Swiss Machining Stainless Steel Parts

On our CITIZEN A16, we can start from Ø0.5 mm in stainless steel. In practice, the minimum is determined by feature complexity — a plain turned shaft at Ø0.5 mm is achievable, but a part with cross-drilled holes at Ø0.8 mm requires careful DFM review. Our engineers will tell you the practical limit for your specific geometry. Most stainless Swiss work we run falls in the Ø1–15 mm range.

We use aggressive, positive-rake cutting geometry to shear the material cleanly before the hardened layer builds up, maintain sharp tooling with scheduled change intervals, and apply high-pressure coolant directly to the cutting zone. For critical diameter features, we finish at a slow feed with a dedicated finishing insert rather than using the same insert for roughing and finishing. The guide bushing in a Swiss machine provides the rigidity that prevents deflection-induced tolerance loss — which is the other major failure mode in stainless turning.

316L is the standard choice for medical instrument parts — the molybdenum addition and low carbon content give it excellent corrosion resistance and compatibility with sterilization environments. For load-bearing parts that need higher strength (surgical pins, bone screws, certain implant tool components), 17-4PH in the H900 condition is common — it's machined in the annealed state and then aged after machining to reach hardness. Both grades are electropolished in our network to Ra ≤ 0.2 μm for sterility and visual inspection compliance.

Yes, passivation is a standard post-process we offer. We follow ASTM A967 — the most widely specified passivation standard for stainless steel. Both nitric acid and citric acid processes are available; citric acid is preferred for semiconductor and medical applications due to its lower environmental and safety burden. After passivation, parts are tested with a water break test and, on request, salt spray tested per ASTM B117. The passivation certificate is included in the shipment documentation.

Yes, we machine 17-4PH regularly. We machine it in the annealed (Condition A) state, which gives the best tool life and surface finish. After machining, precipitation hardening is performed by a certified heat treatment partner — H900, H925, H1025, or H1150 conditions depending on your strength and hardness requirements. The heat treatment certificate is included in the shipment documentation. Hardness is verified on finished parts with our Vickers hardness tester.

First article lead time is typically 10–15 working days for standard stainless grades (303, 304, 316L) and 15–25 days for 17-4PH or 440C, which require additional material sourcing and heat treatment coordination. After first article approval, production lead time depends on quantity — for typical runs of 1,000–50,000 pieces, we target 20–35 working days. Rush scheduling is available on a case-by-case basis — discuss at the quoting stage.

No — they're different processes that achieve different results, and both are sometimes used together. Passivation (ASTM A967) is a chemical treatment that removes free iron and restores the passive chromium oxide layer without changing the surface geometry. Electropolishing is an electrochemical machining process that removes a controlled layer of material (typically 10–30 μm), which improves surface finish, removes micro-asperities, and produces a bright appearance. Electropolishing inherently also passivates, but passivation alone does not improve surface finish. For UHP semiconductor or high-sterility medical parts, electropolishing is the preferred choice. For general corrosion protection, passivation alone is usually sufficient.

Yes. Under our IATF 16949:2016 certification, we can provide PPAP documentation up to Level 3, including: Part Submission Warrant (PSW), Design Records and Engineering Change documentation, Process Flow Diagrams, Control Plans, MSA (Measurement System Analysis), SPC data, and Initial Sample Inspection Report (ISIR). Discuss specific PPAP level requirements at the quoting stage so we can plan the documentation workload into the first article timeline.