CNC machining in China

China leads; alternatives compete. China supplied 6.8% of US imports of HS 8487.90 machinery parts in 2025 (UN Comtrade), behind Mexico at 24.1%, though it leads steel and aluminum article proxies.

Is China still the default source for CNC machined parts?

CNC machining (Computer Numerical Control machining) is the process of cutting a part out of a solid block, bar or casting with cutting tools whose paths are set by a computer program. China is still a large source of custom CNC machined parts, especially low-volume, quick-turn and mixed-process work, but it is not the default source for US buyers in the trade data that comes closest to measuring machined parts.

That qualification matters because no HS code (Harmonized System code, the international product classification used by customs) isolates "machined parts." Most machined parts are classified by their end use: a machined pump housing is a pump part, a machined bracket may be a vehicle part. Trade analysts therefore use a proxy, meaning a code that captures part of the category and stands in for the whole. The narrowest proxy is HS 8487.90, machinery parts not elsewhere specified ("nesoi"). In 2025 US imports under that code were US$442 million, and the supplier ranking was Mexico 24.1%, Germany 17.1%, Canada 12.4% and China 6.8%, according to UN Comtrade. China's share in 2018 was 11.5%.

Two broader proxies tell a different part of the story. In HS 7326.90 (other articles of iron or steel, where many machined and fabricated steel parts land), China supplied 28.1% of US imports in 2025, down from 40.8% in 2018. In HS 7616.99 (other articles of aluminum, including machined aluminum parts nesoi), China supplied 24.1%, down from 43.1%, with Mexico close behind at 21.6%. China still leads in both, but its lead is about half of what it was in 2018.

Hence the verdict: China leads some segments, and alternatives compete. A buyer's own HTS line (the 10-digit US tariff classification) decides both the duty and which statistic applies.

How CNC machining works and what drives the quote

CNC machining is a subtractive process: material is removed until the part remains. The main methods are distinct, and a single part often needs more than one.

• Milling uses a rotating cutter. Three-axis machines cut from above; 4-axis and 5-axis machines tilt the part or the spindle to reach complex surfaces in fewer setups.
• Turning rotates the part against a fixed tool on a lathe. Swiss-type lathes hold small, long parts close to the cutting point for precision.
• EDM (electrical discharge machining, by wire or sinker electrode) erodes hardened steel and produces sharp internal corners a cutter cannot reach.
• Grinding produces fine finishes and tight dimensions on hardened surfaces.

A CAM program (Computer-Aided Manufacturing software that converts the CAD model into tool paths, usually output as G-code) drives each machine. The quote follows from a short list of drivers: the number of setups (each time the part is re-fixtured), cycle time, material, tolerances, finishing such as anodizing, plating, passivation or heat treatment, and inspection.

CNC machining carries little hard tooling compared with molding or casting. The one-time costs are mostly fixtures (custom workholding) and programming, often called NRE (non-recurring engineering) and amortized across the order quantity, which is why piece price falls steeply with volume. Ownership questions therefore shift from a mold to the CAM programs and fixtures. A purchase agreement should state in writing whether the buyer owns them and may take them to another shop.

The work runs from RFQ (request for quotation) and DFM review (design for manufacturability) through material sourcing, programming and fixture build, first-article approval, production, finishing and inspection. Finishing is often subcontracted to a separate plating or anodizing shop, which adds transit and queue time; no official source gives stage durations, so none are stated here.

Tolerances, drawings and quality documents

Most disputes over machined parts trace back to the drawing. Dimensions without a stated tolerance fall back on a general-tolerance standard such as ISO 2768, which has classes f, m, c and v from fine to very coarse. If the drawing does not name the class, the supplier effectively chooses it. Fits are specified under ISO 286 or ANSI limits, and form and position controls under ASME Y14.5 GD&T (Geometric Dimensioning and Tolerancing). The opposite error is as costly: tightening every feature slows machining and multiplies inspection.

The documents a buyer can request are standard across the industry:

• FAI (First Article Inspection), a full dimensional report on the first parts; aerospace work uses the SAE AS9102 format.
• CMM report from a Coordinate Measuring Machine, a probe that measures 3D geometry against the CAD model.
• Mill certificates showing alloy, heat number, chemistry and mechanical properties. Ask for the original mill certificate, not a certificate typed by the supplier.
• Finishing certificates covering anodize or plating thickness and salt-spray results, plus RoHS and REACH declarations where they apply.
• PPAP (Production Part Approval Process) for automotive programs.

For metal parts there is now a tariff reason for good paperwork. Section 232 rates turn on where the steel was melted and poured or the aluminum smelted and cast: Proclamation 11021 sets a 10% rate for articles made of US metal and a 200% rate for Russian aluminum. A mill certificate with a traceable heat number is how that origin is shown.

Tariff exposure as of October 2026

The duty on a machined part from China depends first on whether it is metal. Since 6 April 2026, Proclamation 11021 (91 FR 18201) applies Section 232 duty to the full customs value of listed steel, aluminum and copper articles, regardless of metal content. Before that date many derivatives were assessed on metal content only, so machining labor in China is now dutiable too. Annex I-A is the proclamation's list of goods at the 50% rate; Annex I-B carries 25%.

Four further points decide the stack on a given entry.

