The processes described in this chapter produce what are known as the wrought metals. These are important engineering materials because of their strength and toughness. Common metalworking processes included in this chapter are metal rolling, cold drawing, pipe and tube manufacture, forging, and extrusion. Hot working is done above the re-crystallization temperature. Cold-worked metal is formed to shape by the application of pressure at temperatures below the critical point and, for the most part, nominally at room temperature. Warm working, or warm forming as it is often called, is performed at some intermediate temperature above room temperature, but below the re-crystallization temperature of a metal. When metal is rolled, it passes and is squeezed between two revolving rolls. Bars of all shapes, rods, sheets, and strips of all common metals are commonly finished by cold rolling. Foil is made of the softer metals in this way. Round, rectangular, square, hexagonal and other shapes of bars up to about 102 mm (4 in.) across or in diameter, wire of all sizes, and tubes are commonly finished by cold drawing. Pipe and tubing is formed by butt-welding, lap-welding, or seamless tube forming. Forging may be done in open or closed dies. Open die forgings are nominally struck between two flat surfaces, but in practice the dies are sometimes vee-shaped, half-round, or half-oval. Closed die forgings are formed in die cavities. When metal is extruded, it is compressed above its elastic limit in a chamber and forced to flow through and take on the shape of an opening.
Product ID: BK00PUB8_E_CH-11