Material Test Report MTR Guide for CNC Machined Parts
For many CNC machined parts, dimensional accuracy is only one part of quality control. The buyer also needs confidence that the material itself is correct. A part machined perfectly from the wrong alloy, wrong temper, or wrong heat lot can still fail in service. That is why Material Test Reports, often called MTRs or mill test reports, matter in CNC machining supply chains.
An MTR is a document that connects a supplied material batch to chemical composition, mechanical properties, heat number, specification and traceability data. It is especially important for regulated, regulated, energy, automation, tooling, food equipment, marine and safety-related components.
Key Takeaways
- An MTR confirms material identity, chemistry, mechanical properties and traceability for a material batch.
- CNC buyers should request MTRs before production when material grade, strength, corrosion resistance or compliance is important.
- MTRs do not replace dimensional inspection. They complement CMM reports, FAIR documentation and certificates of conformance.
- The RFQ should clearly state whether an MTR is required, whether original mill certificates are needed, and whether traceability must be preserved through production.
What Is a Material Test Report?
A Material Test Report is a quality document issued by a mill, distributor or material supplier. It summarizes test results for a specific material batch. For metal CNC machining, the report may include chemical composition, tensile strength, yield strength, elongation, hardness, heat treatment condition and applicable material standards.
Common names include:
| Term | Meaning |
|---|---|
| MTR | Material Test Report |
| Mill Test Report | Report from the mill or material producer |
| Material Certificate | General term for material proof document |
| EN 10204 3.1 Certificate | European inspection certificate type often requested for metals |
| COC | Certificate of Conformance, often broader and less detailed than an MTR |
The exact format varies by material, supplier and standard.
When Do CNC Buyers Need an MTR?
Not every machined part requires an MTR. For a simple prototype bracket used only for fit testing, a material certificate may not be necessary. But if the part has functional, compliance, safety or customer approval requirements, the MTR should be requested during RFQ.
Request an MTR when:
- The drawing or purchase order specifies a controlled material grade
- The part operates under load, pressure, heat, wear or corrosion
- The customer requires traceability
- The project is for regulated, regulated, energy, defense, food equipment or regulated machinery
- The material is expensive or frequently substituted
- Heat treatment or hardness is critical
- FAIR or PPAP-style quality documentation is required
If an MTR is required after production starts, it may be too late to preserve proper traceability. State it early.
What Information Should an MTR Include?
A useful MTR should identify the material and show evidence that it meets the required specification. Buyers should check whether the report includes:
- Material grade and standard
- Heat number or batch number
- Chemical composition
- Mechanical properties
- Heat treatment or temper condition
- Product form such as bar, plate, tube or casting
- Supplier or mill name
- Test date or certificate date
- Applicable standard or specification
- Authorized signature or quality approval
For aluminum, temper such as T6, T651 or T7351 can matter. For stainless steel, grade and chemistry are critical. For tool steels and hardened steels, hardness and heat treatment condition may be essential.
MTR vs COC vs CMM vs FAIR
These documents are often confused, but they serve different purposes.
| Document | What It Proves | CNC Use |
|---|---|---|
| MTR | Material chemistry and properties | Confirms material batch compliance |
| COC | Supplier statement of conformance | General compliance confirmation |
| CMM Report | Dimensional measurement results | Confirms part dimensions |
| FAIR | First Article Inspection Report | Confirms first production article meets drawing requirements |
| Hardness Report | Hardness test result | Confirms heat treatment or material condition |
An MTR tells you what the material is. A CMM report tells you what the machined part measures. A FAIR connects the manufactured part to the drawing requirements. For critical components, buyers may need all three.
Common Material Traceability Risks
Material documentation can fail in several ways:
- The RFQ did not mention MTR requirements, so the supplier bought standard stock without traceability.
- The material certificate exists but does not match the actual batch used for the parts.
- The certificate lists the grade but not the temper or heat treatment condition.
- The supplier substituted a similar material without written approval.
- The certificate was lost when material was cut into smaller blanks.
- Parts from different material lots were mixed during production.
For quality-critical CNC projects, traceability must be planned before material purchase and maintained through cutting, machining, finishing and shipment.
How to Request an MTR During CNC RFQ
Use clear RFQ language. For example:
Material: 6061-T6 aluminum. Original mill certificate / MTR required. Maintain batch traceability through production. Include MTR with shipment documentation.
Or:
Material: 316L stainless steel per specified standard. MTR required with chemistry and mechanical properties. No material substitution without written approval.
If only a COC is required, say that instead. If full traceability is mandatory, state it explicitly.
MTR and Surface Finishing
Surface finishing can complicate traceability. If parts are sent to anodizing, plating, passivation, heat treatment or coating partners, the supplier should maintain lot identity through the outside process. For critical work, ask whether finishing certificates or coating thickness reports are also required.
The MTR proves the base material. It does not automatically prove that finishing was performed correctly.
How Andas Precision Handles Quality Document Planning
Andas Precision helps buyers clarify QA documentation before formal quotation. If an RFQ requires MTR, CMM report, FAIR-style documentation, COC, hardness report or coating documentation, those requirements should be included with the drawing package. The Andas QA package page provides public guidance on common quality documents for CNC projects.
For the fastest review, upload STEP/STP or IGES geometry, include a PDF drawing, specify material grade, quantity, tolerance requirements, finishing and required quality documents.
FAQ
Is an MTR required for every CNC machined part?
No. It depends on function, compliance, customer requirements and material risk. Critical parts should request MTRs during RFQ.
Is a material certificate the same as an MTR?
Sometimes the terms are used loosely. A true MTR usually includes batch-specific chemistry and/or mechanical properties, while a generic certificate may only state conformance.
Does an MTR prove the part dimensions are correct?
No. An MTR proves material-related information. Dimensional accuracy should be verified with inspection reports such as CMM reports or FAIR documentation.
Can an MTR be requested after machining is complete?
Sometimes, but it is risky. If traceability was not preserved from the start, the supplier may not be able to prove which material batch was used.
What should I include in the RFQ if I need material traceability?
State the material grade, required standard, MTR requirement, traceability requirement, substitution rules and whether the certificate must ship with the parts.