China Plastic CNC Processing Guide

Injection molding needs a steel tool and a few thousand parts to pay it back. CNC cutting needs a program and a block of stock. For bridge tooling, pilot runs or a design that is still moving, milling and turning a plastic billet is usually the shorter path from drawing to a part in your hand.

The trade-offs are real. Cycle time per part is higher, so unit cost stays flat instead of dropping with volume. Geometry is limited only by tool reach, not by draft angles and ejector pins. Undercuts, deep pockets and thin ribs that would need side actions in a mold are cut directly.

Plastic also pushes back in ways metal does not. It springs away from the cutter, it holds heat, and it moves after the vise is released. A shop that treats plastic like aluminum will hold a few tenths on one part and miss it on the next fifty.

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  Choose machining whenQuantity is under a few thousand, or the design is not frozen
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  Choose machining whenYou need tight flatness, bored bores or threaded features
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  Choose molding whenAnnual volume is high and geometry is stable
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  Hybrid approachCNC a prototype, then cut the mold from the approved geometry

Most plastic work in China runs through a small set of engineering grades. ABS is the default for housings and brackets because it machines cleanly and takes paint or vapor smoothing. PC is chosen for impact strength and optical clarity, but it is notch sensitive and builds internal stress, so roughing passes need to stay light.

POM is the shop favorite for anything sliding. It holds ±0.02 mm easily, has a low friction coefficient and machines with a crisp chip. PEEK and PA handle heat and chemical exposure, though PEEK costs many times more than POM per kilogram and dulls tooling faster. Carbon-fibre-filled grades add stiffness but are abrasive, so expect shorter tool life and a higher quoted rate.

Glass-filled and carbon-filled stock also changes the finish. The fibre pulls out at the cut edge and leaves a slightly rough surface that cannot be polished back to a smooth gloss. If a cosmetic face matters, keep filled grades away from it or plan for a secondary operation.

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  ABSGeneral housings, brackets, painted covers
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  PCImpact parts, lenses, guards, clear windows
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  POMBushings, gears, sliders, precision spacers
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  PEEK / PAHigh temperature, chemical exposure, wear surfaces

On a stable grade like POM or ABS, a well-fixtured job holds ±0.05 mm on a milled feature and ±0.02 mm on a bored hole without much argument. Pushing to ±0.005 mm is possible on specific features such as a bearing seat or a mating bore, but it is bought with extra inspection, slower feeds and sometimes a climate-controlled room. Quote the tight number only where it does something.

Wall thickness is the other hard limit. Below roughly 1.0 mm, plastic flexes away from the cutter and the cut becomes a rub. Thin floors chatter, and thin ribs deflect under clamp pressure. When a design calls for a 0.5 mm wall, vacuum casting or 3D printing usually gives a truer part than milling.

Heat is the quiet failure mode. Plastic conducts heat poorly, so the chip carries almost none of it away. A tool that would run dry in aluminum will smear and burn a plastic edge. Coolant, air blast or a slower spindle speed keeps the cut clean, and that decision shows up in the surface finish, not just the size.

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  General milling±0.05 mm on most features
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  Bored holes±0.02 mm with a rigid setup
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  Tight seat±0.005 mm on selected features only
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  Minimum wallAbout 1.0 mm for reliable milling

Soft jaws machined to the part profile, vacuum plates for thin panels, and light clamp pressure do more for plastic accuracy than a faster spindle. A vise tightened like it is holding steel will bow a plastic block, cut true, and spring back out of tolerance once released. We cut soft jaws for nearly every plastic job that repeats.

Five-axis work removes some of that risk. With 16 simultaneous 5-axis machining centers on the floor, we can reach five sides of a part in one setup and avoid re-clamping a delicate feature. Fewer setups means fewer chances to lose datum. The rotary table takes work up to Ø400 mm, and our largest travel reaches 4,000 × 400 × 150 mm for long plastic profiles.

Deburring is not cosmetic on plastic. A sharp edge on a PC guard becomes a crack starter, and a burr inside a fluid channel changes flow. We deburr by hand with controlled scrapers and fine abrasives, then clean the part so no swarf stays embedded in the surface. Bead blasting gives an even matte finish but rounds sharp corners, so we mask features that must stay crisp.

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  Soft jawsMachined to profile, protects surfaces
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  Vacuum platesThin panels and large flat parts
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  One-setup 5-axisFewer datum shifts on complex parts
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  DeburringManual edge work, then clean and inspect

Ask what machines they will run and what stock they keep. A shop that mills plastic on a machine set up for steel will fight chip evacuation and heat all day. We run 127 high-precision CNC machines across three wholly-owned plants covering 7,600 m², with 150 technicians, and we keep common engineering grades in stock so a job does not wait on material.

Ask how they inspect a plastic part. Calipers are not enough on a flexible material. We check incoming stock, monitor in-process, and inspect 100% before shipment, with reports on request. A first article report on the critical features should come back with the parts, not three weeks later.

Ask about confidentiality and paperwork. Drawings leave your building, so get an NDA in place before you release them. Uploads are handled as confidential and an NDA is available on request. Certifications matter too: ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 cover quality, automotive, medical and information security. Match the certificate to your industry, not to the brochure.

Finally, test them with one part. A prototype order tells you more about communication and finish quality than any capability list. We quote and return DFM feedback within 12 hours, start production within 24 hours, and ship parts in 3–5 days.

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  Machine fitPlastic-dedicated spindles, dust and chip control
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  Inspection100% before shipment, reports on request
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  PaperworkNDA before drawings are released
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  Industry certIATF for auto, ISO 13485 for medical