Metal forming involves the reshaping of metals while still in the solid state. By taking advantage of the plasticity of certain metals, the forming process makes it possible to move a metal solid from into current shape into the desired form. Further, it accomplishes this without melting, thereby avoiding any potential difficulties in the handling of molten metal or in the integrity of molded products.
Generally, metal forming operations can be categorized as hot, cold or warm working processes. The temperatures involved in these processes are not static, but vary from metal to metal; in some cases, room temperature may mean hot-working conditions. Hot working involves deforming a metal under conditions above its recrystallization temperature, usually at temperatures higher than 60% of its melting point (Kelvin). For most metals, cold working is typically performed at room temperature or slightly higher temperatures; as long as the temperature of the operation is below the metal’s recrystallization temperature, it qualifies as cold working. Warm working is performed at intermediate temperatures between those of recrystallization and cold-working.
Hot working processes include rolling, forging and extrusion. Rolling is also performed as a cold working process, and involves sending metal stock through a set of rollers. The rollers deform the original stock and output it in the preset shape. Sheets, strips, rails and other similar shapes can be produced by rolling. Forging uses presses, hammers and other compressing devices to shape metal stock, and can also be performed cold. Parts made by the cold forging process are often referred to as cold-headed parts. Extrusion is a process whereby stock is forced through a die and emerges as a tube with a nearly identical cross section.
In addition to cold rolling and forging, cold working processes include shearing , drawing and bending. Bending involves the reshaping of metal around a linear axis, while shearing is a chip-free cutting process. Blanking and piercing are both forms of shearing that consist of cutting shapes out of the metal work piece. Drawing resembles extrusion, except that the work piece is pulled, not pushed through the die—it is also performed as a hot working process.
Metal forming is used to create all manner of products, including tubes, pipes, metal sheets, fasteners, wire and much more. Many of the metal objects we encounter in everyday life, from thumbtacks to file drawers, were likely produced by one or more metal forming operations.
