Lost foam casting is relatively a new casting technique that has the characteristics of both investment casting and sand casting. It is similar to evaporative pattern casting, with the pattern made up of foam instead of wax. The foam pattern is coated with refractory material, as in investment casting;
However, the shell is then surrounded by compacted un-bonded sand to provide enough strength to sustain. The foam patterns vaporize when molten metal is poured into the shell. Castings from this process exhibit the quality and accuracy of investment casting with the lower costs and greater flexibility of sand casting.
A foam pattern is made using expanded Polystyrene. This can be formed by closed-die molding, machining, or assembly from multiple parts. Risers and gates are included at this stage.
Multiple finished patterns are glued together to form a cluster.
The cluster is coated with permeable refractory slurry, usually by dipping. When dry, the refractory coating forms a hard shell around the foam pattern. Various refractory coatings can be used depending on the surface finish required.
The lost foam mold is placed in a foundry flask or box and surrounded by loose, un-bonded sand which is then vibrated to compact.
Molten metal is poured into the mold. The foam pattern instantly vaporizes, and metal fills the void left within the refractory shell.
Once cooling and solidification have taken place, the sand and shell are broken away, risers and gates are removed, and the finished foam cast piece remains.
The cast product or component can then be finished, treated, or machined as with any other casting.
Lost foam casting is a delicate process. Foam Patterns made from foam can easily be damaged or distorted, therefore all foam patterns and molds must be handled with care. In the pouring stage, the molten metal must reach temperatures of above 1000°F in order to fully ‘dissolve’ the foam pattern and produce a complete cast piece.
We make sure only the right amount of molten metal is poured into the mold, and the casting is thoroughly cooled in a controlled environment before the mold can be broken.
This method shares many of the advantages with lost wax investment casting, but involves fewer steps and uses cheaper materials, thus it is generally more economical than the latter. Foam patterns are also easier to shape (can be glued and carved), which further aids the freedom of design.
All these features help keep waste levels down and lower per-unit production costs. This process is ideal for high-quality single casting, small volume production, prototyping, or supersized castings (from 0.5 kg up to 10 tons).
It is a process most useful in producing complicated casting assemblies for automotive parts like cylinder heads, weldments, etc. Cast iron, aluminum alloys, steels, nickel, and in some cases stainless steel and copper alloys are cast in this process.
Omnidex has been working with some of the best lost foam foundries to produce exceptional products over the years. We are very familiar with the challenges in this type of casting, and we take extreme care at every step to ensure the best result. Our engineers have extensive experience in designing lost foam casting patterns, which can be made with CNC machining or foam injection for higher precision.
We have an arsenal of technology, including computer simulations, specialized foam materials, and automated machines which we can deploy as the situation dictates.
Contact our Customer Service and let us know how we can help to catapult your next project to success.
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