Lost Foam CASTING PROCESS:

The Lost Foam casting process is a relatively new method of producing castings developed around 1960. The process is primarily used for aluminum, gray iron, and ductile iron castings, although it is envisioned that the process will be used by other segments of the casting industry as the technology matures.

Lost Foam casting uses patterns made from polystyrene (the same material that is used in foam coffee cups) or polymethylmethacrylate (PMMA), placed in un-bonded sand. The use of foam patterns can help improve both the casting process and the final cast product by eliminating the need for cores and improving the accuracy of the casting. Cores can be eliminated because un-bonded sand fills internal spaces of the foam pattern, forming the cavity in the casting.

By eliminating cores, foam patterns can be used to cast complex internal geometries, including multiple passages and curved walls of variable thickness. Unlike most other casting methods, the pattern does not need to be withdrawn from the mold prior to casting. The foam pattern must be coated to obtain a high-quality casting. The patterns are made from expandable polystyrene or PMMA beads, which evaporate from the heat of the molten metal during pouring.

The use of low-density, pre-expanded beads minimizes the amount of vapors to be vented. A single pattern may be made of several sections or multiple patterns may be combined into a cluster and glued together to allow complex or multiple castings per mold. Once the pattern is made, it is coated with a permeable ceramic or other refractory wash by dipping, spraying, or pouring. As with other casting methods, gating and risering systems are included, but in Lost Foam casting, the gating and risering systems are glued to the pattern. The assembly is suspended in a flask with side vents, and un-bonded sand is poured around the pattern while the flask is being vibrated, which allows the sand to pack tightly around the pattern.

During melting and pouring operations, the vapors from the polystyrene escape through the coating, into the mold, and out of the flask. The coating and the rigidity of the sand allow the mold to stay in place. After the casting has solidified, it is transferred to the shakeout area and proceeds through cleaning and finishing operations like other casting processes. The shakeout process is easy with un-bonded sand.