lostfoam

Lost foam, or lost-foam casting, is a metal casting process that uses patterns made from expanded polystyrene (EPS) foam to form the mold cavity. The foam pattern is shaped to the final part and may include integrated features such as gating and risers. The pattern is then surrounded by a sand mold, typically unbonded silica sand, or incorporated into a ceramic shell or slurry coating to improve surface finish and heat resistance. Molten metal is poured into the mold; the heat vaporizes or melts the EPS pattern, which is displaced by the metal, and the surrounding mold captures the shape of the part. The result is a near-net shape casting with little or no pattern tooling required for complex geometries, reducing setup time and tooling costs, especially for low-to-mid volume production.

Advantages of the process include the ability to produce complex geometries without traditional pattern making, reduced lead times, and lower tooling costs. It is well suited for aluminum, magnesium, and zinc parts, and is used for automotive components, housings, manifolds, and prototypes. The method can produce good dimensional accuracy and surface finish when properly coated and vented, though process control is crucial to manage gas evolution and shrinkage.

Limitations and challenges include potential surface roughness or defects caused by EPS decomposition gases, porosity if venting is inadequate, and the need for careful control of coatings and binders. Dimensional tolerances may require post-casting machining for some parts. Environmental and safety considerations arise from burning EPS and the associated emissions during casting.

See also: investment casting, sand casting, foam pattern casting.