Chinese Rapid Prototyping Experts: How to Judge Real Capability

Rapid prototyping in China covers more ground than 3D printing. A working enclosure, a load-bearing bracket and a fluid manifold are three different problems. Printing gets you geometry in a day, but the material properties are not the same as the final part. When a part will be tested under load, heat or vibration, the prototype usually needs to be machined from the same alloy as production.

CNC milling and turning remain the default for functional metal prototypes. On a 5-axis center, an angled boss or a contoured pocket is cut in one setup, so you avoid the stacked error that comes from three separate fixtures. GreatLight runs 16 simultaneous 5-axis machining centers alongside 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. That mix matters more than a single impressive machine, because most prototypes need two or three operations before they are finished.

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  Machined metal prototypeLoad-bearing parts, thin walls, tight bores, threads. Best when material must match production.
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  Vacuum castingSmall runs of polyurethane parts from a master pattern. Good for housings and covers.
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  Sheet metalEnclosures, brackets and chassis parts where bend radii and flatness drive the design.
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  Die castingThin-wall metal housings at higher volume, where tooling cost is justified.

Many suppliers quote ±0.001 mm on the front page. That number is not a shop-wide capability; it is what a grinder can hold on a small, rigid feature under ideal conditions. The claim becomes meaningless when the part is 300 mm long, the wall is 1.2 mm thick, or the material is 17-4PH that moves after heat treatment. Ask what the supplier can hold across the whole part, not on one feature.

GreatLight quotes ±0.005 mm (±0.0002 in) as a process tolerance. That figure is realistic for machined features on rigid parts, and it is the number we are prepared to inspect against. On long parts, thermal drift and workholding deflection grow with length, so we will tell you which dimensions need a second operation or an in-process check rather than promise a number we cannot repeat.

Repeatability is the harder question. A first article that measures well proves the setup was good on that day. What you want to know is whether the fifth part measures the same. Temperature-controlled areas, scheduled machine calibration and operators who own their own inspection data are what keep a process inside tolerance across a run.

Callout the critical dimensions on your drawing. Five tolerances that matter are easier to hold and easier to inspect than a general note that covers every surface.

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  Small rigid feature±0.005 mm is achievable and repeatable with the right fixture.
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  Long slender partExpect growth from thermal drift; plan a second operation or a stress relief step.
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  Thin wallBelow roughly 1 mm, deflection during cutting drives the result more than the machine.
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  After heat treatmentDistortion must be machined out; leave stock and finish after treatment.

Part size decides which machine your job lands on. GreatLight's largest travel is 4,000 × 400 × 150 mm, which suits long extrusions, rails and frame members. The medium group covers 750 × 1,150 × 550 mm and 600 × 600 × 600 mm, which is where most prototype fixtures and housings sit. Compact machines handle 500 × 500 × 450 mm and 500 × 310 × 200 mm, and a Ø400 mm rotary table covers round parts that need milling on the face and the diameter.

Across three wholly-owned plants covering 7,600 m², the shop runs 127 high-precision CNC machines. For a prototype program, the useful number is not the total count. It is how many machines can be freed for a short run without pushing a production order aside. That is why we keep prototype work on separate spindles from long production runs.

Materials are not a side note. Aluminium 6061, 7075 and ADC12 cover most brackets and housings. Stainless 303, 304, 316L and 17-4PH cover medical and food-contact parts. Titanium TC4 (Ti-6Al-4V), Inconel and magnesium AZ31B appear when weight or temperature demands it, and each one changes tool wear, cutting speed and lead time.

Plastics behave the same way. POM and PA machine cleanly and hold threads. PEEK needs sharp tooling and slower passes. Carbon fibre reinforced stock eats cutters, so we plan tool changes into the quote instead of discovering them mid-run.

A certificate on the wall says the management system was audited. It does not tell you whether your part passed. For prototypes, the useful evidence is dimensional data tied to your drawing: first article inspection, in-process checks at the operations that move material, and a final inspection before the parts are packed. GreatLight inspects 100% of parts before shipment and can send reports on request.

Raw material traceability is the second piece. If a prototype bracket fails a test, the first question is whether the alloy was what the drawing called for. Mill certificates and an incoming material check answer that. For medical and automotive programs, this record is often the difference between a prototype that can be used for a design review and one that cannot.

Surface finish belongs in the same conversation. A tolerance on a bore means little if the finish is rough enough to wear a mating shaft. We measure finish in Ra and machine to three bands: Ra 0.2–0.8 μm for sealing and sliding surfaces, Ra 0.8–1.6 μm for general functional fits, and Ra 1.6–3.2 μm as-machined where appearance and friction are not critical.

Ask for the inspection plan before the run starts. Adding a check after the parts are cut costs another cycle.

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  FAI reportKey dimensions measured against the drawing on the first part.
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  In-process checkTaken after operations that remove significant stock or change geometry.
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  Material certificateMill cert plus incoming check, matched to the alloy on the drawing.
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  Final reportMeasured values and finish bands recorded before packing.

Finishing is where prototype schedules slip most often. Anodizing, plating, powder coating and bead blasting are separate operations, and each one adds handling. A shop that controls finishing in-house keeps the parts on one route and one inspection record. GreatLight offers clear, colour, hardcoat and conductive anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing, polishing, and laser marking down to 1.5 mm character height.

Masking decisions belong on the drawing. If a bore must stay conductive while the body is anodized, the mask has to be planned before the parts go to the line. Adding it later means stripping and rework, which costs a cycle you did not budget for.

Compliance is narrower than a certificate count. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. For an automotive prototype, the IATF framework is what a tier-one supplier will ask about. For a medical device, ISO 13485 shapes how records are kept. ISO 27001 covers how your files are stored, which matters when the drawings are unreleased.

Match the certificate to the program, not to the logo on the website. A supplier with four certificates and no process control is a worse bet than one with two that are actually followed.

Uploads are held as confidential, and an NDA is available on request when your drawings are sensitive.