Published: Jan 2005
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FOR MOST APPLICATIONS, EVEN CLOSED DIE forgings will require some machining. Machining of open die forgings is expected to be more extensive, and can involve almost all of the operations to be found in a modern machine shop. Machining, apart from bringing the forging to the required dimensions, also removes surface scale and imperfections as well as the decarburized skin. Depending on the application, some closed die forgings may be acceptable for use simply after scale removal, as for example, by shot blasting. The decarburized surface, however, remains in this case, and will offer reduced fatigue strength. Examples of the use of die-forged components with at least some asforged surfaces include some automotive suspension parts and some piping fittings. Good examples of combined asforged and machined surfaces are the closed die forged or continuous grain flow crankshafts used in automotive, locomotive, marine, and aero applications. In these applications, the areas that see low operating stresses in service-such as the webs-are left in the descaled, as forged condition, while the highly stressed main bearing and crankpin journals are machined to close tolerances and high surface finishes. In this example, variations in section size, and therefore mass in the as forged locations, caused by forging tolerances, are countered by dynamic balancing of the finished crankshaft.