Lost foam casting is a method of creating metal parts using an expanded polystyrene mold that is lost during the casting process. The foam mold is covered in drywall mud or plaster, buried in compacted sand, and filled with molten metal. The metal dissolves the foam and takes its shape within the sand. The finished piece is left to cool and can be polished or further processed as needed.
Lost foam casting (LFC) is a casting method used to create solid metal parts from molten metal. When a part is created by casting, a mold is used to produce the desired shape. In lost foam casting, the mold is made of expanded polystyrene, which is lost during the casting process as 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 items can be produced by the same method. The tools used by the wheels range from homemade devices to industrial-grade equipment.
The first stage of lost foam casting is the creation of the foam mold. A block of expanded polystyrene is cut into the exact shape of the finished product using hand or power tools. For applications where the dimensions of the finished part must be exact, power tooling is preferred for more consistent foam shaping. The mold is then dipped in drywall mud or plaster and carefully covered.
After the foam mold is finished, it is buried in a container, such as a metal drum, filled with compacted sand. The very ends of the foam form are left uncovered to facilitate entry of the molten metal into the mold. A homemade tool can be used during this step to further aid the process. This tool, which consists of a hinged cylinder that can be opened and closed laterally by long handles, is placed on the sand so that it wraps around the foam piece. As metal is poured, the walls of the flask contain it and allow it to build up on the workpiece, creating greater pressure and, therefore, a more accurate casting.
Aluminum is often used in lost foam casting, especially by hobbyists, but any metal can be used 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 of a material with a high melting point, such as graphite. Once the metal is melted, the crucible is gripped by tongs or fixed bars and tipped over to pour the liquid metal onto the mould.
As the molten metal dissolves the foam, it flows into the empty area and takes its shape within the sand. Ideally, this creates a perfect replica of the foam piece. The workpiece is left to cool for a few minutes, then it is removed from the sand for further cooling in a bucket of water. After the sand and debris have been removed from the piece, it can be polished or further processed as needed.
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