China CNC Plastic Machining Services Factory

Polymer chips do not curl off the tool. They soften, smear, and weld themselves back onto the cutter if the heat is not carried away. That is the single biggest difference between cutting aluminum and cutting ABS or HDPE. A feed and speed recipe that looks conservative for 6061 will melt a 10 mm POM pocket in seconds.

Thermal expansion runs the other way too. Plastics move five to ten times more per degree than steel. A part machined at 28 °C and measured at 20 °C on a CMM can show a size shift that has nothing to do with the machine. We hold finished parts in the inspection room long enough for temperature to settle before final measurement, and we cut to a target that accounts for the material's coefficient.

Rigidity is the other constraint. Glass-filled PA or carbon fibre sheet will hold a wall, but unfilled PP and LDPE deflect under clamping force before the tool even touches them. Those parts need light passes and support, not brute force.

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  Heat is the failure modeSharp, polished flutes and high rake angles evacuate chips before they re-melt.
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  Clamping marks are permanentSoft jaws and vacuum chucks spread the load so thin walls do not take a set.
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  Measure at temperatureA 100 mm PEEK part can grow 0.05 mm between a cold shop and a warm CMM room.

The choice is driven by three questions: what load it carries, what temperature it sees, and whether it touches chemicals or skin. Get those answers and the shortlist is usually two or three grades. We machine ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre, and we will tell you when a grade is a bad fit rather than quote it anyway.

POM is the default for sliding and wear parts. It holds tolerance, machines clean, and has low friction. It does not like strong acids and it will not survive a 120 °C service temperature. PC is the pick when you need impact strength and optical clarity, but it stress-cracks around sharp internal corners, so radii matter. PEEK takes heat and chemicals that destroy everything else on this list. It also costs more per kilogram than most metals and it is abrasive on tooling, so the design should not add features you do not need.

For prototypes, the material and the production material should match if wear or chemical exposure is part of the test. A PP prototype that validates in a jig tells you very little about how the same geometry behaves in PEEK.

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  POMGears, bushings, sliding blocks. Tight tolerance, low friction, moderate heat.
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  PCHousings, lenses, guards. High impact, needs generous corner radii.
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  PEEKAerospace and medical parts at high temperature. Expensive, abrasive, worth it.
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  PA and carbon fibreStructural brackets. Stiff, but moisture uptake changes dimensions.

The clamp is where most plastic jobs go wrong. A steel vise jaw will crush a 2 mm PC wall and leave a witness mark that no finishing step removes. We cut custom soft jaws from POM or aluminum for repeat parts, and for thin-wall geometry we use vacuum chucks or dedicated fixtures that spread the load across a face rather than a point.

Tooling follows the same logic. Single-flute and two-flute end mills with polished flutes and high rake angles clear soft chips fast. Diamond or PCD tooling is reserved for abrasive filled grades and for PEEK and carbon fibre, where carbide wears out mid-run and the size drifts with it. Coolant is usually air or a light mist. Flood coolant on unfilled plastics can cause thermal shock and leave a cloudy surface.

For parts that need two setups, we plan the datum before the first cut. A plastic part that is flipped without a machined reference face will not come back to position, because the material moves slightly once the first side is relieved.

We work to ±0.005 mm on metal parts, and we can hit that on rigid filled plastics under good conditions. On unfilled POM, PC or PP, the material itself sets the limit. A 100 mm unfilled PP part will move more than ±0.005 mm from moisture and temperature alone, no matter how good the machine is. Quoting that tolerance would be dishonest.

A practical rule: tight tolerances belong on the features that mate with something. Put ±0.05 mm on a bearing bore and leave the outer profile at ±0.2 mm. That reduces cost and reduces the chance of a rejected batch. We mark which dimensions are functional during DFM review and say so when a callout is tighter than the material supports.

Surface finish runs from Ra 0.2–0.8 μm on a fine cut to Ra 1.6–3.2 μm as machined. A polished finish on plastic is achievable, but it is a separate operation and it can round a sharp edge. If the edge matters, say so on the drawing.

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  Functional dimensionsHold these tight. Bores, mating faces, hole centers.
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  Cosmetic dimensionsOpen these up. Outer profiles, non-contact walls.
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  Edge conditionA polished surface and a sharp edge cannot both be guaranteed.

Ask what they machine most of. A shop that runs aluminum all day will struggle with your PEEK manifold, because the tooling, coolant and inspection habits are different. Plastic-specific tooling, soft jaws and a temperature-controlled inspection room are the signs to look for.

Then ask how they inspect. Plastic parts are often rejected for dimensions that were never critical, while a real issue like a stress crack at a corner goes unnoticed. A supplier that reviews the drawing with you before cutting, and flags a bad tolerance callout, is worth more than one that quotes the lowest number and cuts exactly what you sent.

Finally, ask about documentation. Certifications, material certificates and inspection reports should be available on request. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022, and we inspect 100% of parts before shipment. Our uploads are secure and confidential, and we sign an NDA when a program needs one.

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  Plastic-specific toolingPolished single-flute cutters, PCD for filled grades, soft jaws in stock.
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  DFM feedback before cuttingA written note on tolerance, wall thickness and radii within 12 hours.
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  Documentation on requestMaterial certs and inspection reports, not a verbal assurance.

You send a STEP file and a drawing. Within 12 hours you get a quotation and a DFM analysis covering material, tolerances, wall thickness and any feature that will not cut cleanly. If something needs to change, we say so before the quote, not after the first article.

Production can start within 24 hours of approval. Parts ship in 3–5 days for most plastic jobs, and we run from a single prototype to 10,000+ part runs with no minimum order quantity. Three wholly-owned plants, 127 high-precision CNC machines and 150 technicians handle the load across Dongguan and our Singapore facility.

Every order goes through raw material check, in-process monitoring and final inspection. For plastic parts we add a temperature settle before the last measurement, because a part measured hot is a part measured wrong.