Aviation CNC machining expert: what that actually means on the shop floor

A general machine shop holds ±0.05 mm and calls it tight. Aviation work starts an order of magnitude finer. GreatLight machines to ±0.005 mm, which is ±0.0002 in. At that scale the machine is rarely the limiting factor. The fixture, the thermal state of the part, and the order of operations decide whether the number holds on the last cut.

Material changes the whole plan. Aluminum 6061-T6 and 7075 cut fast and stay put. Ti-6Al-4V (TC4) and Inconel generate heat in the cut zone instead of the chip, so tool life drops and the surface can work-harden if the feed is too light. Magnesium AZ31B cuts easily but demands chip control because fine magnesium swarf ignites. Each of these needs its own speeds, feeds and coolant strategy, not one generic program.

Traceability is the other split. A bracket for ground equipment can ship with a dimensional report. A flight part usually needs raw material certs, a process route, inspection records and a first article report. We build that paperwork alongside the chips, not after the fact. When a part fails a check, the record tells you which operation drifted.

• 1
  ToleranceAviation parts commonly land at ±0.005 mm; general work sits near ±0.05 mm.
• 2
  MaterialTitanium and Inconel need heat-aware cutting data, not aluminum recipes.
• 3
  EvidenceMaterial certs, in-process checks and final reports shipped with the parts.

Five-axis means the tool and the part move together on five axes at once: X, Y, Z plus two rotary axes. The payoff is not speed. It is that a complex contour, a pocket floor and a bolt-hole pattern can come off in one setup. Every extra setup adds a re-fixturing error and a new datum stack. Removing setups removes error sources.

For aerodynamic surfaces and turbine hardware, the tool can stay normal to the surface through the pass. That keeps the effective cutting radius constant, which holds surface finish (Ra 0.8–1.6 μm on a machined profile) and avoids the witness lines a three-axis raster leaves on a curved face. On thin-wall parts, the same motion lets us approach at an angle so the cutter pushes into the wall instead of lifting it.

GreatLight runs 16 simultaneous five-axis machining centers, with a Ø400 mm rotary table and travels up to 4,000 × 400 × 150 mm. Larger prismatic parts go on the 4,000 mm capacity machines. Five-axis is not automatic for every job. A simple flat plate with holes is faster and cheaper on a three-axis mill, and we will say so.

The cost of five-axis is programming time and a stiffer setup. When a part has one sculpted face and ten flat features, the honest answer may be a hybrid: five-axis for the contour, three-axis for the drilling. We quote the routing that holds the print, not the one that sounds most advanced.

• 1
  Good fitSculpted contours, thin walls, angled hole patterns, one-setup datums.
• 2
  Poor fitFlat plates with simple holes; a three-axis mill is faster and cheaper.

On a thin airframe rib, the fixture is the process. Clamp force bends a 2 mm wall before the cutter touches it. We use vacuum plates, low-melt fixturing or sacrificial tabs so the part is supported without being crushed. For parts that move after stress relief, we plan a semi-finish, a stress-relief cycle, then a finish pass that takes the last 0.2 mm.

Datum strategy matters as much as the machine. On a five-axis part we try to establish one primary datum and machine as many features from it as possible. When a print calls for a datum that only exists after a secondary operation, we flag it during DFM review instead of discovering it at inspection.

Tool selection follows the geometry. Long reach tools deflect, so we keep the length-to-diameter ratio as low as the pocket allows and use a smaller stepover on deep walls. For Inconel and titanium, high-pressure coolant and coated carbide keep the heat in the chip. We do not run a finishing pass on a work-hardened skin left by a dull tool.

Free DFM analysis comes back within 12 hours with the quote. If a radius is too small for the tool that reaches the floor, or a tolerance is tighter than the feature needs, that is where we say it. Fixing it in the model is cheaper than scrapping a titanium part.

A ±0.005 mm callout is a claim until it is measured. We inspect 100% of parts before shipment and keep three checkpoints: incoming raw material, in-process monitoring, and a final inspection. Reports are available on request. For first articles, the report maps each checked feature back to the drawing.

In-process checks catch drift early. If a boring tool wears and the bore grows, the operator sees it at the next check, not after the run. That is why a 99.99% qualification rate is a process result, not a promise about any single part.

CMM work needs a stable thermal state. A titanium part pulled hot from the machine reads differently from one that has settled. We let parts rest before final measurement on tight features, and we record the temperature when it matters. This is the part of aviation work that does not show up on a quote but shows up in the yield.

Surface finish is checked against the callout: Ra 0.2–0.8 μm for fine finishes, Ra 0.8–1.6 μm for high-finish surfaces, Ra 1.6–3.2 μm as-machined. Finishing options include anodizing, electroless nickel, plating, powder coating, black oxide, bead blasting, brushing and laser marking with a minimum character height of 1.5 mm.

Aviation work needs a machine mix, not one big machine. GreatLight runs 127 high-precision CNC machines across three plants in 7,600 m²: 16 five-axis centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. The mix lets us route a part to the machine that holds it best instead of forcing every job onto the most expensive spindle.

Size range matters too. Travels cover 4,000 × 400 × 150 mm for long parts, 750 × 1,150 × 550 mm and 600 × 600 × 600 mm for mid-size housings, and compact envelopes down to 500 × 310 × 200 mm for small precision details.

Quality systems hold the process in place. GreatLight is certified to ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The information-security cert matters when a customer sends controlled drawings. Uploads are handled as confidential, and an NDA is available on request.

Volume runs from one prototype to 10,000+ parts with no minimum order quantity. Production can start within 24 hours of a released order, and parts typically ship in 3–5 days. Historical late-delivery probability is below 2%.