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metal casting[′med·əl ¦kast·iŋ]
A metal-forming process whereby molten metal is poured into a cavity or mold and, when cooled, solidifies and takes on the characteristic shape of the mold. Casting offers several advantages over other methods of metal forming: it is adaptable to intricate shapes, to extremely large pieces, and to mass production; it can provide parts with uniform physical and mechanical properties throughout; and depending on the particular material being cast, the design of the part, and the quantity being produced, it can be more economical.
The two broad categories of metal-casting processes are ingot casting and casting to shape. Ingot castings are produced by pouring molten metal into a permanent or reusable mold. Following solidification, the ingots (bars, slabs, or billets) are processed mechanically into many new shapes. Casting to shape involves pouring molten metal into molds in which the cavity provides the final useful shape, followed by heat treatment and machining or welding, depending upon the specific application.
While design factors are important for producing sound castings with proper dimensions, factors such as the pouring temperature, alloy content, mode of solidification, gas evolution, and segregation of alloying elements control the final structure of the casting and therefore its mechanical and physical properties. Typically, pouring temperatures are selected within 100–300°F (60–170°C) of an alloy's melting point. Exceedingly high pouring temperatures can result in excessive mold metal reactions, producing numerous casting defects.
Almost all metals and alloys used by engineering specialists have at some point been in the molten state and cast. Metallurgists have in general lumped these materials into ferrous and nonferrous categories. Ferrous alloys, cast irons and steels, constitute the largest tonnage of cast metals. Aluminum-, copper-, zinc-, titanium-, cobalt-, and nickel-base alloys are also cast into many forms, but in much smaller quantity than cast iron and steel. Selection of a given material for a certain application will depend upon the physical and chemical properties desired, as well as cost, appearance, and other special requirements. See Metal, mechanical properties of, Metal forming