Aerospace Machined Parts with 3-Axis CNC Machining: Materials, Documentation and Traceability

An aerospace drawing is bought on its evidence. The alloy must be provable to a heat number and a mill certificate, the machining route must be repeatable, every critical dimension must carry inspection data, and the whole chain has to survive an audit months after the parts landed. If you are sourcing aerospace machined parts from a CNC machining supplier in China, the first question is not whether the tolerance can be held - it is whether the shop can prove that it held it.

The answer to plan around is simple. Aerospace work through a 3-axis CNC machining route is normal for a large share of brackets, housings, and fittings, because most of those parts are prismatic - the kind the machining services list routes by feature count - their features sit on one or two faces. What makes them aerospace parts is not extra axes; it is the material contract and the documentation contract. Nail those two, and the machining is a precision metal-cutting job like any other; skip them, and no five-axis machine in the world saves the program.

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

Geometry is rarely what changes. A commercial bracket and an aerospace bracket can be cut with the same toolpaths on the same machine class. What changes is the obligation around the part: every material claim must be verifiable, every critical dimension must carry inspection evidence, every process change must be documented, and the record must survive reconstruction after shipment. Aerospace sourcing is evidence management with machining attached.

That reframes supplier selection. A shop that machines well but treats paperwork as optional is a liability on an aerospace program, because the failure mode is the record that cannot be produced when the auditor asks. A shop with tidy documents but ordinary capability fails the part instead. Both halves must be present, and you should test them in that order - evidence first, then geometry.

It also changes the quoting conversation. Aerospace drawings carry revision control, material condition, and inspection frequency requirements that all have cost and lead time attached. A supplier that quotes an aerospace drawing without asking about the FAI format, the documentation package, or the inspection frequency is not quoting the job you are buying. The questions a shop asks are the first evidence of whether it understands the program it is bidding on.

Which aerospace alloys and tempers should the drawing name?

The aerospace material list is short, and the condition attached to each grade is where sourcing errors start. Aluminum appears as 6061-T6 for general structure and 7075-T6 for higher loads, with -T7351 chosen where stress-corrosion resistance matters. Stainless shows up as 17-4PH and 15-5PH, machined in the annealed or solution-treated condition and aged after machining to the specified strength. Titanium is dominated by Ti-6Al-4V, with the ELI variant for fracture-critical parts. Inconel 718 covers the hot sections. PEEK covers the polymer corners where weight and chemical resistance beat metal.

Each entry changes the machining route in a specific way. 7075 machines harder and costs more than 6061. Aged stainless needs heat treatment sequenced between roughing and finishing. Titanium is slow, expensive, and demanding on tooling. Inconel is the hardest on every axis - cost, cycle time, and tool wear. And PEEK is a polymer with polymer behavior, cut with different tooling and feeds entirely. The drawing that names grade and condition is the drawing that can be quoted; the drawing that leaves them open makes the shop guess, and the guess is priced in.

For a 3-axis route specifically, the material decides which parts stay on the cheap machine. A 6061 bracket with all features on one face is 3-axis work at its most economical. A 17-4PH fitting with features on several faces may still run on a 3-axis machine with indexing, but the material and the setups both add cost. The material choice and the axis choice are one decision, and aerospace buyers should make it deliberately rather than inherit it from an old drawing.

What tolerances are realistic on aerospace parts - and where should they sit?

Aerospace parts are tight where function demands and ordinary elsewhere. Bores that carry bearings, faces that seal, and features that locate other components carry the critical callouts, verified against a datum reference frame on a CMM. Everything else runs to general tolerance, because a wall of tight dimensions buys inspection hours without buying function.

What precision machining holds is well established: ±0.003 mm on milling and ±0.002 mm on precision grinding, with process capability targets such as Ppk ≥ 1.67 at the initial study on key characteristics and Cpk ≥ 1.33 on general characteristics. Capability is reported per characteristic: every report names the feature, its tolerance band, the sample size, the sigma method, and the study window. The realistic question is the geometry around each callout. A tight bore in 6061 is routine; the same bore in a thin-walled Inconel housing is a process-development project. A tight flatness on a large titanium plate fights residual stress and temperature. The tolerance is only as honest as the material and the process behind it.

