Shrinkage Allowance
Get shrinkage allowance wrong and every single piece is systematically out of tolerance in the same direction — a die problem, not a process one, and it needs the die recut.
Shrinkage allowance is the amount by which a die cavity is cut oversize to compensate for the forging contracting as it cools from forging temperature. For steel it is roughly 1.2–1.5%.
- Steel allowance
- ≈1.2 – 1.5%
- Depends on
- Material and finish temperature
- Applied to
- Die cavity dimensions
- Error signature
- Uniform, systematic offset
Shrinkage Allowance at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Steel allowance: ≈1.2 – 1.5%
- Depends on: Material and finish temperature
- Applied to: Die cavity dimensions
- Error signature: Uniform, systematic offset
Why It Varies
Different materials contract by different amounts, and finish forging temperature affects the total contraction. Stainless steels shrink more than carbon steels; aluminium behaves differently again. The allowance is calculated per material and per part.
Systematic Error Signature
If every piece in a batch is uniformly undersize or oversize by a consistent proportion, shrinkage allowance is the likely cause. Random scatter points to process variation instead — a useful diagnostic distinction.
Topics covered on this page
- shrinkage allowance forging
- forging die shrinkage
- thermal contraction forging
- die oversize allowance
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
What is shrinkage allowance?
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The percentage by which a forging die cavity is cut oversize so the part measures correctly after cooling and contracting.
What is the typical value for steel?
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Roughly 1.2–1.5%, varying with grade and finish forging temperature.
How do I know if shrinkage allowance is wrong?
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Every piece is off in the same direction by a consistent proportion, rather than scattering randomly.