Aluminum CNC Machining: What Should You Confirm Before Sending a RFQ to a Chinese Shop?

Aluminum is the default material for lightweight, thermally demanding parts — and most of the world's aluminum CNC capacity sits in Shenzhen. If you are a buyer in the US, Germany or anywhere with tight delivery windows, here are the questions worth asking before you send the drawing, not after the first article arrives.

Q: Which aluminum alloys should I expect a shop to stock?

A: 6061-T6 and 7075-T651 are the workhorses and should be in stock in plate and bar. 6061 wins on corrosion resistance, weldability and cost; 7075 wins on strength-to-weight for structural and aerospace-adjacent parts. If a shop quotes 6061 for a 7075 drawing "as equivalent", push back — the fatigue and strength numbers are not equivalent. For housings and enclosures, ask specifically about 6061 plate flatness: stress-relieved plate saves an entire re-machining operation.

Q: What tolerance is realistic for aluminum in volume?

A: On CNC-milled aluminum, ±0.005 mm is our standard production tolerance — held with in-process inspection, not just promised on a quote — and critical features can go better where the drawing requires it. But holding it across a 10,000-piece run is a process question, not a machine brochure question. Ask how the shop compensates for thermal growth during long runs and how often in-process inspection samples a part. An honest answer mentions control charts; a vague answer mentions "high precision machines".

Q: Why does gang-type lathe capacity matter for aluminum turned parts?

A: Aluminum small parts — spacers, bushings, fittings, connector bodies — run fastest on gang-type CNC lathes, where tool changes take fractions of a second and the short tool overhang keeps size stable. A shop with dozens of gang-type cells can quote you a lower per-piece price simply because its machines spend more time cutting and less time indexing. When you evaluate a supplier for volume turned parts, the ratio of gang-type/Swiss-type cells to general-purpose lathes tells you more than the total machine count.

Q: What about surface finish — anodize, alodine, or as-machined?

A: Type II anodizing (clear or black) is the standard for housings; Type III hard anodize adds wear life but costs dimension — anodize grows roughly half its thickness outward, so critical bores must be pre-compensated. Confirm the shop treats anodizing as a dimensioned process, not a cosmetic afterthought. For EMI-critical housings, chromate conversion (Alodine/chem-film) preserves conductivity where anodize insulates.

Q: What minimum order and lead time should I expect?

A: A serious shop will accept a 1-piece prototype and 3-7 day sampling, then move to 7-15 day production runs — and for aluminum turned parts in the millions per month, price breaks come from bar-stock yield and cycle time, not from skipping inspection. If a quote is dramatically cheaper because it "skips FAI", the savings will be paid back in the first rejected shipment.

If you are comparing quotes on an aluminum part, send the drawing to mc@chxmetal.com — a one-page process review (stock size, fixturing, anodize stack-up) usually settles which quote is real. More on machining capability is at chxmetal.com, and the aluminum parts deep-dive is at CNC aluminum parts.