China CNC Aluminum: Alloy Choice, Tolerances and Real Lead Times

Most aluminum parts we machine fall into three groups: general-purpose 6061, high-strength 7075, and the 2024 / 5052 / 5083 family used for sheet, marine and aerospace work. When a drawing says only "aluminum," we quote 6061-T6 by default. It welds, anodizes cleanly, holds a thread, and costs less than 7075 at the same volume.

7075-T6 is roughly twice the strength of 6061 and machines to a sharper edge, but it is harder on tooling and it does not anodize to the same even color. Use it for brackets, linkage arms and anything that sees real load. For housings and covers, the extra strength buys you nothing except a higher price and longer cycle time.

Some grades are best left to specific processes. 2024 machines well but corrodes quickly without protection, so plan an anodize or alodine step. 5052 and 5083 bend and weld better than 6061, which makes them the usual pick for sheet metal chassis. ADC12 is a die-casting alloy; it pours well and machines poorly, so keep it out of CNC-only designs.

Two more numbers matter. Hardness decides how thin a wall you can hold: below 1.0 mm on 6061, chatter and deflection start to show up on unsupported sections. Thermal expansion decides how tight a tolerance is realistic on a long part. Over 300 mm, aluminum grows about 0.023 mm per 1 °C, so a warm shop floor eats your tolerance before the tool touches the part.

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  6061-T6Default choice. General parts, housings, fixtures.
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  7075-T6High load. Brackets, arms, wear surfaces.
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  2024Aerospace. Needs corrosion protection.
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  5052 / 5083Sheet, welded frames, marine.

We run 127 high-precision CNC machines across three wholly-owned plants in Dongguan and Singapore. For aluminum that breaks down into 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. The mix matters more than the total. A part with features on five faces goes on a 5-axis center and comes off in one setup; the same part on a 3-axis machine needs three or four fixtures, and each refixture adds error.

Our standard machining tolerance is ±0.005 mm (±0.0002 in) on features we can reach and measure. That is not a blanket promise for every dimension on every drawing. It applies to bores, pockets and datums that are cut in the same setup and checked on the machine. A tolerance across two setups, or across a part longer than 300 mm, needs a conversation before we quote.

Size range runs from small sensor housings up to 4,000 mm. The large travel is 4,000 × 400 × 150 mm; medium machines cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm; compact machines handle 500 × 500 × 450 mm and 500 × 310 × 200 mm. We also run a Ø400 mm rotary table for parts that need continuous rotation rather than indexing.

Five-axis is not automatically the right answer. On a simple plate with holes on one face, a 3-axis machine is faster and cheaper, and the tolerance is just as good. The case for 5-axis is geometry you cannot reach otherwise: undercut pockets, compound angles, contoured surfaces, or a part where one setup removes four sources of stack-up error.

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  16Simultaneous 5-axis machining centers
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  ±0.005 mmStandard tolerance on reachable features
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  4,000 mmMaximum processing size
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  Ø400 mmRotary table for continuous work

Aluminum takes almost every finish we offer. Clear and colored anodizing, hardcoat, conductive anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing are all standard. Laser marking and engraving run down to a minimum character height of 1.5 mm.

Anodizing is the one that surprises people. Type II clear builds roughly 5–15 μm per surface and hardcoat goes thicker, so a tight bore can close up. If a bore carries a bearing or a mating pin, tell us it is a masked area. We mask it, or we cut it undersize before coating. Both work; guessing does not.

As-machined aluminum sits around Ra 1.6–3.2 μm. Bead blasting evens that out and hides tool paths, which is why it is common on visible covers. Where you need a sealing face or a sliding surface, we can hold Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm on the right geometry.

Cosmetic parts need a different conversation than functional ones. Color anodizing varies slightly batch to batch, and the same alloy from two suppliers can read differently after coating. If two housings must match side by side, machine them from one heat of material and finish them in one batch.

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  Mask before anodizeFlag bearing bores and mating faces on the drawing.
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  Ra 1.6–3.2 μmStandard as-machined surface.
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  Ra 0.2–0.8 μmFine finish, geometry dependent.
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  1.5 mmMinimum laser-marked character height

Ask what will be inspected, not just whether inspection happens. Our flow is a raw material check, in-process monitoring and a final inspection, with 100% inspection before shipment and reports on request. On aluminum, the usual failure modes are burrs in cross-holes, thread depth, and a wall that thinned because the stock was not square. Those show up in final inspection, but they are cheaper to catch in process.

Certifications are worth checking against your industry. We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. Automotive programs lean on the IATF scope; medical work leans on ISO 13485; the ISO 27001 certificate covers how customer files are handled, which is the one procurement teams forget to ask about.

Timing is usually simpler than buyers expect. Quotation and a free DFM analysis come back within 12 hours, production can start within 24 hours of a released order, and parts ship in 3–5 days. There is no minimum order quantity, so a single prototype and a 10,000-part run go through the same shop. Historical late-delivery probability sits below 2%.

Confidentiality is covered without asking. Uploads are secure and confidential, and an NDA is available on request. If your program needs one signed before files move, say so at the first message and we will handle it before the drawing is opened.

One practical note on cost. Aluminum pricing tracks the London Metal Exchange plus a conversion charge, so quotes are time-sensitive. A quote held for three months is a guess. If a program is still in review, tell us the expected release window and we will flag it when you are ready to commit.

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  12 hoursQuote and free DFM analysis
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  3–5 daysTypical shipping window after production
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  No MOQOne prototype to 10,000+ parts
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  NDA on requestSigned before files are opened