Forging Tolerances: What to Expect
Designers frequently specify machining tolerances on as-forged dimensions, which cannot be met by any forging process anywhere. Understanding what forging genuinely holds — and where to add machining instead — prevents expensive arguments later.
- Closed Die (hot)
- IS 3469 / DIN 7526 class E–F
- Cold Forging
- ±0.1 mm
- Warm Forging
- ±0.2 mm
- Open Die
- ±2 – ±5 mm
- Machined Features
- ±0.02 mm
- Machining Allowance
- 1–3 mm closed, 4–15 mm open
Forging Tolerances: What to Expect at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Closed Die (hot): IS 3469 / DIN 7526 class E–F
- Cold Forging: ±0.1 mm
- Warm Forging: ±0.2 mm
- Open Die: ±2 – ±5 mm
- Machined Features: ±0.02 mm
- Machining Allowance: 1–3 mm closed, 4–15 mm open
Where Forging Variation Comes From
Four sources: thermal shrinkage as the part cools, die wear over the production run, die mismatch between top and bottom halves, and flash thickness variation. Each is controlled, none is eliminated.
- Thermal shrinkage on cooling
- Progressive die wear
- Top-bottom die mismatch
- Flash thickness variation
Realistic Tolerance Classes
Closed die forging holds IS 3469 or DIN 7526 class E to F — roughly ±0.5 to ±1.5 mm depending on size. Cold forging holds ±0.1 mm. Open die is looser still, at ±2 to ±5 mm on large sections.
Where to Put Machining
Specify tight tolerances only on machined features and let as-forged surfaces carry the forging class. Machining allowance of 1–3 mm on closed die parts and 4–15 mm on open die parts gives the machinist the stock needed without wasting material.
Topics covered on this page
- forging tolerance standards
- IS 3469 forging tolerance
- DIN 7526 forging tolerances
- as forged dimensional tolerance
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
What tolerance can hot forging hold?
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Class E to F of IS 3469 or DIN 7526 — roughly ±0.5 to ±1.5 mm depending on the dimension and part size.
Why can't as-forged surfaces be tighter?
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Thermal shrinkage, die wear and mismatch all add variation. Tight tolerances belong on machined features.
How much machining allowance should I specify?
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1–3 mm on closed die forgings, 4–15 mm on open die, depending on size and heat treatment route.
Will you review my drawing for forgeability?
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Yes, free of charge with an enquiry. We flag tolerances that cannot be forged and suggest where to machine instead.