Which Quality Documents Are Worth Asking For

By CNC Machining Vietnam·Published September 21, 2026·Editorial standards

Asking for “full quality documentation” produces a folder nobody reads and a line on the invoice. Asking for three specific documents produces evidence. This is what each one is, who issues it and what it actually proves.

The documents, and what each proves

Document	Issued by	Proves	Worth asking for
Certificate of conformity	The machine shop	That the supplier declares the goods meet the order	Always, it is effectively free
Material certificate	The mill, passed on by the shop	Chemistry and mechanical properties of the raw stock	Whenever material properties are functional
First article inspection report	The shop or a third party	That the setup produced a correct first part	First order and after every revision
Dimensional report	The shop	Measured values on production parts	On critical features, at an agreed sample rate
Plating or coating certificate	The finishing subcontractor	Thickness, process and specification compliance	Whenever a coating is functional
Heat treatment certificate	The heat treater	Process, temperature profile and achieved hardness	Whenever heat treatment is specified
Calibration certificates	Accredited calibration lab	That the measuring equipment is trustworthy	On request during vetting, not per order
Packing list	The shop	What is in each box	Always

The four that carry real weight for a typical commercial machined part are the material certificate, the first article report, the dimensional report and, where relevant, the coating certificate. The rest are context or administration.

Material certificates and the traceability question

A material certificate states the chemistry and mechanical properties of a heat or batch of raw material. It is issued by the mill and passed down the chain.

The question that matters is not whether a certificate exists, it is whether it corresponds to the stock your parts were cut from. In a shop buying from a local stockist, the chain is mill to stockist to shop, and traceability depends on the stockist keeping heat numbers attached to material as it is cut.

So ask for it at the order stage, not at the shipment stage. A shop that knows a certificate is required buys stock that carries one. A shop asked afterwards is trying to reconstruct a chain that may already be broken.

If the grade is genuinely functional, for a pressure part, a structural part or anything where a substitution would be unsafe, say so explicitly and ask that the heat number is recorded against your order.

Dimensional reports: the sampling question

A full dimensional report on every piece is rarely necessary and is always expensive. A report on nothing is worse. The middle is where the value is.

Agree three things before production:

1. Which characteristics are reported. The critical features you marked on the drawing, not all of them.
2. What sample. Every piece for the critical features, or an agreed sample per batch. Say which.
3. What format. Actual measured values in a table, referenced to a ballooned drawing.

A report with numbers on five critical characteristics across an agreed sample is more useful than a hundred page document of ticks, and it costs less. The tolerances guide covers how to decide which characteristics belong on that list.

Coating and heat treatment certificates

These are the documents most often missing, because the process was subcontracted and the paperwork stopped at the subcontractor.

For anodising, plating or painting, ask for the specification, the class or thickness achieved and the process used. For heat treatment, ask for the achieved hardness and where it was measured.

Both matter because these are the processes you cannot verify by looking. A part that was anodised to the wrong thickness looks identical to one that was not, right up until it corrodes in service.

Certificates that describe the supplier, not the part

ISO 9001 and its sector variants describe a management system. They tell you that procedures are documented and audited. They do not tell you that your part is correct.

Treat them as one input during vetting, alongside the machine list, the inspection equipment and the sample report. A certificate plus evidence about your part is a strong position. A certificate alone is a filing cabinet.

Also note that certification schemes differ. A certificate issued by an accredited body carries more weight than one from an unaccredited registrar, and the accreditation is checkable.

What to write into the purchase order

Be specific and short:

Documents required with this order: certificate of conformity, material certificate traceable to the stock used, first article inspection report with actual measured values on a ballooned drawing before production, dimensional report on characteristics 3, 7 and 11 for every piece, and a coating certificate stating achieved thickness. All documents to be sent electronically before shipment. Originals to travel with the goods.

The phrase before shipment does the work. Documents that arrive with the goods cannot prevent anything. Documents that arrive before the goods leave can stop a shipment that should not go.

Filing, so it is useful later

Keep the document set per shipment, not per part number. When something goes wrong eighteen months later, the question is always “which batch”, and the answer lives in the packing list, the material certificate heat number and the dimensional report for that shipment.

This is the same discipline as the trade document set described in the importing guide, and for the same reason: the second order is far easier when the first one is documented properly.

The short list

If you ask for three things, ask for these: a material certificate that matches the stock used, a first article report with real numbers before production and a dimensional report on the features you actually care about. Everything else is either free or optional.

Put them on the RFQ rather than in a later email, so the cost sits inside the quote. Send the drawing here and list the documents you need.

Frequently asked questions

Keep reading

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