CNC Machining Aerospace Parts

• 1
  What Makes Aerospace Parts Different to Machine
• 2
  Alloy Selection and Its Machining Consequences
• 3
  Where 5-Axis Setups Change the Result
• 4
  Tolerance, Surface Finish and What They Cost
• 5
  Fixturing, Distortion and Cutting Sequence
• 6
  Inspection and Traceability for Flight Hardware
• 7
  Matching Material and Machine to the Part

Aerospace parts are judged on three things at once: mass, stiffness and fatigue life. That combination drives the geometry. You see thin walls, deep pockets, long slender ribs and bosses that carry load in one direction only. Every one of those features moves under cutting force, which is why the machining plan matters as much as the drawing.

The material usually makes it harder. 7075 aluminium cuts clean but distorts after heat treatment. Ti-6Al-4V has low thermal conductivity, so heat stays in the cutting zone and tool life drops fast. 17-4PH stainless in the H1025 condition is tough on edges. Inconel is worse again. None of these behave like mild steel.

So the first question on any new job is not which machine, it is how much material has to come out and how much the part is allowed to move. A bracket with 60 percent stock removal behaves differently from a housing that is mostly a shell.

• 1
  Mass drives geometryLightening pockets leave thin floors that deflect during roughing.
• 2
  Material drives tool lifeTitanium and Inconel need lower surface speed and more coolant.
• 3
  Heat treatment drives sequenceFinish cuts after stress relief hold size far better.

Most airframe brackets and housings we machine are aluminium: 6061-T6, 7075, 2024 and 6082. The 6000 series welds and anodizes well and holds a good finish. 7075 gives roughly twice the yield strength but is less corrosion resistant and more sensitive to stress corrosion cracking at exposed edges. 2024 machines nicely and fatigues well, though it needs cladding or coating in most service conditions.

Where temperature climbs, titanium takes over. TC4 (Ti-6Al-4V) is the common choice, with TA1 and TA2 used for lower-strength ductile parts. Titanium cuts at roughly a third of the surface speed you would use on aluminium, and it work-hardens if the tool rubs instead of cutting. Feed per tooth has to stay high enough to keep the edge engaged.

Stainless 17-4PH covers actuator parts and fittings, while 303, 304 and 316L appear in fluid and ground-support hardware. Inconel shows up in exhaust-adjacent components. On those jobs the cutting parameters are conservative and the tool changes are frequent, and that is priced into the quote.

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  Aluminium 6061-T6General brackets, covers, housings. Easy to machine, easy to anodize.
• 2
  Aluminium 7075High-load fittings. Higher strength, poorer corrosion resistance.
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  Titanium TC4Hot sections and high-stress fittings. Slow cutting, short tool life.
• 4
  17-4PH stainlessActuator and fitting parts. Good strength, moderate machinability.

A 3-axis machine reaches a part from one direction. That is fine for plates, covers and shallow pockets. The moment a part has features on five faces, or a contoured surface that would need many shallow passes, the setup count on 3-axis work climbs and each re-fixture adds position error.

A simultaneous 5-axis center keeps the tool normal to the surface and reaches undercuts that 3-axis cannot. For a contoured impeller or a duct with a curved flange, this cuts cycle time and removes the stacked tolerances of four separate fixtures. It also lets you use shorter tools, which reduces chatter on deep ribs.

It is not always the right call. A flat plate with holes is cheaper on a 3-axis machine and just as accurate. Reach and access decide the machine, not the part's industry label. If a 3-axis setup plus a simple angle fixture holds the tolerance, use it.

Our shop runs 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers, with a Ø400 mm rotary table for round work and up to 4,000 mm of travel on the largest frames.

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  One setup, more facesFewer re-fixtures means less stacked position error.
• 2
  Shorter toolsTool axis control lets you reach deep ribs with a stiffer cutter.
• 3
  Not automaticSimple prismatic parts stay cheaper on 3-axis.

Tolerance is a process decision, not a wish. Our working tolerance is ±0.005 mm (±0.0002 in) on features that need it. Applying that number across an entire drawing is expensive, because it forces slower passes and more inspection on features that may not matter.

A practical approach is to tolerance only the interfaces: bearing bores, dowel holes, mating faces, seal grooves. A pocket floor that holds a bracket can sit at ±0.1 mm without any loss of function. Mark the datum scheme clearly and the whole part gets easier to hold.

Surface finish follows the same logic. As-machined surfaces sit around Ra 1.6–3.2 μm. A high-quality finish is Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm. Going finer usually means a separate finishing pass or a secondary operation. Specify it only where a seal, bearing or airflow actually needs it.

• 1
  Tolerance the interfacesBores, dowels and mating faces carry the tight callouts.
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  Leave the rest openNon-critical pockets can sit at ±0.1 mm.
• 3
  Finish where it worksSeals and bearing journals justify fine finishes.

Thin-wall aerospace parts fail on fixturing more often than on machine accuracy. Clamp a thin rib too hard and it springs back when released. The cut looked perfect on the machine and the part is out of tolerance on the bench.

The usual fix is to rough, stress relieve, then finish. Roughing removes the bulk of the stock while the part is still stiff. Stress relief or a controlled aging step lets the material settle. The finish pass then takes light cuts, around 0.2–0.5 mm radial engagement, so the cutting force stays low and the wall does not deflect.

For very thin floors we use support material, sacrificial tabs or low-melt fixturing, and we often leave a light finishing allowance on both sides so the part is cut symmetrically. Symmetric material removal is the single most effective way to keep a thin part flat. If a design can be mirrored around its neutral axis, do it.

Early communication about tolerances tighter than ±0.005 mm helps here. Those callouts may need special tooling or slower speeds, and our engineers will tell you which ones are worth the cost and which are not.

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  Rough, relieve, finishSeparate the heavy removal from the sizing passes.
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  Light finish cuts0.2–0.5 mm radial engagement keeps walls stable.
• 3
  Cut symmetricallyBalanced removal on both faces limits bowing.

Aerospace buyers want evidence, not a verbal assurance. Our inspection flow starts with a raw material check against the mill certificate, continues with in-process monitoring at defined intervals, and ends with a final inspection before shipment. Reports are available on request.

For critical features we use CMM programming against the datum scheme on the drawing, plus surface and hardness checks where the specification calls for them. If a feature cannot be measured after assembly, we measure it in-process and record the values.

Every part ships with 100% inspection before shipment, and our recorded qualification rate is 99.99%. Traceability runs from the material lot through the machine, the operator and the inspection record. Uploads stay secure and confidential, and an NDA is available on request.

The facility holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The information security certificate matters more than people expect on defense-adjacent work, because it covers how drawings and CAD files are handled, not just how parts are cut.

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  Material firstMill certificates checked against the specification.
• 2
  Measure to the datumCMM programs follow the drawing datum scheme.
• 3
  Document the lotMaterial, machine, operator and inspection records link up.