When you order CNC machined parts, you're not just buying shapes — you're buying verified material properties. The difference between a certified 316L stainless steel medical component and an unverified "stainless steel" part could be the difference between a successful device and a catastrophic failure.
Material certifications provide documented proof that the raw material used in your parts meets specified chemical, mechanical, and regulatory requirements. This guide covers the essential certifications every buyer should understand: Mill Test Reports (MTRs), RoHS, REACH, conflict minerals compliance, and industry-specific requirements.
A Mill Test Report (MTR), also known as a Certified Mill Test Report (CMTR) or Material Test Certificate, is a document issued by the material manufacturer (the mill or foundry) that certifies the actual chemical composition and mechanical properties of a specific production lot (heat) of metal.
An MTR typically includes:
The European standard EN 10204 defines different levels of material inspection documents. Understanding these levels helps you specify the right certification:
| Type | Name | Who Issues | Description |
|---|---|---|---|
| 2.1 | Declaration of compliance | Manufacturer | Statement that material meets order requirements, no test results |
| 2.2 | Test report | Manufacturer | Includes test results from non-specific inspection |
| 3.1 | Inspection certificate | Manufacturer's QA (independent of production) | Test results from specific inspection of delivered lot |
| 3.2 | Inspection certificate | Manufacturer's QA + authorized inspector | Highest level — verified by independent third party |
For most precision CNC applications, EN 10204 3.1 certification is the standard requirement. It provides lot-specific test results verified by the mill's quality department. The 3.2 certificate, requiring a third-party inspector present at testing, is typically reserved for nuclear, critical pressure vessel, and military applications.
The Restriction of Hazardous Substances (RoHS) directive is an EU regulation that restricts the use of specific hazardous materials in electrical and electronic equipment (EEE). The current version (RoHS 3, EU Directive 2015/863) restricts 10 substances:
| Substance | Maximum Concentration | Relevance to CNC Parts |
|---|---|---|
| Lead (Pb) | 0.1% (1000 ppm) | Free-machining alloys (12L14, leaded brass), solder |
| Mercury (Hg) | 0.1% | Rarely relevant to machined parts |
| Cadmium (Cd) | 0.01% (100 ppm) | Some plating processes, older brazing alloys |
| Hexavalent chromium (Cr6+) | 0.1% | Chromate conversion coatings, some passivation |
| PBB | 0.1% | Not relevant to metal parts |
| PBDE | 0.1% | Not relevant to metal parts |
| DEHP, BBP, DBP, DIBP (4 phthalates) | 0.1% each | Some plastic components, packaging |
RoHS significantly affects material choices for CNC machined parts:
REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) is an EU regulation that addresses the production and use of chemical substances. Unlike RoHS, which targets specific substances in EEE, REACH is much broader — covering all chemicals manufactured or imported into the EU above 1 tonne per year.
For CNC parts, REACH primarily applies through:
The Dodd-Frank Act Section 1502 (US) and EU Conflict Minerals Regulation require companies to investigate whether their products contain tin, tantalum, tungsten, or gold (3TG) originating from conflict-affected regions, primarily the Democratic Republic of Congo (DRC) and adjoining countries.
For CNC parts, this primarily affects:
Suppliers are expected to complete Conflict Minerals Reporting Templates (CMRT) developed by the Responsible Minerals Initiative (RMI). Most reputable CNC manufacturers maintain updated CMRT forms for their customers.
Getting the right certifications starts with clear communication at the quoting stage. Here's a practical approach:
Include certification requirements directly on your drawing or purchase order. For example:
Most certifications don't add significant cost when specified upfront. However, requesting certifications after material has been ordered may be impossible (if the mill didn't retain samples for testing). The cost of certification is typically:
Receiving a certificate is step one. Verifying it is equally important:
A Mill Test Report (MTR), also called a Material Test Report or certified mill test report (CMTR), is a document from the material manufacturer that certifies the chemical composition and mechanical properties of a specific heat or lot of metal. It proves the material meets the specified alloy standard (e.g., ASTM A276 for stainless steel bar).
If your CNC parts are used in electrical or electronic equipment sold in the EU, they must comply with the RoHS directive, which restricts lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE. Even non-EU markets increasingly require RoHS compliance as a procurement standard.
RoHS restricts specific hazardous substances in electrical/electronic equipment (6 substances + 4 phthalates). REACH is broader — it regulates all chemicals manufactured or imported into the EU above 1 ton/year and maintains a growing Substances of Very High Concern (SVHC) candidate list. A part can be RoHS compliant but still have REACH obligations.
For critical applications (medical, aerospace, automotive safety), always request MTRs and relevant compliance certificates. For general commercial parts, requesting certifications on the first order and periodically thereafter is good practice. The cost of obtaining certifications is minimal compared to the risk of using non-conforming material.
EN 10204 3.1 is a European standard for material inspection documents. A 3.1 certificate is issued by the material manufacturer's quality department (independent of production) and certifies that the material meets the specified requirements based on specific inspection and testing of the delivered lot. It is the most commonly requested certification level for precision CNC parts.
KING HAN provides EN 10204 3.1 material certificates, RoHS/REACH compliance declarations, and full lot traceability as standard practice. We source from certified mills and maintain complete documentation for every order.
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