What Surface Finish Does Forging Give?
As-forged surfaces run around Ra 12.5 to 25 µm — visibly rough, carrying scale and following the die's own condition. Anything smoother requires a subsequent operation.
As-forged hot forging surfaces run Ra 12.5–25 µm and carry scale. Shot blasting cleans and evens them without much reducing roughness. Cold forging achieves Ra 0.8–3.2 µm directly, turning reaches Ra 1.6 µm and grinding Ra 0.4 µm or better.
- As-forged (hot)
- Ra 12.5 – 25 µm
- Shot blasted
- Uniform matte, similar Ra
- Cold forged
- Ra 0.8 – 3.2 µm
- Turned
- Ra 1.6 µm typical
- Ground
- Ra 0.4 µm or better
What Surface Finish Does Forging Give? at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Hot forged surfaces run Ra 12.5–25 µm
- Cold forging achieves Ra 0.8–3.2 µm
- Turning reaches Ra 1.6 µm
- Grinding achieves Ra 0.4 µm or better
Finish by Process
Hot forging gives Ra 12.5–25 µm. Shot blasting cleans and evens it without significantly improving roughness. Cold forging achieves Ra 0.8–3.2 µm directly. Machining reaches Ra 1.6 µm turned, and grinding Ra 0.4 µm or better.
- Hot forged: Ra 12.5–25 µm
- Cold forged: Ra 0.8–3.2 µm
- Machined: Ra 1.6 µm
- Ground: Ra 0.4 µm or better
Specifying Finish Sensibly
Specify surface finish only where it functions — sealing faces, bearing seats, sliding surfaces. Applying a fine finish requirement to as-forged surfaces means machining every surface, which is expensive and usually pointless.
People also ask
Why are as-forged surfaces rough?
The surface reproduces the die's own condition plus scale formed during heating, and neither is smooth at the microscopic level.
Should I specify surface finish on as-forged surfaces?
Only where it functions. Requiring a fine finish on as-forged surfaces forces machining of every face, adding cost with no benefit on non-functional surfaces.
Does surface finish affect fatigue life?
Yes, significantly. Fatigue cracks initiate at surface irregularities, which is why highly stressed areas are machined or ground rather than left as forged.
Topics covered on this page
- surface finish
- Ra value
- as-forged
- shot blasting
- grinding
- fatigue initiation
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
What surface finish does hot forging produce?
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Around Ra 12.5 to 25 µm as forged, carrying scale until shot blasted.
Does shot blasting improve surface finish?
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It cleans and makes the surface uniform but does not significantly reduce roughness. Machining or grinding is needed for that.
What finish can you achieve on machined surfaces?
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Ra 1.6 µm turned as standard, and Ra 0.4 µm or better ground.