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Forging

Complicated sections that cannot be rolled or sections of which only a small quantity is required are usually forged. Forging is an important hot-forming process. It is used in producing components of all shapes and sizes from quite small items to large units weighing several tons. The metal, preheated to the appropriate forging temperature, is shaped mainly by upsetting (compressive deformation) between impact surfaces or pressure surfaces, that is, by hammering or pressing the heated metal until the desired shape is obtained.

Hammering can be used only on relatively small pieces. Because hammering transmits its force almost instantly, its effect is limited to a small depth. Therefore, it is necessary to use a very heavy hammer or to subject the part to repeated blows to ensure complete working of the section. If the force applied is too weak to reach the center, the finished forged surface will be convex or bulged. The advantage of hammering is that the operator has control over both the amount of pressure applied and the finishing temperature, and he is able to produce parts of the highest grade. This kind of forging, also called smith forging, is used extensively where only a small number of parts are needed. Considerable machining and material are saved when a part is smith-forged to approximately the finished shape.

Pressing is used when the parts to be forged are large and heavy or where high-grade steel is required. Because a press is slow acting, its force is uniformly transmitted to the center of the section. This gives the interior and exterior grain of the metal the best possible structure throughout.

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