Not all coating companies are allowed to coat parts for aerospace and defence! There are specific approval processes in place that need to be followed for each specific coating process, and approving the wrong coating process for a particular part can result in that part being grounded.
What OEM and NADCAP Approval Means
OEM approvals mean that Aerospace Surface Treatment providers have been audited by the Aircraft or Engine Original Manufacturer and approved as an “approved processor” on the manufacturer’s approved list. NADCAP (National Aerospace and Defence Contractors Accreditation Program) approval is an industry wide approval body, audited to a fixed checklist (developed by the Performance Review Institute). Many Original Equipment Manufacturers (OEMs) accept NADCAP approval as a minimum requirement for surface treatment processes, although approval by the OEM is preferred.
How Specifications Appear on Drawings
An engineering drawing will “Call out” a specific process in a specification, for example, AMS 2404 for an electroless nickel coating or AMS 2468 for a hard anodising coating. The approved supplier must have approval for that specific number process specification. Although there may be other processes in the same family that are similar but have different specification numbers they will not satisfy the callout and would require a formal deviation to be issued before the process could be used on production parts.
What First-Article Testing Proves
Before new suppliers or process variants can be released to production, first-article testing of coated components must be conducted to check if the required mechanical properties as well as chemical characteristics (e.g. thickness, adhesion, hardness, corrosion resistance) are met. Test coupons are produced in addition to the actual components to be coated. The test results are stored on file as reference.
Keeping Approvals Live
Approvals do not last indefinitely. Periodically your supplier will be visited by your OEM auditor, monitoring if the required process is still under control. Even more frequently the required coupon tests are scheduled. These so-called Interim Release tests are used to prove that new processing variations still meet all mechanical and chemical requirements.
Checking a Supplier’s Scope Before Ordering
Request to view the current approval certificates for the specified process(s) within the scope of approval for any potential supplier(s) for Aerospace and Defence coating work. There is more on Aerospace Surface Treatments at www.poeton.co.uk/about/industries/aerospace-defence/.
A Certificate of Conformance confirms that your Aerospace Surface Treatments have been carried out within the approved scope.
