use any metal as long as it is hot
enough to evaporate the foam mold. In most cases, the molten metal
must be at a temperature of 1000° F (about 538° C) or
higher. Furnaces capable of melting metal at these high temperatures
can be purchased commercially or made from everyday materials such
as clay or brick. The metal is melted inside a special container
known as a crucible, which is made from a material with a high
melting point, such as graphite. Once the metal is melted, the
crucible is gripped using tongs or fixed bars and tipped to pour the
liquid metal onto the mold.
As the molten metal dissolves the foam, it flows into the empty area
and assumes its shape inside the sand. Ideally, a perfect replica of
the foam piece is created in this way. The piece is allowed to cool
for a few minutes, and is then removed from the sand for further
cooling in a bucket of water. After sand and debris are brushed from
the piece, it can be polished or machined further as needed.
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