Lost-foam casting (LFC) is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax.
This process takes advantage of the low boiling point of polymer foams to simplify the investment casting process by removing the need to melt the wax out of the mold.
Commonly cast metals include cast irons, aluminium alloys, steels, and nickel alloys; less frequently stainless steels and copper alloys are also cast.
The size range is from 0.5 kg to several tons. The minimum wall thickness is 2.5 mm and there is no upper limit.
Typical surface finishes are from 2.5 to 25 µm RMS. Typical linear tolerances are ±0.127 mm/mm.
This casting process is advantageous for very complex castings that would regularly require cores.
It is also dimensionally accurate, maintains an excellent surface finish, requires no draft, and has no parting lines so no flash is formed.
The un-bonded sand of lost foam casting can be much simpler to maintain than green sand and resin bonded sand systems.
Lost foam is generally more economical than investment casting because it involves fewer steps.
Risers are not usually required due to the nature of the process;
because the molten metal vaporizes the foam the first metal into the mold cools more quickly than the rest, which results in natural directional solidification.
Foam is easy to manipulate, carve and glue, due to its unique properties.
The flexibility of LFC often allows for consolidating the parts into one integral component; other forming processes would require the production of one or more parts to be assembled.
The two main disadvantages are that pattern costs can be high for low volume applications and the patterns are easily damaged or distorted due to their low strength.
If a mould is used to create the patterns there is a large initial cost.