In general terms, metal casting is the process in which a molten metallic substance is poured into a mold to cast specific parts. The framework may be made of ceramic, sand, or metallic components and is often a complex geometric shape. The most common substances used to cast parts are aluminum, magnesium, iron, zinc, copper, and steel.
There are two main types of designs: open and closed. An open mold is a cup like apparatus that is in the shape of the desired part. The liquid is poured into the container and then left open to the environment during the cooling process, as there is no "top" to the structure. While it is one of the two main types of designs, it is seldom used for manufacturing quality parts.
The other type of design is known as the closed mold. This design has a delivery system, allowing you to pour the liquid into the structure. The liquid is not exposed to the elements during the cooling process. These frameworks are used in part manufacturing.
There is one other design that is used in only special cases. It is known as the core. Some parts require an internal geometric pattern and that is what this is used for. Like a traditional construction, the core is an inverse replica of the part needed. During the metal casting process, the core remains within the structure and may be supported by chaplets to prevent moving or shifting.
When you make a metal casting structure, you can either choose to make a permanent or expendable frame. These are just as they sound, and each has their benefits.
A permanent construction can be used to manufacture any part. Typically, these are constructed from a metallic component or ceramic. These are designed to be opened and closed so that you can easily remove the parts. Because they are reusable, they can save money. These do have a downside, as you will be limited on the designs you make because they have to be opened and closed.
Expendable options give you a chance to make more intricate geometric shapes to cast. These forms are made of sand, plaster, or a similar material. However, these can only be used once because you have to destroy them to get the part out. This can become expensive over time.