Lost Foam Costing is a sub type of Investment
Casting. This type of casting method uses foam pattern as the
investment. This method benefits from the advantages of the foam
properties helpful to make simple and cheap castings. These types of
simple castings are impossible using the regular cope and drag method.
Casting process:
Foam Shaping: The original foam pattern of the Polystyrene is generally molded or carved.
Carving
Polystyrene: The formed foam or polystyrene is then carved using
traditional carving tools or the new-age hot-wire cutting tools. It can
also be sanded easily.
Injecting Polystyrene in a Mold:
Polystyrene contains pentane as a blowing agent and is commonly used
for beads. The beads are pre-extended, stabilized and then blown into
the mold to form pattern sections. A steam cycle forces the beads to
expand fully, after this the fuse together and then it undergoes an
in-mold cooling cycle. The final shape if very complex, then it is
molded in sections. A cluster is formed by aging and gluing together
the shaped foam sections.
Preparing Final Mold (Investment) for
Casting: Gates and Raisers are generally attached to the pattern, they
are also the part of the casting as this helps reduce the shrinkage.
Pouring, dipping or spraying are the different methods used for coating
the foam cluster with ceramic investment. The reason for this coating
is that it forms a barrier and helps to prevent the molten metal to
penetrate or cause sand erosion while pouring. Structural integrity of
the casting is protected thanks to the coating. The cluster when dried
is backed up with un-bonded sand and is placed in a flask. Proper and
uniform compaction is then achieved by performing mold compaction using
a vibrating table. After all this process and after proper compaction,
the mold is ready to be poured.
Automatic pouring is the
preferred method in Lost Foam Casting. This is the most critical
process and also a bit difficult than the traditional foundry practice.
As there are no parting lines or fins to remove the cleaning is easier
and requires far more less time and operations in the Lost Foam Casting
process.
Advantages of Lost Foam Casting: Due to its unique
properties, foam is easy to carve glue and manipulate. It also provides
accurate dimensions as Lost Foam Casting is more accurate and effective
than sand casting. There are no fins or parting lines the finishing
process is easy and less time consuming. The elimination of cores makes
complex casting designs easy. Lost Foam Casting also allows us to
control the wall thickness and thus no core prints are required thus
eliminating shifts or fins and also saves the trouble of sand mixing
and core defects. As there are no drafts multiple levels of casting is
possible. Precise gate and riser replacements are achieved.
Unconventional forms of casting that are difficult or impossible to
achieve in traditional cope and drag method are easily achieved in Lost
Foam Costing. Due to simpler process and easy finishing work, the
process is very cost effective and lowers the overall price of the
final product.
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