China CNC Stainless Steel Service

The base is iron, with at least 10.5% chromium added. That chromium forms a thin passive oxide layer on the surface. Scratch it and the layer rebuilds itself in air. This is why the material resists corrosion without paint or plating. Chromium content also changes how the alloy cuts. A 304 part and a 303 part can share the same drawing dimensions and still machine very differently.

The four families you will see on drawings are austenitic (303, 304, 316, 316L), ferritic (430), martensitic (420, 431, 440C), and precipitation hardening (17-4PH, also written SUS630). Austenitic grades are the most common in machining. They work-harden quickly, gummy chips form at low feed rates, and heat builds up at the cutting edge instead of leaving with the chip. Martensitic grades cut more freely but are harder and respond to heat treatment.

Pick a grade from the part function, not from habit. A housing in a wash-down area usually needs 316L for its molybdenum content, which resists chlorides. A shaft that must be hardened and ground may be better in 17-4PH. A bracket that only needs moderate corrosion protection can run in 304 or 430 at lower cost. Adding molybdenum or nickel raises the price of the bar stock, so grade choice is also a cost decision.

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  303Free-machining austenitic grade with sulfur added. Best chip control, lowest tool wear, suitable for high-volume turned parts.
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  316LLow-carbon austenitic grade with molybdenum. Use where chlorides, salt spray, or cleaning chemicals are present.
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  17-4PHPrecipitation hardening grade. Machines in the annealed state, then reaches high strength after aging.

Machining stainless steel is a subtractive process like any other CNC work. A CAD model drives tool paths, and a rotating cutter removes material from bar stock or plate. The difference sits in the cutting zone. Stainless steel has lower thermal conductivity than aluminum, so heat stays near the edge. It also work-hardens, meaning the surface gets harder as the tool rubs it. Both effects shorten tool life and can push dimensions out of tolerance if the shop runs the same parameters it uses on aluminum.

Feed and speed have to be set so the tool cuts under the hardened layer instead of rubbing on it. A cut that is too light is worse than one that is too heavy. Carbide grades with a tough substrate and a coating such as AlTiN hold up better than general-purpose inserts. Coolant has to reach the edge at high pressure, because a starved cut on 316L will chip the insert within minutes.

Thin walls and long slender parts are the usual trouble spots. Stress released from the bar stock moves the part while it is still being cut. Shops that handle this well rough the part, let it rest, then take a light finishing pass. On our 16 simultaneous 5-axis machining centers, we can reach features from several directions in one setup, which reduces the number of times a part is unclamped and re-datumed.

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  Rigidity firstShort tool overhang and a solid workholding setup matter more here than on softer metals.
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  Heat controlHigh-pressure coolant and correct surface speed keep the edge alive and hold size.
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  Stress reliefRough, rest, then finish on thin-wall or tight-tolerance parts.

We hold ±0.005 mm (±0.0002 in) on stainless steel where the drawing calls for it, and 100% of parts are inspected before shipment. That number applies to features the process can actually control. A bore position driven by a single setup behaves differently from a stack of tolerances across five operations. Send the drawing and we will tell you which callouts are achievable as drawn and which ones need a note.

Surface finish depends on the operation. Fine turning or grinding gets you Ra 0.2–0.8 μm. A good milled or turned surface sits at Ra 0.8–1.6 μm. As-machined work is normally Ra 1.6–3.2 μm. Stainless steel tends to smear rather than shear, so a surface that looks bright may hide a torn layer underneath. If the part needs a sealing face or a bearing fit, specify the finish and the inspection method together.

Post-processing changes dimensions slightly. Electropolishing removes a few microns from every exposed surface. Bead blasting can round a sharp edge. If a tolerance is tight and the part is also plated or polished, tell us the finish sequence so we can leave material for it. We offer anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing, polishing, and laser marking with a minimum character height of 1.5 mm.

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  Tight calloutsFlag the features that matter. Blanket tolerances drive cost without adding function.
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  Finish plus toleranceFinishing removes material. Sequence it before the final size is locked.

GreatLight has run stainless steel parts since 2011 from three wholly-owned plants in Dongguan and Singapore, covering 7,600 m² with 150 technicians and 127 high-precision CNC machines. The equipment list includes 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. Maximum processing size is 4,000 mm, with a Ø400 mm rotary table for round work.

The practical questions are the same whether you buy locally or overseas. Can the shop quote from a STEP file and flag design-for-machining issues? Do they tell you which grade they will actually buy? Can they inspect and document it? We return a quotation and a free DFM analysis within 12 hours, production can start within 24 hours, and parts ship in 3–5 days. There is no minimum order quantity, so a single prototype and a 10,000+ part run go through the same process.

Certifications matter when your customer asks for them. We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. Inspection covers raw material check, in-process monitoring, and final inspection, with reports on request. Uploads are kept secure and confidential, and an NDA is available on request.

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  DFM feedbackQuotation and free DFM analysis within 12 hours of receiving your files.
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  No MOQOne prototype or 10,000+ parts, same workflow.
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  DocumentationMaterial and inspection reports on request.