The 3-axis twist is the setup question. A tolerance that crosses two setups - a feature on the front face controlling one on the back - depends on how accurately the second setup finds the datum of the first. On an aerospace drawing, review which critical tolerances cross faces, because those are the ones that argue for indexing, an extra axis, or a single-setup design. Concentrate the tight callouts where they function, and ask the shop how the ones that cross setups will be held and measured.

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

The baseline document is the material certificate: heat number, grade, condition, and the chemical and mechanical values from the mill or distributor, naming the specification the material was produced to. On aerospace work it should arrive with the parts or before them. A certificate that names a different grade, carries an unreadable heat number, or shows values that miss the drawing requirement is a flag, not a document.

What separates a serious machining supplier is the step before the certificate is filed: verifying the delivered lot against the certificate, so the heat stated is the heat machined. This incoming check catches substituted or mixed alloys, and it is the most valuable material control you can insist on, because no downstream inspection can detect that the wrong alloy was in the machine. Ask how incoming stock is confirmed and what happens when a check fails.

Be realistic about what to expect. The mill certificate and the verification record are standard; the shop re-certifying material it did not produce is not. If the program demands heat-level traceability across multiple parts, say so at quoting, because segregated lots and heat-level records change how the run is planned and priced.

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

A first-article inspection verifies every characteristic on the drawing against the approved configuration, usually on the AS9102 form or the customer's equivalent. The machining shop produces it at the first article, with the dimensional data behind each characteristic and the drawing revision it was measured against. This is where the tolerance callouts become evidence instead of intentions.

On a sourced job, the FAI is only as good as its review. A document arriving by email is a claim; the review that checks the datum scheme, the sampling, and the measurement method against the drawing is the control. For critical features the CMM data should be readable - which datums were used, how the feature was aligned, and what was measured - not a pass/fail stamp with no numbers behind it.

Sequence the FAI before production, not after. A supplier that machines the full run and produces the FAI afterward has turned first-article inspection into last-article confirmation. The professional sequence is first article, full inspection, FAI issued, buyer review, then release of the remaining quantity. That gate is what de-risks a sourced aerospace part, and a supplier's willingness to hold it predicts how the rest of the relationship runs.

Which certificates should the machining company hold, and where does AS9100 sit?

Certification is the cheapest pre-qualification you can run, because it proves a documented, externally audited quality system exists. For a build-to-print machining supplier serving aerospace through an upper tier, the meaningful certificates are ISO 9001:2015 and IATF 16949:2016 for the quality system, plus ISO 14001:2015 for environmental management. All three should be current, and their scope lines should cover machining.

AS9100 is the aerospace quality standard, and it sits one step up the chain. If your contract requires machining at an AS9100-certified site, nothing else substitutes, and the certificate must be verifiable with the registrar. But much aerospace machining flows through primes and tiers that hold AS9100 and release work to build-to-print suppliers under their control plans - and in that structure, a shop certified to ISO 9001 and IATF 16949 can carry the machining while the upper tier owns the aerospace system obligation.

your job is to know which structure applies before quoting. Ask whether the program requires AS9100 at the machining site or accepts an upper-tier control plan, and ask the supplier to state its certification scope plainly. A certificate number on a website is marketing; a current certificate with a matching scope, confirmed against the registrar, is evidence.

What should the inspection and evidence package contain when the parts land?

When aerospace parts arrive, the part and its package should tell the same story. At minimum the package carries the dimensional report for the critical characteristics, the material certificate, and a statement of conformity to the drawing revision. A serious program adds the FAI package, SPC charts where key characteristics were process-monitored, and a record of any non-conformance and its disposition.

Read the package as a chain, not a pile of papers. The material certificate should match the heat on the traveler; the dimensional report should reference the same drawing revision as the FAI; the SPC charts should name the same characteristics as the critical callouts. Gaps between documents are where sourcing risk hides, and reconciling the package before payment catches more problems than inspecting the parts alone.

Two practical checks make the package useful. Confirm the drawing revision on every document matches the revision you released - a package built against an outdated revision is worse than none. And file the evidence against the part identity rather than the purchase order, so a specific lot or serial can be pulled months later. That is the traceability an auditor actually tests.

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

The first order is a qualification exercise wearing a purchase order. Use it to test what a brochure cannot: whether the supplier machines the drawing as released, produces inspection data that reconciles, ships the documentation with the parts, and answers hard questions without friction. The evidence from that order, not its price, decides whether the program scales.

