1. A foam pattern (see images above) is made using expanded Polystyrene (2.5% Polystyrene, 97.5% air). This can be formed by closed-die moulding, machining or assembly from multiple parts. Risers and gates are included at this stage.
2. Multiple finished patterns (including gating system) are glued together to form a cluster.
3. The cluster is coated with a permeable refractory slurry, usually by dipping. Once dry, the refractory coating forms a hard shell around the foam pattern. Various refractory coatings can be used depending on the surface finish required.
4. The cluster is then placed in a foundry flask or box and surrounded by loose, un-bonded sand which is then vibrated to aid compaction.
5. Molten metal is then poured into the mould. The foam pattern instantly vaporises and metal fills the void left within the refractory shell.
6. Once cooling and solidification has taken place, the sand and shell are broken away, the risers and gates are removed and the finished casting remains.
7. The cast product or component can then be finished, treated or machined as with any other casting.