Coatings and surface treatments

A surface treatment is a special process: one whose result cannot be fully verified by inspecting the finished part. A shiny anodic film will not tell you the bath was in control, a paint thickness gauge will not tell you the pretreatment was right, and a plated part can pass receiving inspection and fail in service years later. The industry's answer is to audit the process rather than the part, and a buyer's checks in this category are mostly checks on paperwork.

Nadcap is the register to read

Nadcap is the industry-managed accreditation programme for special processes, run by the Performance Review Institute and governed by the subscribing primes, which mandate it for the processes they name.¹ Accreditation is granted by task group, chemical processing and coatings among them, each audited against its own criteria, and the working records live in eAuditNet, the programme's audit system.²

Two consequences for a buyer. First, "Nadcap accredited" is an incomplete sentence: accredited for what, at which site, until when. Ask for the scope and check that your process, your specification and the processor's site are on it. Second, an accreditation that lapsed and came back is worth one question, because the story of the gap tells you how the shop behaves under pressure.

Your drawing names the specification, so read it first

Coatings are called out by specification and revision: the anodize type and class, the primer and topcoat system, the conversion coating, the cure schedule. A part processed to the wrong revision is nonconforming even when the finish looks perfect. Ask the processor which revisions its line runs to and check them against the drawing before the first lot, not after.

The chemistry is being regulated out from under you

This is the one category where the process you qualified may become unavailable. Aerospace manufacturing and rework is covered by national emission standards in the United States, which constrain the coatings, solvents and application methods a shop may use.³ In Europe, hexavalent chromium and other substances long standard in aerospace finishing are restricted under REACH, with authorisations that expire.⁴ Ask any prospective processor what it is qualifying as a replacement chemistry, and what it would take to move your part number across. A shop with no answer is a shop that will one day hand you an unplanned requalification.

Scheduling is the hidden cost

Processing is a queue business. A machined part often spends more calendar time waiting for treatment than being cut. Ask for measured turnaround by process, ask your machine shop which processors it actually uses, and ask both what a certified rush costs. Buyers who plan the processing queue into their lead time stop being surprised by it.

Questions that sort processors

Ask for the accreditation scope and its expiry.² Ask which specification revisions the line runs to. Ask how nonconforming work is quarantined and how quickly you would hear. Ask what the replacement chemistry plan is.⁴ The companies below are listed on public facts, each line linking to its source; the scope conversation is shorter when you have read them first.