Aerospace Machined Parts from a Precision Machining Factory: Materials, Documentation and Traceability

Aerospace machined parts from China are usually bought by an engineer or NPI lead who holds a drawing, a material callout and a supplier quality clause, not by a purchasing department with a page of vendors. The order succeeds or fails on four decisions made before any metal is cut: the material grade and condition named on the drawing, the tolerances allocated to the features that function, the documentation written into the purchase order, and the certification and first-article gates that control the first lot. This guide walks each decision from the buyer's side, and it is direct about where aerospace certification requirements actually sit in the supply chain.

What changes when a machined part is headed into an aerospace program?

Aerospace parts carry an administrative load that the same geometry would not carry in a less regulated market, and most of it lands on the buyer before it lands on the factory. The prime flows its supplier quality requirements down the chain, which makes your purchase order the document that controls the machining: which alloys are acceptable, whether substitutions need written approval, what records accompany each lot, how a nonconformance is reported, and how long the records are kept. Understand which clause of your contract imposes these duties before you start comparing factories.

None of this means the parts are exotic. Brackets, housings, fittings and actuator components are ordinary machined parts that happen to sit inside a controlled system, and the discipline they demand is straightforward: the alloy received must be the alloy specified, the measured result must match the reported result, and a deviation another industry might absorb becomes a documented event. A precision machining factory working inside a certified quality system treats this as the baseline, which is why the factory's quality system and its inspection bench matter more to your program than any single part it ships.

Which alloys and tempers should the drawing name for aerospace machined parts?

The grade line is where most aerospace material disputes start, because one common name covers materials with different properties. 6061-T6 is the workhorse for brackets and housings — stable, free-cutting, anodizes cleanly. 7075 brings higher strength but carries residual stress unless the stock is specified in a stress-relieved condition such as -T7351, so on thin machined-away sections the condition line matters more than the alloy line. A drawing that says only "7075" has delegated a metallurgical decision to someone who should not be making it.

Stainless and the high-temperature alloys demand the same precision. 17-4PH is machined in Condition A and aged to H900–H1150, and the drawing must name the condition or the heat-treat step is undefined — a step almost always performed by a certified specialty partner rather than on the machining floor. Titanium Ti-6Al-4V and nickel alloys such as Inconel 718 add machining time, chip-control care and material cost, so they appear on the drawing with the specification standard they must meet. Name the grade, the condition and the standard — AMS, ASTM or an acceptable equivalent — and state whether deviations are permitted. That single line removes the largest source of aerospace material disputes before any tool touches the work.

Alloy / condition	Typical aerospace use	What the buyer should pin down
6061-T6	Brackets, housings, panels, non-structural fittings	Anodize class if finished; temper confirmed on the certificate
7075-T6 / -T7351	Stressed structural sections	Stress-relieved stock; distortion limits on thin walls
17-4PH (H900–H1150)	Fasteners, valve and actuator hardware	Heat-treat condition and the certified partner performing aging
Ti-6Al-4V (Grade 5)	Airframe and engine components	Lot origin documentation; machining cycle priced realistically
Inconel 718 / 625	High-temperature hardware	Spec standard; work-hardening effects on tooling and cost

Which tolerances are realistic on aerospace machined parts, and where should tight ones go?

Measurement discipline is half the tolerance story. Ask which characteristics are inspected 100% and which by sampling, what instrument measures each critical feature, and what happens when a sampled lot drifts toward a limit. On thin-wall aerospace features the answer also depends on the conditions of measurement — temperature-controlled benches, calibrated probes, fixtures that do not distort the part — because a part measured while it flexes tells you nothing about the part in service. The factory that answers with a control plan has a method; one that answers with assurances has a hope.

The capability band a precision machining factory should state without hedging is ±0.003 mm on milling and turning and ±0.002 mm on precision grinding, with process capability of Ppk ≥ 1.67 at the initial study on key characteristics. That is the design ceiling for the features that carry function — bores, dowel locations, sealing surfaces, the datum faces the assembly builds on — and it is not the right number for every dimension on the drawing.

