Problem & Solution
Material Verification Red Flags on Delivered CNC Parts
Material substitution and documentation fraud are rare but real risks in machined-parts supply. A part that's labeled Inconel 718 but delivered as 316 stainless will fail catastrophically in service. This guide covers what to verify on delivery and the red flags that indicate a supplier problem.
What can go wrong
Common material problems: outright substitution (wrong alloy delivered), wrong heat-treat condition (H900 delivered as H1150 or vice versa), off-spec chemistry within an alloy family, undocumented material with fabricated MTRs, and material from unqualified sources with unknown provenance.
The consequences: part fails in service; supplier claims 'it's the right material' with a fake MTR; buyer has to prove what happened. Prevention is verification at receiving, not investigation after failure.
What to verify at receiving
- Certificate of Conformance and MTR reconciliation. MTR should match the part's specified alloy grade, chemistry range, and mechanical properties. Heat and lot numbers must match the supplier's CofC and internal shop-order paperwork.
- PMI (positive material identification) on critical parts. Portable X-ray fluorescence or optical emission spectroscopy verifies the actual alloy. For high-consequence-of-failure parts, worth the $50–$200 test per lot.
- Hardness check. Confirms heat-treat condition. 17-4 PH H900 should be 40–45 HRC; if hardness is 30 HRC, it's been delivered in Condition A or overaged.
- Dimensional verification against first-article report. Confirms the part matches the FAI drawing, not just any print with the correct part number.
- Physical inspection for defects. Cracks, laminations, scale, unexpected surface texture — all can indicate material problems.
Red flags in supplier documentation
- MTR chemistry looks 'too clean' — Real mill test reports show minor variations; suspiciously round numbers are a fraud indicator.
- CofC missing key details — Missing heat/lot numbers, missing signature, missing date. Real documentation is complete.
- Same MTR appears on multiple deliveries — Real mill test reports are heat-specific. Same MTR for different batches indicates fraud or laziness.
- Supplier resists PMI verification — Serious suppliers welcome PMI as confirmation. Resistance is a signal.
- Documentation delayed after delivery — "We'll send the paperwork next week" is a red flag. Documentation should ship with the parts.
Frequently asked questions
Is PMI verification worth the cost on incoming parts?
For high-consequence-of-failure parts, absolutely. $50–$200 per lot is trivial vs the cost of a service failure. For low-consequence commodity parts, MTR review + hardness check is usually sufficient.
What if my supplier's MTR looks suspicious?
Contact the mill directly and verify the heat/lot number. Real mills confirm their MTRs. If the mill doesn't recognize the heat, the MTR is fabricated.
How do I qualify a new supplier's material sourcing?
Audit their material-receiving process. Ask to see recent MTRs, their PMI protocol on incoming material, and their heat/lot documentation flow. A supplier who can't show these has documentation gaps.
Does B&R Productions do PMI on incoming stock?
For customer-specified critical work, yes. Standard practice is heat/lot documentation against MTR; PMI adds an additional verification layer available on request.