How to buy composite structures
In composites the material is made in the shop, at the same time as the part. That one fact drives everything a buyer should check.
A machined part arrives as certified metal and leaves as a shape. A composite part is different: the laminate gets its structural properties during layup and cure, in the supplier's shop, on the day your part is made. The material and the part are manufactured together, so the process control is the product, and a buyer's checks should follow the process.
The accreditations that matter
The industry's answer to process-dependent manufacturing is audited accreditation. Nadcap, the industry-managed accreditation programme run by the Performance Review Institute, covers composites as one of its special-process areas, and the primes require it for the processes they name.1 Ask whether the shop holds Nadcap accreditation for composites, for which processes, and when the last audit was. A general quality certificate, checkable in the IAQG's OASIS database, is the baseline underneath it, naming the site and the scope.3
Material handling is where jobs go wrong
Prepreg lives in a freezer and dies at room temperature, on a clock the material supplier sets. Ask how the shop logs freezer time and out-time per roll and per kit, and ask to see the form it uses. Ask how material lots are tied to serial numbers, so that a lot problem two years from now traces to the parts it touched. A shop that answers with its actual records is telling you how it will treat your hardware.
Design data has its own shared foundation: CMH-17, the composite materials handbook, is the industry's common source of material property data and methodology.2 A supplier doing design work should be able to say which material systems it works in and where the allowables come from.
Tooling, cure and inspection
The tool is a large part of a composite part's cost and schedule. Ask who owns the tool you are paying for, where it is stored, and how its condition is tracked. Ask what cure equipment the shop runs, how thermal surveys are kept current, and what happens when a cure cycle deviates. On inspection, ask what non-destructive testing the drawing calls for, whether it is done in house, and under what accreditation.1
Questions that sort the shops
Ask for the accreditation scope, the out-time procedure, the tool register and one example of a rejected cure and what followed it. That last one is the useful one: every real shop has scrapped parts, and the honest description of a bad day is worth more than any brochure.
The companies below are listed on public facts, each linked to its source. Read the facts, then go and see the freezer.
Sources, in the order cited
- 1Performance Review Institute · Nadcap, industry-managed accreditation for special processes
- 2Composite Materials Handbook 17 · CMH-17, the composite materials handbook
- 3International Accreditation Forum · IAF CertSearch, the global database of accredited certifications