Aerospace CNC Machining: Alloys, Tolerances and Process Limits

Aluminium is still the default for airframe brackets, housings and ribs. Grades 6061-T6 and 6082 cut fast with good chip control, and 7075 gives higher strength where weight matters more than corrosion resistance. The trade-off is distortion: 7075 and 2024 move after roughing, so heavy stock removal needs a stress-relief step or a rough-and-rest sequence before the finishing passes.

Stainless and titanium behave differently. Grades 304, 316L and 17-4PH (SUS630) are common in actuator parts and fittings; they work-harden quickly, so feeds and speeds must stay aggressive enough to cut under the hardened layer rather than rub it. Ti-6Al-4V (TC4) has low thermal conductivity, which pushes heat into the tool edge. Expect shorter tool life, slower removal rates and higher part cost than the same geometry in aluminium.

Heat-resistant alloys such as Inconel are used for exhaust-side and high-temperature brackets. They are machinable but not cheap: carbide grades need to be selected for the heat, and cycle times can be several times that of stainless. If a part is only lightly loaded, check whether a different alloy would pass before locking in Inconel.

Magnesium AZ31B and AZ91D is the lightest option here. It machines very fast and leaves an excellent finish, but chips are flammable and require dedicated handling. We machine it in separate setups with strict chip control.

• 1
  6061-T6 / 6082Fast, stable, good for brackets and housings.
• 2
  7075 / 2024Higher strength; plan a stress-relief step.
• 3
  Ti-6Al-4VHard on tools, slow, but needed for hot, loaded parts.
• 4
  InconelOnly where temperature demands it; cycle times climb fast.

A 5-axis machine is not simply a faster 3-axis. It lets the tool approach a face at an angle, so undercuts, deep pockets and contoured surfaces can be cut in one setup. For aerospace work that usually means fewer fixtures, fewer datum transfers and a tighter stack-up on features that must stay aligned to each other.

The practical benefit shows up on parts with compound angles, thin ribs or a boss that sits off-axis. On a 3-axis machine those features need multiple repositioning steps, and each step adds a small alignment error. A single 5-axis setup removes most of that error before it can accumulate.

It is not always the right call. Simple prismatic brackets with holes on two or three faces can run faster on a 3-axis mill with a good fixture, because the setup cost is lower and the machine is cheaper per hour. We route work to whichever machine actually suits the geometry rather than defaulting to 5-axis.

Our capacity covers 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers, with a maximum processing size of 4,000 mm and a Ø400 mm rotary table for round work.

Every part is inspected before shipment. The sequence is raw material check, in-process monitoring during cutting, then final inspection against the drawing. Dimensional reports are available on request, and we will work to whichever drawing standard your program uses.

The reason is traceability. A bracket that passes visual inspection can still be out of tolerance on a bore two operations back. In-process checks catch drift while the part is still in the machine, when a correction is cheap instead of a scrap event.

Our quality system holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 certification. The ISO 27001 scope matters for aerospace customers: it covers how we handle your drawings, CAD files and program data. Uploads are treated as confidential, and we sign an NDA on request before files move.

Current qualification rate across production runs is 99.99%. That number is a result of the inspection sequence, not a substitute for it.

Machining wins on low to medium volume, tight tolerances and features that must be cut from solid. It loses on parts where a near-net shape already exists. If a large structural beam is forged or extruded to profile, cutting it from plate wastes material and time and can release internal stress that a forged part already has under control.

Thin walls and tall ribs are another limit. Below roughly 0.8 mm wall thickness in aluminium, chatter and deflection start to dominate, and holding ±0.005 mm becomes unrealistic without custom support. If the design needs paper-thin webs, a different process or a design change is usually cheaper than fighting the cut.

Internal channels that cannot be reached by a tool are a hard stop for milling. Additive processes handle those, then critical faces get machined back to tolerance. We run both, so the recommendation is based on the geometry rather than on what we prefer to sell.

Sheet metal parts, ducts and simple covers are often laser-cut and formed rather than milled. That is a different route with different tolerances, and it is worth checking before a milling quote is finalized.

Anodizing is the usual choice for aluminium airframe parts. Clear, colour, hardcoat and conductive variants are all available. Hardcoat adds wear resistance on sliding surfaces; conductive anodizing keeps grounding paths intact where a standard coating would insulate the part.

For stainless and steel, electroless nickel and plating give corrosion protection without changing dimensions much. Powder coating and black oxide are used on ground-support and non-flight hardware. Bead blasting, tumbling, brushing and polishing are available where surface texture matters.

Laser marking is available with a minimum character height of 1.5 mm. That limit is practical, not arbitrary: below it, legibility drops and the mark becomes hard to read under inspection lighting.

Pick finishes with the service environment in mind. A decorative coating on a part that sees fuel, hydraulic fluid or salt spray will fail early, and the cost of rework is higher than choosing the right finish up front.