China CNC Metal Machining Service Factory

A China CNC metal machining service factory is usually judged on its machine list first, and that is fair. A part with features on five faces needs a machine that can reach those faces without four re-fixtures. Each re-fixture adds setup error, and setup error is what eats a ±0.005 mm tolerance before the cutter ever touches metal.

GreatLight runs 127 high-precision CNC machines across 3 wholly-owned plants covering 7,600 m² in Dongguan. The count that matters for complex geometry is 16 simultaneous 5-axis machining centers. For turning-dominant parts with milled flats, 16 mill-turn centers cut the part in one program. There are also 12 four-axis mills, 27 three-axis machines, and a Ø400 mm rotary table for round work that has to index accurately.

Travel limits decide more quotes than price does. The largest envelope is 4,000 × 400 × 150 mm. Mid-size work fits 750 × 1,150 × 550 mm or 600 × 600 × 600 mm. Compact work runs on 500 × 500 × 450 mm or 500 × 310 × 200 mm machines. If your part is longer than 4,000 mm, we will say so on the first reply instead of after the setup.

Where 3-axis still wins: flat plates, pockets with one open face, drilled and tapped hole patterns, and anything with a datum you can hold in a vise. Putting simple parts on a 5-axis machine raises the hourly rate without improving the result.

• 1
  5-axis workContoured surfaces, undercuts, angled ports, features on multiple faces.
• 2
  Mill-turn workShafts and housings where turning and milling share one datum.
• 3
  3-axis workPlates, brackets, and hole patterns that sit in one orientation.

We hold ±0.005 mm (±0.0002 in) on metal parts. That figure is a capability, not a default. Applying it to every dimension on a drawing raises cost with no functional gain, because most dimensions on a real part are locating features or clearance holes. Mark the dimensions that control fit and function, and leave the rest at general tolerance.

Surface finish follows the same logic. As-machined surfaces sit around Ra 1.6–3.2 μm. A good machined finish is Ra 0.8–1.6 μm, which is achievable with sharp tooling and a finishing pass. Fine finish at Ra 0.2–0.8 μm is reserved for sealing faces, bearing bores, and sliding surfaces. Chasing Ra 0.2 μm on a cosmetic bracket mostly burns cycle time.

Deep pockets are the usual place where a tight tolerance fails. A tool with a long length-to-diameter ratio deflects, and no machine can compensate for a cutter that bends. If a pocket is 6× deeper than its width, expect us to ask about cutter access and whether the corner radii can be opened up.

Thin walls behave the same way. Below roughly 0.8 mm on aluminum and 1.0 mm on stainless, chatter and spring-back dominate. Sometimes the answer is a different process. Sometimes it is a fixture that supports the wall while it is cut. Both are worth discussing before the drawing is frozen.

Aluminum 6061-T6 is the default for prototypes and low-volume parts. It machines fast, holds tolerance, and takes anodizing well. 7075 gives higher strength for brackets and airframe-adjacent hardware, but it is less forgiving on thin sections and costs more per kilogram. 2024 behaves similarly and is common where fatigue life matters.

Stainless 303 is the free-machining grade and the sensible pick for shafts and fittings. 304 and 316L are tougher to cut, generate more heat, and need slower feeds. 316L is the choice for medical and marine parts because of corrosion resistance, not because it machines nicely. 17-4PH (SUS630) is used where you need strength plus corrosion resistance and can accept heat treatment.

Steel grades 1018, 1045, 4130, 4140, and 4340 cover most structural work. 4140 and 4340 are often specified pre-hardened, which means the cutter sees harder material and cycle time goes up. Tool steel comes up for molds and dies.

Titanium and nickel alloys are a different category. TC4 (Ti-6Al-4V) and Inconel cut slowly, wear tooling fast, and need rigid setups. Magnesium AZ31B and AZ91D machine quickly, but chip handling and fire safety drive the process plan. If your part is Inconel, expect the quote to reflect tool life, not just machine time.

Every lot gets 100% inspection before shipment. That is a raw material check, in-process monitoring during the run, and a final inspection before packing. Inspection reports are available on request, and for regulated programs we can align the report format with what your quality team already uses.

The four certifications we hold are ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. The first covers general quality management. IATF 16949 applies to automotive work. ISO 13485 covers medical device manufacturing. ISO 27001 covers information security, which matters when you are sending CAD files to a factory on another continent.

On the commercial side, there is no minimum order quantity. Runs go from one prototype to 10,000+ parts. Quotation and a free DFM analysis come back within 12 hours, and production can start within 24 hours of approval. Parts typically ship in 3–5 days. Historical late-delivery probability is below 2%.

Uploads are handled as confidential, and an NDA is available on request. If your program requires one before files move, say so in the first message and we will route it that way.