• Section 232 and the forced-labor duty do not stack. The forced-labor Section 301 action (FR Doc. 2026-15181) exempts articles under the Section 232 metals headings, so a listed aluminum part pays Section 232 and not the 12.5%. A plastic part pays the 12.5%. A court challenge to the forced-labor action has been reported in secondary sources; its status should be checked before entry.
• The older China Section 301 list duties generally apply in addition to Section 232, because the HTSUS chapter 99 notes say other duties are imposed in addition. Whether a particular machined-part code is on List 1, 2, 3 or 4A has not been verified here and must be checked line by line.
• The low-metal exemption is narrow. Annex goods outside chapters 72, 73, 74 and 76 with under 15% metal by weight report under 9903.82.03 at 0% (CBP CSMS #68253075, 3 April 2026). A chapter 73 or 76 article cannot use it.
• The IEEPA duties are gone. The Supreme Court held on 20 February 2026 that IEEPA does not authorize tariffs (Learning Resources, Inc. v. Trump, No. 24-1287).

A separate Section 232 investigation of robotics and industrial machinery ended with a proclamation on 28 October 2026 that imposes no tariffs yet and directs negotiations, with an update due within 180 days. It names no products. A licensed customs broker should confirm the classification and stack for each part.

Design exposure when the RFQ is the whole design

A CNC quotation normally requires the full 3D model and the drawing, which is the complete design. USTR's 2026 Special 301 Report keeps China on the Priority Watch List, lists trade secrets among long-standing concerns, notes high thresholds for criminal trade-secret cases in China, and cites NCSC reporting of enforcement gaps "particularly in China and Russia." The same report names Vietnam a Priority Foreign Country, its most serious category, so moving machining to Vietnam does not remove the exposure.

The common mitigations are structural rather than legal guarantees. Buyers split a design across suppliers, remove non-essential features from RFQ models, register trademarks and designs with CNIPA (China's National Intellectual Property Administration) before sharing files, and send drawings only after an NNN-style agreement (non-disclosure, non-use, non-circumvention) written under Chinese law. How such agreements are enforced in Chinese courts is outside the research behind this page.

Where machining for the US market is shifting

The trade proxies show where share moved between 2018 and 2025, not what any part costs.

• Mexico leads US imports of HS 8487.90 at 24.1% and ranks second in both HS 7326.90 (18.3%) and HS 7616.99 (21.6%).
• India doubled its share in HS 7326.90 (2.6% to 5.2%) and HS 8487.90 (1.9% to 3.9%).
• Vietnam remains small in these proxies: 0.8% of HS 8487.90 and 2.8% of HS 7326.90 in 2025.
• Germany and Italy hold a large share of precision machinery parts, at 17.1% and 5.1% of HS 8487.90.

Section 232 metals duties apply to every origin, with separate treatment for the UK, USMCA-qualifying goods and negotiated partners. Proclamation 11032 (effective 8 June 2026) gave some partners a 15% combined rate on certain chapter 84 and 87 codes; China stays at the 25% default. Moving a metal part out of China removes China-specific duties such as the Section 301 lists, not Section 232.

No official or academic source quantifies CNC job-shop capacity in Dongguan, Shenzhen or any other Chinese cluster; the only official description located is a 2002 USITC study of Guangdong tooling, too old to describe current capacity.

Common mistakes and how to evaluate a machine shop

The errors importers make with CNC machined parts from China follow from the points above: no general-tolerance class on the drawing, supplier-typed material certificates, no melt-and-pour record, Section 232 declared on metal content after 6 April 2026, and complete CAD sent to many RFQ recipients before any agreement is signed. One more is easy to miss: omitting finishing specifications, such as anodize type and class or plating thickness, along with the time a subcontracted finisher adds.

Evaluating a shop uses the same checklist in reverse. Ask which processes are done in-house and which are subcontracted, since finishing and heat treatment are often outside the shop's control. Ask for a sample CMM report and an FAI in the format the program needs. Ask how material is bought and whether original mill certificates travel with each lot. Confirm in the purchase agreement who owns the programs and fixtures. A shop that cannot produce these documents for a sample order is unlikely to produce them in production.

Frequently asked questions

Sources

• United Nations Statistics Division (UN Comtrade) — UN Comtrade database, reporter USA, flow imports, HS 848790, 2018 and 2025 (2025, HTML-official)
• United Nations Statistics Division (UN Comtrade) — UN Comtrade database, reporter USA, flow imports, HS 732690, 2018, 2024 and 2025 (2025, HTML-official)
• United Nations Statistics Division (UN Comtrade) — UN Comtrade database, reporter USA, flow imports, HS 761699, 2018 and 2025 (2025, HTML-official)
• Executive Office of the President / Federal Register — Proclamation 11021, Strengthening Actions Taken To Adjust Imports of Aluminum, Steel, and Cop… (2026, PDF)
• Office of the United States Trade Representative — USTR, Notice of Actions in Section 301 Investigations ... Failure ... to Impose and Effectively E… (2026, PDF)
• Office of the United States Trade Representative — 2026 Special 301 Report (citing OECD-EUIPO studies) (2026, PDF)
• whitehouse.gov/wp-content/uploads/2026/04/ANNEXES-I-A-I-B-II-III-IV.pdf
• content.govdelivery.com/bulletins/gd/USDHSCBP-4117593