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Lost foam casting is a type of evaporative pattern casting. This method is quite similar to investment casting which uses wax instead of foam in the pattern making process.

The foam pattern was first used in metalworking in 1958. Although this mold casting technique is not as popular as other methods such as sand mold casting or permanent casting, it maintains outstanding advantages, especially in casting complicated and precise molds.

Unlike traditional methods which include the pattern withdrawn process before casting and require skillfulness in the pattern removal step, with respect to the lost foam method, the pattern is evaporated when the molten metal is poured into helping to reduce these considerations.
The lost foam casting process

Lost foam process
The lost foam casting technology included 5 steps: designing the pattern; applying insulation painting; placing the pattern into the sand flask; pouring the molten metal; and collecting the castings.
How a lost foam pattern is made?
Firstly, a pattern is designed from polystyrene foam. This type of foam plays an important role in this casting method. It is a good thermal insulator and chemical resistance, enable working normally at the temperature below 75 ℃.
Depending on difficulty and details of the product, the foam pattern can be made from different manners.
Making the pattern for lost foam process
For highly detailed casting patterns, the foam pattern is partly made and glued together. For the small volume, foundries often make patterns by hand-cut or machined from a solid foam block. If the pattern is simple enough, a hot wire foam cutter can be applied.
In case the volume is large, the pattern can be mass-produced by a process similar to injection molding.
Polystyrene beads are injected in a pre-heated aluminum mold at low pressure. After that steam is applied leading to polystyrene expands more to fill the empty cavity and then form the pattern or a section. The final pattern is approximately 97.5% air and 2.5% polystyrene.
Casting process
Once the pattern is formed, it is coated with insulation paint, placed in a flask and surrounded in un-bonded sand and compacted.
the pattern is coated with insulation paint in lost foam process
The covering paint works to increase the durability of the mold surface, protect from erosion, and broken. Whereas, the flask is designed suitably for this method so that when the molten metal is poured into the mold, the gas generated by foam burning is withdrawn completely.
After molten metal is poured into the foam pattern, the foam pattern is burned out and the casting is formed.
Lost foam method is applied to cast steel product
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