China Aluminium CNC Milling Machining Service Factory

The alloy decides how the part cuts, how it finishes, and whether it survives service. 6061-T6 is the default for brackets, housings and fixtures because it machines cleanly and welds and anodizes predictably. 7075 offers roughly twice the yield strength of 6061, so it suits loaded airframe and racing parts, but it costs more and annoys cutters with chip packing on deep pockets.

2024 machines to a fine finish and holds tight bores, though its copper content makes it less corrosion-resistant unless it gets a protective coating. 5052 and 5083 bend and weld well, which is why sheet-metal style parts and marine housings often start there. 6082 sits close to 6061 with slightly better strength in Europe-specified drawings, and 6063 is chosen for extrusion-based parts.

Casting alloys such as ADC12 behave differently again. They can contain porosity, so a milled face may open a void that never appeared on the drawing. When we quote an ADC12 part, we plan the first cut depth and the fixture around that risk rather than after it.

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  6061-T6General purpose. Good anodizing, stable threads, low risk.
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  7075High strength. Sharper tooling and lighter radial cuts.
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  2024Tight bores, less corrosion resistance. Coat it.
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  5052 / 5083Formable and weldable. Common in enclosures and panels.

A three-axis mill handles a part with features on one face or on faces reachable by refixturing. That covers a large share of aluminium work: plates, heat sinks, manifolds with simple ports, and mounting brackets. Refixturing is not a flaw, but every extra setup adds a datum shift, so the tolerance stack grows.

Four-axis work adds a rotary table, usually Ø400 mm, which lets the spindle reach several sides without releasing the part. Long shafts, valve bodies and parts with a repeating pattern around a centerline fit here. Five-axis simultaneous machining goes further: undercuts, compound angles, deep pockets with drafted walls and organic ribs come off in one setup. With 16 simultaneous 5-axis centers on the floor, we route parts there when the geometry demands it, not as a default.

Size drives the decision too. Our largest travel is 4,000 × 400 × 150 mm, which suits long beams, rails and extrusion profiles. Medium work sits in the 750 × 1,150 × 550 mm and 600 × 600 × 600 mm envelopes, and compact precision parts run on 500 × 500 × 450 mm and 500 × 310 × 200 mm machines. Putting a 40 mm part on a large gantry machine wastes setup time and rarely improves the result.

Wall thickness matters more than size. Thin aluminium walls deflect under cutting force and chatter. Below about 0.8 mm on an unsupported wall, we ask for a redesign or accept a slower, more expensive process with a custom fixture.

General milling holds ±0.05 mm on aluminium without much effort. Our published capability is ±0.005 mm, and that number only applies to specific features: bored holes, ground faces, and dimensions measured on the machine that produced them. It is not a blanket tolerance across a 600 mm part. Engineers who need it should mark critical dimensions on the drawing instead of tightening the title block.

Surface finish follows the same logic. As-machined aluminium lands around Ra 1.6–3.2 μm. A finishing pass with the right cutter and coolant reaches Ra 0.8–1.6 μm, which is the usual target before anodizing. Below that, Ra 0.2–0.8 μm, the part normally needs lapping, polishing or precision grinding, and the cost steps up sharply.

Anodizing changes dimensions. A Type II clear coat adds roughly 5 to 10 μm per surface; hardcoat adds more and builds on corners. If a bore must stay within ±0.005 mm after coating, tell us before machining so we can leave stock or mask the feature. Masking threads and bores is normal, but it has to be planned at the CAM stage, not after the parts are anodized.

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  Mark critical dimsA blanket tight tolerance raises price on every feature.
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  Anodize stockLeave material for coating growth on fits and bores.
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  Deburr before coatingSharp edges coat thin and show bare metal.

Aluminium is soft and gummy, so the failure modes are different from steel. Built-up edge forms on the cutter when speeds are too low or the tool has too little rake, and it tears the surface instead of cutting it. Galling shows up on tapped holes and reamed bores. Both are avoided with sharp polished-flute tooling, high spindle speeds, generous coolant flow, and a feed rate that keeps the cutter engaged rather than rubbing.

Fixturing decides accuracy more often than the machine does. Aluminium moves when you clamp it. Vacuum plates, soft jaws machined to the part profile, and light clamping pressure with support underneath keep a thin plate flat. On a 3 mm plate, clamping force alone can bow the part several hundredths of a millimeter, then it springs back after unclamping and the flatness report looks wrong.

Chips are the other practical problem. Stringy aluminium swarf wraps around tools and blocks coolant. Through-spindle coolant and peck routines for deep pockets keep the cut clear. For parts with deep blind pockets, we often rough with a smaller cutter and a trochoidal path rather than a large tool that chatters at the bottom.

Every part we ship goes through 100% inspection, with a raw material check, in-process monitoring and a final inspection. Reports are available when the drawing calls for them, including dimensional reports and material certificates. If a part is safety-related or goes into a regulated assembly, ask for the report up front so it is built into the routing rather than added at the end.

Certifications are a filter, not a guarantee. GreatLight holds ISO 9001:2015, IATF 16949:2016 for automotive work, ISO 13485:2016 for medical devices, and ISO 27001:2022 for information security. The last one matters if you send CAD files and drawings: it covers how those files are stored and who can reach them. An NDA is available on request, and uploads are handled as confidential.

For a first order, the useful move is a small paid batch. Send one or two parts, ask for the inspection report, and check the anodized finish and thread condition yourself. A factory that cannot produce a clean dimensional report on two parts will not produce one on two thousand.