Aluminum casting involves pouring a liquid metal into a mold that contains a cavity of a detailed shape, and then is allowed to solidify. The solidified part is known as a casting, which is ejected or broken out of the mold to complete the casting process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other techniques. In the aluminum casting process molding materials used can be sand or metal. The pouring methods used are gravity, vacuum, or low pressure.