Run the qualification in stages. Send a representative part with real critical callouts and demand the full package. Have the FAI reviewed independently - by your own engineer or a third-party inspector who knows aerospace drawings. Verify the certificates against their registrars, and confirm the incoming material check happens the way it was described. If the program justifies it, audit the factory in person or by live video before the production release.

A supplier that clears that bar on the first order earns the volume on evidence. One that clears it only on price will cost you the difference later, in rework, expediting, or an audit finding no tolerance band can cure. Aerospace sourcing is a long game played one qualification at a time - and if you treat the first order as a test, you are the one whose production runs arrive on evidence, not on hope.

What this shop actually runs

Capability evidence should come as specifics, not slogans. Behind this guide is a 6,800 m2 plant in Dongguan, China running 100+ CNC machines with 100+ staff. The machine list by category:

• 5-axis machining centres (10+) - Mazak VARIAXIS I-600 (510/910/510 mm travel, 12,000 rpm, 22 kW, 71.6 N·m, 30-tool BT40) and Mazak INTEGREX I-250H S (B-axis 0.0001°, 24 kW, 124 N·m, 38-tool HSK-A63). Cut on compound-angle parts, single-setup multi-face prismatic work, and aerospace fittings where datum transfer loss is unacceptable.
• 3-axis / 4-axis machining centres (50+) - Brother SPEEDIO S500Z2N / S700Z2N (10,000 rpm, 14/21-tool ATC, 0.7 s tool-to-tool, Z-axis 2.2 G) and Mazak VCE-430A L / VCE-570C L (10,000 rpm, 118 N·m, 24-tool ATC). Cut on prismatic parts, plates, brackets, housings.
• Swiss-type turning centres (10+) - Citizen Cincom A20-3F7 (Φ20 mm, 10,000 rpm), TSUGAMI B0206-III / B0205-III (Φ20 mm, 0.1 µm), STAR SR-32JII / SR-32J Type N (Φ32 mm, 8,000 rpm). Cut on long, slender rotational parts at ±0.002 mm.
• CNC turning centres (20+) - HEADMAN T70M/1250 (720 mm swing, 117 mm bore, 3,000 rpm, BMT75 12-station turret). Cut on shafts, bushings, flanges up to ±0.002 mm.
• Wire EDM (5+) - Sodick AQ535L (550/350/300 mm travel, ±20° taper, 800 kg workpiece). Cut on hardened tool steel, internal splines, sharp internal corners that milling cannot reach.
• Inspection: Hexagon CMM + 20+ gauges - Hexagon CMM for coordinate measurement, plus vision system, profilometer, hardness tester, coating thickness gauge, XRF for material verification. The 10:1 rule (gauge 10x more accurate than the band) is applied to every feature.
• Machine highlights - VARIAXIS I-600: one-setup multi-face 5-axis + MAZA-CHECK auto-calibration; INTEGREX I-250H S: DONE-IN-ONE mill-turn, B-axis 0.0001° + Ai thermal shield; SPEEDIO S500Z2N / S700Z2N: Z-axis 2.2 G + 0.7 s ATC; Swiss-type: guide-bush switchable + 0.1 µm resolution.
• Aerospace routing - VARIAXIS I-600 (5-axis) for blisks, impellers and structural brackets; INTEGREX I-250H S (B-axis 0.0001°) for turbine blades and shafts; Swiss-type lathes for fittings and pins.

Tolerance: ±0.003 mm CNC milling / ±0.002 mm CNC turning / ±0.002 mm grinding and wire EDM. Capability: Ppk >= 1.67 initial on key characteristics, Cpk >= 1.33 ongoing.

Certificates: ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, with design clause 8.3 excluded, stated openly) and ISO 14001:2015 (116024/B/0001/UK/En), issued to Dongguan Zhuohang Ltd, registration 91441900MA4UWT6X39, founded 2005.

Where we ship: Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa — plus other countries and regions worldwide, shipped from our base in Dongguan, China.

Contact: Felipe Iglesias, [email protected], +86 13126536955.

Frequently Asked Questions

Standards referenced on this page

• ASTM B211/B211M-19 — Standard Specification for Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire
• ASTM B348/B348M-21 — Standard Specification for Titanium and Titanium Alloy Bars and Billets
• ISO 9001 — Quality management systems — Requirements