Tolerance is a budget, and it should be spent where the assembly spends it. Use geometric tolerancing — position, flatness, parallelism — rather than blanket ± callouts, because GD&T tells the factory what the feature must do instead of what an arbitrary number should be. Expect the design-for-manufacturing review to push back before cutting: a factory that flags a callout it cannot hold reliably at your quantity, and proposes the fix in the quote, is doing the engineering with you. One that quotes every dimension at its tightest without comment is pricing the risk it plans to take, not removing it.

What material documentation should you request, and what is realistic to receive?

For machined aerospace parts the deliverable stack is a certificate of conformance for the lot, a mill material test certificate matching the heat number actually received, and — where the drawing or quality clause calls for it — evidence that the incoming material was verified against that certificate rather than trusted on paper. Positive material identification is an industry-standard request on critical alloys; if you specify it, name the method and the acceptance frequency in the purchase order so the quote reflects the added verification.

Traceability is the step that separates aerospace paperwork from ordinary shipping documents. Where the drawing requires it, the heat number must be recorded against serialized parts so a material question at assembly can be answered backward. Ask the factory in writing how far its lot traceability reaches, how records are kept and for how long, and request a sample certificate-and-traceability package during quoting — before the first order, not after the first nonconformance. A factory that answers with a document flow has built the system; one that answers with assurances is describing the system it hopes to have.

How do first-article inspection and FAI paperwork work on a China-sourced job?

Agree the record format before the first shipment. Aerospace receiving teams work faster when the package arrives as they expect it — the certificate of conformance, the material certificate, the dimensional report and the SPC data named in the purchase order, in a consistent digital format with the lot number on every page. Ask the factory how it packages and retains these records, and confirm the retention window matches your contract clause, because the report you need at an audit three years from now is the report that has to exist on the factory's server, not in a drawer that was cleared.

First article inspection is a program gate, and the form aerospace programs expect is the industry-standard AS9102. It is not something every factory keeps on its price list, because it is a requirement your contract flows down when the end customer demands it. The buyer should ask in the RFQ whether the factory completes the dimensional and process sections of the FAI against the drawing, and should request a completed sample to confirm the format is understood before the order exists. On a machined part the FAI tells the geometry story — each characteristic against its instrument, each surface finish against its method, each datum relationship against the drawing's definition.

Plan for delta FAIs too. A change to design, material, process or tooling that affects fit, form or function requires a re-issue limited to the affected characteristics, so the purchase order should carry a change-notification duty that stops a silent process revision from invalidating your approval. Treat the FAI as a living document attached to the part's history, reviewed before the production release and reopened whenever the process changes.

Which certificates should the factory hold, and where does AS9100 sit in the chain?

The baseline for a serious precision machining factory is ISO 9001:2015 for the quality management system, with IATF 16949:2016 (product design excluded) and ISO 14001:2015 alongside where it serves regulated industrial programs. Those certificates should be provable by number and scope through the registrar — a certificate without a verifiable number and scope is decoration. Ask for the numbers and the scope statements, including any exclusion of design responsibility, because a build-to-print factory machines to your drawing and should say so plainly.

AS9100 deserves plain language about its place. It is the aerospace-specific system required of the organization that holds aerospace purchase orders directly, and a sub-tier machining factory can legitimately work under the buyer's or prime's AS9100 system with the buyer controlling the supplier. Ask directly whether your order requires AS9100 at the factory's level, and if it does, request the certificate number, scope and registrar to verify rather than accepting a claim. If the factory is a sub-tier under your system, your own supplier-control process governs. A factory that answers this question in one sentence, without hedging, has told you more about its quality culture than any brochure will.

What should the inspection and evidence package contain on a machined aerospace part?

