The short answer
Use ISO 9001 when the part's critical geometry matches that process naturally. Use AS9100 / NADCAP context when it reduces setups and holds the important features with less risk. The cheapest route is usually the one that keeps the part closest to its natural geometry, not the one with the lowest hourly rate. Buyers should choose based on datum structure, feature access, and secondary operations.
Which geometry favors each process
ISO 9001 is the better fit when the part is driven by you need a general quality management system baseline for many industrial parts. AS9100 / NADCAP context is the better fit when the part is driven by you need aerospace-specific quality discipline or accredited control of special processes. Buyers get cleaner quotes when they classify the part by its functional features, not by the first operation that comes to mind.
A simple rule helps. If the critical dimensions revolve around one axis, start with AS9100 / NADCAP context. If the critical dimensions live across faces, pockets, patterns, or contours, start with ISO 9001. Mixed parts need a more honest conversation about combined processes, secondary operations, or whether one setup must control both feature families.
What moves cost and lead time
ISO 9001 is the general QMS foundation. AS9100 adds aerospace-specific requirements on top of that foundation. NADCAP is different again: it is not a general company-wide QMS but an accreditation model for critical special processes and related scopes. Buyers confuse these all the time.
This is why similar-looking parts can price very differently. Two suppliers may both be able to make the part. One may be able to make it in the natural process route. The other may be forcing the geometry through workarounds. That shows up in cycle time, tool life, fixture count, and inspection effort.
Tolerance and quality implications
The right question is not which certificate sounds impressive. It is which one your part and customer actually require.
Good sourcing teams separate true function from inherited drawing habits. If the tolerance callout is really about concentricity, runout, flatness, or hole position, the process choice should support that directly. Otherwise you end up paying for extra handling just to chase geometry that the wrong machine created in the first place.
The decision error that costs money
A shop with ISO 9001 can be excellent for industrial equipment. An aerospace special process without the right NADCAP scope may still be the wrong choice for flight hardware.
Related reading: CMM inspection explained: what procurement teams need to know and How to write an inspection plan for machined parts.
Comparison table where relevant
| Focus | ISO 9001 | AS9100 / NADCAP |
|---|---|---|
| What it signals | General QMS discipline | Aerospace-specific discipline or accredited special process |
| Use case | Broad industrial sourcing | Aerospace and defense programs |
| Scope style | Company QMS | QMS or process-scope accreditation |
| Buyer mistake | Assuming it covers everything | Assuming any aerospace cert equals process approval |
How to specify this in your RFQ
State the exact certification or accreditation required, and if relevant, the scope. 'NADCAP required' is incomplete if the special process itself is not named. For aerospace, also say whether certification evidence is required at quote stage or only before award.
If suppliers are free to propose an alternate route, say that explicitly. If one process is mandatory because of qualification, source control, or validated history, state that too.
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