CNC Machining of Aluminum Alloys for Aviation Applications

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  Key takeaways
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  Choosing the alloy before CNC machining of aluminum alloys starts
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  How CNC machining of aluminum alloys holds thin walls flat
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  Which machine setup suits the part geometry
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  Tolerance, finish and inspection on aviation aluminum parts
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  Finishing and assembly steps after machining
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  When this process fits your program and when it does not
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  Alloy and setup selection for aviation aluminum parts

Aviation aluminum is not one material. The 2xxx and 7xxx families carry copper or zinc and reach high strength, but they machine and behave differently from 6061. 2024-T351 cuts clean and holds a thread well, yet it has poor corrosion resistance in bare form and is usually clad or coated. 7075-T6 is stronger still and common on fittings, but it is notch-sensitive and less weldable.

6061-T6 sits in a different place. It is weaker than 2024 or 7075, but it welds, anodizes predictably and resists stress-corrosion cracking. For non-flight-critical brackets, sensor housings and ground support hardware, that trade is usually worth taking. 5083 and 5052 are the weldable plate options where a formed or welded assembly is involved.

A practical rule: pick the alloy from the drawing's fatigue and corrosion notes first, then check whether the shop can hit the features in that alloy. A 0.8 mm wall in 7075-T6 is a different job from the same wall in 6061-T6. The stronger alloy cuts with less margin before it springs or chips.

We keep 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12 in the material list. If your drawing calls out a temper that is not stocked, say so early, because heat-treat lead time sits outside our machining window.

Thin ribs, webs and gussets move for three reasons: cutting force, clamping force and residual stress inside the plate. The cutter is usually the smallest of the three. A 3 mm rib that measures 3.02 mm on the bench after unclamping was pushed, not cut, to that number.

The sequence that works is rough, relieve, finish. Rough with a 10–12 mm carbide end mill at 0.3–0.5 mm radial engagement and leave 0.5 mm on the walls. Unclamp and let the part rest. Then finish with smaller stepovers and lower radial load, so the wall is cut close to its free state.

Spindle speed depends on the alloy and the tool. In 6061-T6, a 12 mm three-flute carbide tool runs comfortably at 8,000–12,000 rpm with 3,000–5,000 mm/min feed in a stable setup. In 7075-T6, drop the surface speed and keep the chip load up, or the edge will rub and work-harden the surface.

Coolant matters more than people expect. Aluminum conducts heat away quickly, so the tool edge stays hot while the part stays cool. Flood coolant or high-pressure through-spindle coolant keeps chips out of deep pockets. Dry cutting 7075 in a deep rib pocket tends to end in recut chips and a poor finish.

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  Rough and finish in separate setupsLeave 0.5 mm on walls, unclamp, then take the final pass.
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  Use vacuum or low-pressure fixturingClamping pressure moves thin plate more than cutting does.
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  Keep the tool path smoothConstant engagement beats full-width slotting in thin webs.
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  Check after unclamping, not duringIn-cut dimensions only tell you what the clamp is holding.

A bracket with features on four faces is cheaper on a 4-axis mill with a tombstone than on a 5-axis machine. The part stays in one setup, the operator indexes the rotary, and the cycle is easy to repeat. We run 12 four-axis mills for exactly this class of work.

5-axis simultaneous cutting earns its cost on contoured surfaces, angled bosses and deep pockets that would need three separate fixtures otherwise. We run 16 simultaneous 5-axis machining centers. Each setup removed is one less datum shift between operations, and datum shifts are where aviation parts usually lose their true position.

Size sets the machine too. The largest travel we can offer is 4,000 × 400 × 150 mm, which suits long stringers and spar sections. Medium work sits on 750 × 1,150 × 550 mm and 600 × 600 × 600 mm machines. Small precision parts go on 500 × 500 × 450 mm or 500 × 310 × 200 mm platforms, where the smaller envelope usually gives better thermal stability.

Turned features go to 16 mill-turn centers, with a Ø400 mm rotary table available. If a part mixes a turned bore with milled flats, mill-turn removes a second op and the concentricity error that comes with it.

We quote ±0.005 mm (±0.0002 in) where the drawing needs it, typically on bores, bearing seats and mating faces. That number is a capability, not a default. Applying it to every dimension on a 900 mm part drives probing time, temperature control and scrap risk, and the price reflects that.

Surface finish is specified the same way. As-machined faces land at Ra 1.6–3.2 μm. A finer pass reaches Ra 0.8–1.6 μm, and Ra 0.2–0.8 μm is available where a seal or a sliding fit requires it. Finer finish means slower passes and more tool changes, so it should be tied to a function on the drawing.

Inspection runs through the whole job, not just at the end. Raw material arrives with certificates and is checked against the drawing callout. In-process checks catch drift while the part is still in the machine. Final inspection is 100% before shipment, and reports are available on request with the lot.

Our plants hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. For aerospace work, the IATF and ISO 9001 systems carry the process control and traceability requirements that buyers typically audit.

Most aviation aluminum parts get a coating, and the coating changes dimensions. Type II clear anodize builds about 5–12 μm per surface. Type III hardcoat builds more and is harder, which matters on wear surfaces. If a bore has a press fit, the anodize thickness belongs in the model before the first cut.

Masking is the other decision. Threads, bearing bores and electrical bonding points are often masked so the coating does not change the fit or the conductivity. Conductive anodize is an option where the part needs both corrosion protection and a ground path.

Deburring and edge break come before coating, not after. A sharp edge under an anodized layer will still cut a glove, and it gives a stress riser on a fatigue part. Bead blasting and tumbling give a uniform matte surface that reads well on inspection.

Laser marking is available for part numbers and lot codes, with a minimum character height of 1.5 mm. Marking on a coated surface is more legible than marking under the coating, so we usually do it last.

CNC machining of aluminum alloys fits prototype and low-to-mid volume aviation work well. There is no minimum order quantity, so one bracket and a 10,000-part run both go through the same route. Quotation and free DFM analysis come back within 12 hours, and production can start within 24 hours of a released order.

Parts ship in 3–5 days for standard jobs. Our historical late-delivery probability is below 2%, which matters when a test fixture is holding up a build. That number is a record, not a promise, and long-lead material or a coating line can still move a date.

The process fits poorly when the geometry is a thin shell with compound curvature, or when the annual volume is high enough that a casting or forging pays for its tooling. A die-cast or forged blank that is then finish-machined is often the better route at volume.

It also fits poorly when the design has not settled. If the wall thickness is still moving between revisions, machining a plate now means paying again later. In that case, cut a prototype, test the load path, then commit to the production route.