forging, shaping metal by heating it and then hammering or rolling it. Forging is the method by which metal was first worked when it came into use about 4000 BC in Egypt and Asia. Modern forging is done with a power-driven hammer; Dies are usually used. These are steel blocks hollowed out or carved in relief in the shape of the desired part. One die is stationary, the other is attached to the underside of a hammer or press ram. A piece of metal is then hammered or squeezed until it takes on the shape of the die cavity. Sometimes there are several sets of dies that form the metal in stages into the final shape. Smaller parts may be forged cold; larger parts, hot. Maximum pressure exerted is about 100 tons per square inch. Variations of the forging process are called sizing, heading, and coining. Some industrial machines for forging are the drop hammer, steam hammer, and hydraulic press. Forging toughens iron and steel, while casting makes them brittle.
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