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Metal Casting is a manufacturing process in which metal is melted and poured into molds where it solidifies into geometrically complex components. Metal Casting is unique among metal component forming processes for a variety of reasons.

First, the array of available metal casting processes are capable of producing very simple to extremely complex components in almost any metal, ranging in weight from less than an ounce to several hundred tons. In addition, metal casting processes are available that make it economical to produce a single prototype part, while others achieve their economies in creating multiple units. Understanding the metal casting basics can help you design for manufacturability and utilize processes that meet your specific requirements.

The fundamental process of metal casting consists of five basic elements:

• Molding—The mold cavity must be formed from a material that will withstand the operating temperatures and conditions of the chosen casting process and metal.
• Pouring—The molten metal is poured into the mold and travels through its passages to fill the mold cavity.
• Solidification—During the solidification process, the metal cools and becomes a solid shape.
• Mold Removal—The cooled casting is removed from the mold.
• Secondary Operations—The casting is trimmed, cleaned, heat-treated, machined, inspected, painted, etc.

Molding processes can be broken into four general categories: sand casting processes; permanent mold processes; ceramic processes; and rapid prototyping.

Sand Casting Processes: Fundamentally, a mold is produced by shaping a refractory material to form a cavity of a desired shape such that molten metal can be poured into the cavity. The mold cavity needs to retain its shape until the metal has solidified and the casting is removed. This sounds easy to accomplish, but depending on the choice of metal, certain characteristics are demanded of the mold.

Die Cast and Permanent Mold Processes: At least three families of molding and casting processes can be categorized as permanent mold processes. These include die casting (high-pressure diecasting), low-pressure permanent mold casting and permanent mold casting. Unlike sand casting processes, in which a mold is destroyed after pouring to remove the casting, permanent mold casting uses the mold repeatedly.

Ceramic and Plaster Mold Processes: This family of casting processes, Investment Casting, Ceramic Molding, Plaster Molding are unique in that ceramic and plaster are used as molding media. These processes offer a high degree of precision in regard to dimensions, as well as excellent surface finishes.

Rapid Prototyping Processes: Rapid Prototyping (RP) is a general name that encompasses numerous methods used to fabricate objects from CAD data. There are a number of different RP processes, and new developments are constantly being made. RP most commonly is used with investment casting, sand casting and plaster molding to produce an actual cast part to test for form, fit and function, as well as to determine the approximate final properties of the cast parts.