Technology Information

Metal Casting

Lost Foam Metal Casting 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.

Here are the details of the Casting Process:

Foam Shaping: The original foam pattern of the Polystyrene is generally molded or carved.

Carving Polystyrene: You will want to used some older carving tools that you see around various shops or maybe a new age hot wire cutting tool in order to cut the formed foam. 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 Metal 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. Finally, after a lot of detailed work and proper compaction you can now pour into the mold.

Automatic pouring is the preferred method in Lost Foam Metal 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. Lost Foam casting becomes very helpful when you are trying to cast something that is very difficult with cope or drag mehtods as it will be much easier with Lost Foam Casting.  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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Metal Casting

Lost Wax Metal Casting is known as Cire Perdue in French. This is a very important process where a scuplture made by an artist is used to cast bronze. The Lost Wax Casting method is also known as  Investment Casting in the modern industrial world. A long time ago in ancient times, this method was used to cast small bronze sculptures but as it has evolved today, it is used to make a lot of different things and each foundry uses the process differently. Today this developed method of Lost Wax Casting is used to make articles like fine jewelery, show pieces, dental restoration, a few specific industrial parts and also some machine tools.

Process of Lost Wax Metal Casting :
 
Rough Sculptor making: A creative artist makes an original sculptor or mold or an artwork by using raw material like wax, plaster of Paris or clay. A mixture of oil based clay and wax is preferred as these materials retain their softness.

Final Mold Making: A mold is then made as per the original sculptor. The mold is made up of two pieces and a key with shim is placed between the two pieces during construction so the mold can be put accurately back together. Molds are generally made using plaster or fiberglass or any other material that may be suitable. An inner mold of latex or vinyl or silicone is put pup preserve the details of the original art work. Generally, the original art work made of plaster mold cracks and breaks during the initial phase of deconstruction. Many a times, numerable molds are required to get the exact replica of the original art work.

Filling up the mold: Once the latex and plaster mold is complete and finished, molten wax is poured into the mold till it gets an even coating all around the mold. The thickness of the wax coating is around 1/8 inch. This process is then repeated until the desired thickness is achieved.

Removal of wax replica: The hollow wax replica of the original art work is then removed from the mold. The original mold can be used for making more wax replicas, but due to the wear and tear of the original mold the reuse of the mold is limited.

Softening: Each wax mold is then chased or softened using heated metal tools. The metal tools are rubbed around portions that show cracks or the joining line of the mold, where the pieces have come together. Separately molded wax pieces are then heated and attached. You will then do what is called “dress” the mold so you can hide any and all imprefections. The final piece then looks like a bronze sculpture.

Making paths for molten bronze: It is also known as “spuring”, in short the wax copy is then branched with treelike wax, so that the molten bronze reaches the right parts and also it helps the air to escape. The critical and careful spuring begins from the top of the wax copy. The top of the copy is attached to by wax cylinders to different points on the wax copy.

Slurry, burnout, testing, pouring, release, metal-chasing, and painting are the final steps in the process of Lost Wax Metal Casting .

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