Aerospace Manufacturing Processes Reference

How to use this section

Start with the process your part depends on most, then follow the links to the steps before and after it. Most quality escapes in aerospace supply chains happen at the handoff between processes, not inside one: a part plated before it was baked, a bore anodized without a pre-finish allowance, a stainless part passivated after it was precision cleaned. The pages are written to make those handoffs visible.

Every page lists its sources. Where a number comes from a supplier or a secondary source rather than the specification itself, the page says so. Specifications are revised often, so treat any revision letter here as a pointer and check the current issue before writing it on a drawing.

The process pages at a glance

Special processes and why they get extra control

In aerospace quality systems, a special process is one whose result cannot be fully verified by inspecting the finished part. Heat treatment, plating, anodizing, chemical conversion coating, welding, NDT and composite cure all qualify. You cannot measure a part and confirm it was solution treated at the right temperature, or that a weld has no lack of fusion below the surface, or that a laminate saw its full cure. The only assurance is a controlled, qualified process with records.

That is why primes approve special process sources individually, and why many require accreditation through Nadcap, administered by the Performance Review Institute. Nadcap audits are organized by commodity, each with its own audit criteria. The ones engineers meet most often:

Two practical points. First, accreditation is granted by scope, so read the certificate rather than trusting a logo. Second, Nadcap does not replace your customer's approval. Many primes keep their own list of approved processors by specification, and a Nadcap accredited shop that is not on that list can still cause a rejection.

Typical process routes

Seeing a whole route makes the sequencing rules concrete. These are representative examples, not prescriptions. Your drawing, material spec and customer requirements decide the actual route.

What to put on the purchase order

Drawings define the part. The purchase order defines how the supply chain must behave while making it. For aerospace work the PO quality clauses usually carry:

• Specification revisions in effect, or a statement that the latest revision on the PO date applies
• Approved source requirements for special processes, including Nadcap and any customer approval list
• First article inspection to AS9102, and the triggers for a new or partial first article
• Certificate requirements: material certs traceable to heat or lot, process certs per operation, and a certificate of conformance
• Right of access for you and your customer to the supplier's facility and records
• Notification of changes to process, location or sub-tier sources
• Record retention period
• Export control marking and handling requirements where applicable

Missing clauses are the reason many shops ship parts with incomplete paperwork. They were never asked for it. If your quality group has standard clauses, attach them to every order rather than relying on a general reference.

The certificate package

Each process leaves a record, and the set of records is how a part proves its pedigree. A complete package for a machined, heat treated and finished part might contain the material cert from the mill, the heat treat cert with furnace and cycle identification and hardness or conductivity results, the finish cert with spec, type, class and thickness, NDT reports with method, procedure, acceptance criteria and inspector certification, the dimensional report or AS9102 first article, and the supplier's certificate of conformance tying them together.

Check that every record names the same part number and revision, that heat or lot numbers carry through, and that dates are in a plausible order. A finish cert dated before the heat treat cert on a part that must be heat treated first is a finding. Receiving inspection practice is covered on the receiving inspection page.

What drives lead time across processes

Process steps add lead time mostly through queues, not processing hours. Each outside special process means a ship out, a queue at the processor, the process itself, the cert and a ship back. Batch processes such as heat treat and plating often wait to fill a load. Accredited processors for less common specs may be few, and their queues set your schedule. First article adds inspection and review time on the first lot.

Engineers can shorten lead time by allowing equivalent specifications where the program permits, avoiding exotic finishes on non critical surfaces, buying material already in the final temper when possible, and freezing the drawing before release so changes do not restart special process routing. For more on scheduling, see lead times and delivery.

Design choices that simplify the process chain

Many process headaches are designed in. A few habits at the drawing board remove whole steps or whole suppliers from the route:

• Limit finishes to where they are needed. A hard anodize callout on the whole part when only one bore needs wear resistance adds masking or growth allowances everywhere else.
• Choose materials that avoid a process. Buying plate or bar in the final temper can remove an outside heat treat step, as long as the machining does not depend on a softer condition.
• Avoid mixing incompatible requirements on one part. A high strength steel part that also needs electroplating brings a mandatory bake and its timing limits. A different alloy or coating may avoid both.
• Design for inspection. A weld or an internal channel that cannot be inspected forces either a more expensive method such as CT or a lower allowable.
• State the intent in notes. If a feature is a sealing surface, a grounding point or a fatigue critical area, say so, because each changes how the supplier finishes and inspects it.

A short design review with a manufacturing engineer before release usually catches these. It costs less than a requalification after the first lot.

Materials and machines

Process choices are tied to material choices. Titanium raises alpha case and welding shielding questions, high strength steels raise hydrogen embrittlement and grinding burn, aluminum alloys differ widely in anodize response, and nickel alloys drive tool wear and EDM recast concerns. The materials section covers alloys, tempers and certification. The machines section covers machine classes, work envelopes and how to judge whether a shop can hold your part.

Controlled data and these processes

Many process sources handle export controlled drawings and models, and the process specifications themselves are usually public, but the part data often is not. ITAR and EAR controlled technical data must only reach authorized U.S. persons and authorized suppliers. If your part is controlled, read how we handle controlled programs before sending anything. Controlled data never goes through the website.

Get a process chain sourced

Most parts need more than one source: a machine shop, a heat treater, a finisher, an NDT lab and sometimes a cleaning house. Send the drawing and specs and we source the whole chain from qualified suppliers, flow down the requirements to each one, track the job, check every cert against the PO and deliver with the certificate package. A person replies within one business day, and we sign a mutual NDA before files.

In this section

• Composites Fabrication for Aerospace Structures
• EDM and Precision Grinding for Aerospace Parts
• 5-Axis CNC Machining for Aerospace Parts
• Aerospace Heat Treatment: Pyrometry, Process Specs and Callouts
• Inspection and Metrology for Aerospace Parts
• Metal Additive Manufacturing for Aerospace Hardware
• Nondestructive Testing for Aerospace Parts
• Precision Cleaning and Oxygen Service Cleaning
• Sheet Metal Forming and Aerospace Welding
• Aerospace Surface Finishing: Specs, Callouts and Pitfalls
• CNC Turning and Swiss Machining for Aerospace Parts

Questions

Related

• Aerospace Heat Treatment: Pyrometry, Process Specs and Callouts
• Aerospace Surface Finishing: Specs, Callouts and Pitfalls
• Inspection and Metrology for Aerospace Parts
• 5-Axis CNC Machining for Aerospace Parts

Sources

• Performance Review Institute: Nadcap
• JAQG: Nadcap audit criteria list
• ASME: Y14.5 Dimensioning and Tolerancing
• Ideagen: AS9102 Rev C template and guide
• AWS Welding Digest: aerospace welding specifications
• NASA: NASA-STD-6030 Additive Manufacturing Requirements for Spaceflight Systems
• SAE: AMS 2759/9E hydrogen embrittlement relief baking
• NASA Technical Standards: MSFC-SPEC-164 Rev E