NADCAP Accreditation for Additive Manufacturing: The Special-Process Layer Behind Printed Metal Parts

NADCAP, the National Aerospace and Defense Contractors Accreditation Program, is administered by the Performance Review Institute (PRI) and accredits suppliers' special processes against consensus audit criteria written by industry task groups. It is fundamentally different from a quality-system certificate: a NADCAP auditor spends days on a single process, checking the operation against a published Audit Criteria checklist line by line, witnessing the process, and reviewing job records. The result is accreditation of a specific process to a specific scope, not a general blessing of the company. Additive manufacturing got its own home with audit criteria addressing laser and electron-beam powder bed fusion and directed energy deposition. The audit scrutinizes the things that determine whether a build is repeatable: machine qualification and calibration, parameter control and revision management, powder lifecycle management including virgin-to-recycled blending and sieve and chemistry tracking, atmosphere and oxygen control in the chamber, operator qualification, and the in-process and post-build records. The auditor wants to see that the parameter set is frozen and controlled, that powder is traceable and its reuse bounded by data, and that the shop can reproduce a qualified build rather than relying on a skilled operator's feel. The key point for a buyer is that NADCAP accredits the process as run on specific equipment to specific specifications. A shop accredited for laser powder bed fusion of titanium on one machine type is not automatically accredited for a different alloy, a different machine, or directed energy deposition. The accreditation scope is granular, and reading it precisely is the whole game.

A green additive build is not a finished part, and the processes that make it one are themselves classic NADCAP special processes. Heat treatment relieves residual stress and develops properties and is audited under the Heat Treating task group. Hot isostatic pressing closes internal porosity and is essential for fatigue-critical additive metal; it is audited as a specialized thermal process. Non-destructive testing, especially computed tomography and radiography to verify internal density along with penetrant inspection of surfaces, is audited under the NDT task group. Any machining of mating surfaces and any welding bring their own task-group criteria. The consequence is that 'NADCAP for additive' is rarely a single accreditation. A part that flies typically passes through additive build, stress relief, HIP, heat treat, and CT inspection, and a prime will flow down NADCAP for each special process in that chain. A supplier may hold several NADCAP accreditations in-house and outsource others to accredited subtiers. Either is acceptable, but the chain must be complete: an unaccredited HIP or NDT step is a hole that defeats the entire stack. When evaluating a supplier, map the full process route for your part and confirm an accreditation, in-house or subtier, exists for every special process along it.

NADCAP accreditations are verifiable, which is a major advantage over self-declared statuses. The PRI maintains eAuditNet, the program's online system, where you can confirm a supplier's accreditations, the specific commodities and processes, the scope, and the status and expiration. Always verify there rather than trusting a certificate image. Read the scope at the level it is written: the commodity, the specific process (for example laser powder bed fusion), the materials, the equipment, and the customer or specification approvals tied to it. Watch for scope mismatches, the classic NADCAP trap. A shop may be accredited for one special process but not the one your part needs, or accredited for a process on materials or machines that differ from yours. A lapsed accreditation will show in eAuditNet, and NADCAP runs on a merit-based interval where strong performers earn longer cycles and weaker ones get re-audited more often, so the status and next-audit date tell you something about the supplier's track record. Many primes also maintain their own approved-supplier lists layered on top of NADCAP; if your customer requires a specific prime's approval, NADCAP accreditation is necessary but the prime sign-off may be an additional gate. Verify the live eAuditNet record, confirm the scope matches your exact process and material, and confirm every special process in your part's route is covered.

Because NADCAP audits records as hard as it audits the process, a supplier running an accredited additive operation already generates a thorough paper trail, and you should receive the relevant pieces. Expect the build report with machine identity, frozen parameter-set revision, build date, layer count, and atmosphere and any alarm logs; the powder lot record tying feedstock to chemistry, virgin-to-recycled blend ratio, sieve history, and oxygen pickup; the thermal-process charts for stress relief, HIP, and heat treat showing the actual cycle against the spec; and the NDT reports, including CT density results, against your acceptance criteria. A Certificate of Conformance and material certification tie it together against the applicable AMS or customer specification. Material discipline is where additive NADCAP audits concentrate, because powder is the variable that quietly degrades a process. Reused powder picks up oxygen and changes flow and particle size distribution, and an accredited shop bounds reuse with data and documents the blend behind every build. The common flight alloys, Ti-6Al-4V including the low-oxygen Grade 23, Inconel 718 and 625, and AlSi10Mg, each have specification-driven controls the audit verifies. For the buyer, the practical takeaway is that a genuine NADCAP additive supplier can hand you a build's full lineage, from a specific powder lot through every thermal and inspection step to the finished part, without scrambling, because the program required them to keep exactly those records to pass the audit in the first place.