Hammer Forging (Flat Die): Preferred method for individual forgings. The shaping of a metal, or other material, by an instantaneous application of pressure to a relatively small area. A hammer or ram, delivering intermittent blows to the section to be forged, applies this pressure. The hammer is dropped from its maximum height, usually raised by steam or air pressure. Hammer forging can produce a wide variety of shapes and sizes and, if sufficiently reduced, can create a high degree of grain refinement at the same time. The disadvantage to this process is that finish machining is often required, as close dimensional tolerances cannot be obtained.