The original definition of forging is the "mechanical deformation of metal when heated to a plastic state". However, in recent years it has come to include similar operations done in the cold or room temperature state as well. There are two main types of forgings: open end forging and close end forging.Open die forging involves the shaping of heated metal parts between a top die attached to a ram and a bottom die attached to a hammer anvil or press bed. Metal parts are worked above their recrystallization temperatures-ranging from 1900°f to 2400°f for steel-and gradually shaped into the desired configuration through the skillful hammering or pressing of the work piece. While impression or closed die forging confines the metal in dies, open die forging is distinguished by the fact that the metal is never completely confined or restrained in the dies. Most open die forgings are produced on flat dies. However, round swaging dies, v-dies, mandrels, pins and loose tools are also used depending on the desired part configuration and its size. Although the open die forging process is often associated with larger, simpler-shaped parts such as bars, blanks, rings, hollows or spindles, in fact it can be considered the ultimate option in "custom-designed" metal components. High-strength, long-life parts optimized in terms of both mechanical properties and structural integrity are today produced in sizes that range from a few pounds to hundreds of tons in weight. In addition, advanced forge shops now offer shapes that were never before thought capable of being produced by the open die forging process. Open-die forging is also known as smith forging. In open-die forging a hammer comes down and deforms the workpiece, which is placed on a stationary anvil. Open-die forging gets its name from the fact that the dies (the working surfaces of the forge that contact the workpiece) do not enclose the workpiece, allowing it to flow except where contacted by the dies.
Therefore the operator needs to orient and position the workpiece to get the desired shape. The dies are usually flat in shape, but some have a specially shaped surface for specialized operations. For instance, the die may have a round, concave, or convex surface or be a tool to form holes or be a cut-off tool. Open-die forging lends itself to short runs and is appropriate for art smithing and custom work. Other times open-die forging is used to rough shape ingots to prepare them for further operations. This can also orient the grains to increase strength in the required direction.
