Q: Is there a specific formula to calculate reduction on rings and sleeves (rings drawn out on a pin)? I understand the way to calculate reduction on rings is to divide the wall thickness of the disc when it is punched by the wall thickness of the finished ring (for example, wall thickness is 10 in. when punched, and 4 in. when finished): The reduction is 2.5-to-1. Is this correct? Is there an additional factor if this ring is drawn out on a pin to gain length?
A: The wall-reduction levels in terms of percent reduction from start to finish is fairly straightforward: In that regard, you are basically correct.
However, total reductions are another matter. You have the pot die (used for most hollow blanks for rings). Assuming you are starting with a cast ingot/billet, the reduction is a function of the backward extrusion reduction followed by the subsequent reduction you described. However, the most important reductions are those obtained in final forging, because that is what controls the grain size of most steels.
The grain size reduces upon annealing if the final forging temperatures are proper for the alloy. For example, overheating can occur at only 2,200°F for a low-alloy steel if there is little or no reduction. For austenitic stainless, final grain size is controlled almost entirely by the final forging reduction.
The reduction requirements for cast material are important to consider, because any remaining cast structures in the resulting billet can compromise the properties and leave residual porosity. However, when starting with press-forged billets (ahead of your ring forging), the reductions should have been sufficient by the method you described.
For more than 40 years H. James Henning held key technical positions in the forging industry, including as director of technology for the Forging Industry Association, and as president of Henning Education Services, a Columbus, OH, firm specializing in customized education and training in forging technologies.
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