Lost Foam Costing is a sub type of Investment Casting. This type of casting method uses foam pattern as the investment. This method benefits from the advantages of the foam properties helpful to make simple and cheap castings. These types of simple castings are impossible using the regular cope and drag method.
Casting process:
Foam Shaping: The original foam pattern of the Polystyrene is generally molded or carved.
Carving Polystyrene: The formed foam or polystyrene is then carved using traditional carving tools or the new age hot wire cutting tools. It can also be sanded easily.
Injecting Polystyrene in a Mold: Polystyrene contains pentane as a blowing agent and is commonly used for beads. The beads are pre extended, stabilized and then blown into the mold to form pattern sections. A steam cycle forces the beads to expand fully, after this the fuse together and then it undergoes an in mold cooling cycle. The final shape if very complex, then it is molded in sections. A cluster is formed by aging and gluing together the shaped foam sections.
Preparing Final Mold (Investment) for Casting: Gates and Raisers are generally attached to the pattern, they are also the part of the casting as this helps reduce the shrinkage. Pouring, dipping or spraying are the different methods used for coating the foam cluster with ceramic investment. The reason for this coating is that it forms a barrier and helps to prevent the molten metal to penetrate or cause sand erosion while pouring. Structural integrity of the casting is protected thanks to the coating. The cluster when dried is backed up with un bonded sand and is placed in a flask. Proper and uniform compaction is then achieved by performing mold compaction using a vibrating table. After all this process and after proper compaction, the mold is ready to be poured.
Automatic pouring is the preferred method in Lost Foam Casting. This is the most critical process and also a bit difficult than the traditional foundry practice. As there are no parting lines or fins to remove the cleaning is easier and requires far more less time and operations in the Lost Foam Casting process.
Advantages of Lost Foam Casting: Due to its unique properties, foam is easy to carve glue and manipulate. It also provides accurate dimensions as Lost Foam Casting is more accurate and effective than sand casting. There are no fins or parting lines the finishing process is easy and less time consuming. The elimination of cores makes complex casting designs easy. Lost Foam Casting also allows us to control the wall thickness and thus no core prints are required thus eliminating shifts or fins and also saves the trouble of sand mixing and core defects. As there are no drafts multiple levels of casting is possible. Precise gate and riser replacements are achieved. Unconventional forms of casting that are difficult or impossible to achieve in traditional cope and drag method are easily achieved in Lost Foam Costing. Due to simpler process and easy finishing work, the process is very cost effective and lowers the overall price of the final product.
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