Reduction Ratio
The ratio of starting cross-section to finished cross-section — the measure of how much the metal has actually been worked.
Cast structure is coarse and contains porosity along the centreline. Forging closes it, but only in proportion to how much the section is reduced. A 4:1 reduction is the usual minimum for general engineering work and 6:1 is normal for rotating and dynamically loaded parts. Because the ratio depends on the starting billet, it is a purchasing decision as much as a shop floor one — a forging quoted from a nearly-finished-size billet has barely been forged at all.
Related terms
Where this applies
open-die-forgings, forged-shafts
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