..... Click the link for more information. 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.
forging
In metallurgy, the process of shaping metal and increasing its strength by hammering or pressing. In most forging an upper die is forced against a heated workpiece positioned on a stationary lower die. To increase the force of the blow, power is sometimes applied to augment gravity. The number of blows struck is carefully gauged by the operator to give maximum effect with minimum wear on the die. Forging presses employ hydraulic or mechanical pressure instead of blows; most can exert only a few hundred tons of pressure, but giant presses, used for forging parts of jet aircraft, are capable of up to 50,000 tons of pressure. See also drop forging.
forging [′fȯrj·iŋ]
Forging
The plastic deformation of metals, usually at elevated temperatures, into desired shapes by compressive forces exerted through a die. Forging processes are usually classified either by the type of equipment used or by the geometry of the end product. The simplest forging operation is upsetting, which is carried out by compressing the metal between two flat parallel platens. From this simple operation, the process can be developed into more complicated geometries with the use of dies. A number of variables are involved in forging; among major ones are properties of the workpiece and die materials, temperature, friction, speed of deformation, die geometry, and dimensions of the workpiece.
In practice, forgeability is related to the material's strength, ductility, and friction. In terms of factors such as ductility, strength, temperature, friction, and quality of forging, various engineering materials can be listed as follows in order of decreasing forgeability: aluminum alloys, magnesium alloys, copper alloys, carbon and low-alloy steels, stainless steels, titanium alloys, iron-base superalloys, cobalt-base superalloys, columbium alloys, tantalum alloys, molybdenum alloys, nickel-base superalloys, tungsten alloys, and beryllium. See Metal
Some of the terminology in forging is shown in the illustration. Draft angles facilitate the removal of the forging from the die cavity. The purpose of the saddle or land in the flash gap is to offer resistance to the lateral flow of the material so that die filling is encouraged. Die filling increases as the ratio of land width to thickness increases up to about 5; larger ratios do not increase filling substantially and are undesirable due to increased forging loads and excessive die wear. The purpose of the gutter is to store excess metal. The flash is removed either by cold or hot trimming or by machining.
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A number of methods produce the necessary force and die movement for forging. Two basic categories are open-die and closed-die forging. Drop hammers supply the energy through the impact of a failing weight to which the upper die is attached. Another type of forging equipment is the mechanical press. For large forgings the hydraulic press is the only equipment with sufficient force. However, the speed for such presses is about one-hundredth that of hammers. See Metal forming
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