First, a pattern ( like Lost Foam Investment Casting Car Union) is created out of polystyrene foam. This type of foam is essential in this casting method. It has a good thermal insulator and chemical resistance, allowing it to work normally at temperatures below 75 °C.
The foam pattern can be created in a variety of ways, depending on the difficulty and details of the product.
Creating a pattern for the lost foam process
The foam pattern is partially made and glued together for highly detailed casting patterns. For small volumes, foundries frequently hand-cut or machine patterns from a solid foam block. A hot wire foam cutter can be used if the pattern is simple enough.
If the volume is large enough, the pattern can be mass-produced using a method similar to injection molding.
Polystyrene beads are injected under low pressure into a pre-heated aluminum mold. Following that, steam is applied, causing the polystyrene to expand even more to fill the empty cavity and form the pattern or section. The final pattern contains 97.5% air and 2.5% polystyrene.