Verifying a certificate is a ten-minute task once you have the number: the registrar's directory or a direct confirmation email settles whether the certificate is live and what the scope covers. Make it part of the RFQ routine rather than a step you take only for the finalist, because checking every candidate catches the supplier whose certificate expired between the site and the quote. A factory that tells you its certificate is in renewal without the paperwork in hand has told you how it manages other deadlines too.

Expect — and write into the purchase order — a dimensional report per characteristic with nominal, actual and deviation; SPC on key characteristics reported against the Ppk ≥ 1.67 initial-study target; the material certificate chain; surface-finish readings where the drawing calls them out; and process records where heat treatment or surface treatment was applied by a specialty partner. The report should name the instruments and their calibration status, because a dimension is only as credible as the tool that measured it and the datum setup that defined it.

Ask for a sample report at the RFQ stage and judge it like an auditor. Are the values actual measurements or a printed claim? Are the datum references the same as the drawing's? Can the numbers be traced to the specific parts in the lot? The factories that survive aerospace audits ship packages that already look like this, because their standard process produced the evidence. If the sample package is vague, the production lots will be vaguer.

How do you de-risk the first aerospace order before committing to volume?

Run the first order as a controlled pilot even when the quantity is small. Release a limited lot with the FAI requirement, the full drawing set and your quality clause written into the purchase order, and hold shipment until the inspection package arrives and is reviewed. Where the program allows, add source inspection — a visit or a documented video walkdown of the critical characteristics at the bench — so the evidence is verified where the parts are, not after a container has crossed an ocean.

Agree the exception path before it is needed: how a nonconformance is reported, who approves a deviation, and what happens to discrepant parts. A factory that already works an NCR and disposition flow answers these questions with its standard procedure and a reference lot, which is the signal that the first order is in the right hands. The pilot exists to prove the drawing, the process and the documentation at a scale you can afford to learn from; the volume order is simply the pilot that already passed.

Frequently Asked Questions

Can a precision machining factory in China supply aerospace parts without holding AS9100?

In a sub-tier role, yes. Build-to-print machining orders commonly flow under the buyer's or prime's AS9100 system, with the factory operating its ISO 9001:2015 quality system against your controlled requirements. If your contract requires the factory to hold AS9100 directly, verify the certificate number and scope with the registrar before you rely on it.

What tolerance should I expect on aerospace machined parts?

±0.003 mm on milling and turning and ±0.002 mm on precision grinding, with process capability of Ppk ≥ 1.67 at the initial study on key characteristics. Reserve the tight band for functional features and use geometric tolerancing elsewhere so cost stays where the risk is.

Which material certificate matters most on an aerospace order?

The mill material test certificate tied to the heat number actually received. On critical alloys, specify positive material identification where the drawing or quality clause requires it, and ask how far lot traceability runs — from incoming heat to serialized finished part.

Who fills out the AS9102 first article form?

The party your contract makes responsible. Typically the factory completes the dimensional and process sections against your drawing under your quality clause, and you review and approve before the form flows upward. Confirm the split in the RFQ and request a completed sample before the order.

Should every dimension on an aerospace drawing be held to ±0.003 mm?

No. Tight tolerances belong on features that mate, seal or define assembly datum structure; blanket tight callouts add cost and inspection burden without adding function. A good factory flags over-tolerancing in the design-for-manufacturing review rather than quoting it silently.

What is a delta FAI and when does it apply?

A re-issue of the first article report limited to affected characteristics, triggered by a change to design, material, process or tooling that affects fit, form or function. The purchase order should carry a change-notification duty so a silent process revision cannot invalidate your original approval.

Do I need to visit the factory before the first aerospace order?

Not for a controlled pilot. Release a limited quantity with the FAI requirement and your quality clause, review the inspection package before shipment, and add source inspection where the program allows. A visit belongs to the stage when volume and long-term supply justify the trip.