The forging of metals
We have seen that metal components can be produced cheaply and efficiently by the casting process. Cast components however are usually brittle, and break easily. Some metal components like crankshafts, connecting rods, spanners, etc, have to stand up to conditions of severe stress when in use. Components produced by the forging process, are much stronger than those produced by casting or by machining from solid bar material. The reason for this lies in the fact that the grain structure is different. Each metal grain is a minute crystal, and the strength of a metal component depends on the orientation of the grains. Fig 9.1 shows the difference in grain structure between a gear tooth that has been machined on the right of the diagram, and a gear tooth that has been forged, on the left.
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