Guide · Machine shops and fabricators

How to track material certs and heat numbers in a small machine shop

A practical way for a small machine shop to tie every mill cert and heat number to the parts it went into, so an audit or a customer question takes minutes, not a day.

If you make parts for aerospace, medical, defence or anyone with a quality system, sooner or later a customer asks: which batch of material went into these parts, and where is its certificate? If the answer lives in a binder, a shared drive and somebody's memory, that question costs hours. Here is a simple system that works in a small shop, with or without software.

What you are actually tracking

• The material cert (often called a mill test report or MTR): the supplier's document stating the material's grade, chemistry and properties.
• The heat number (or lot number): the identifier stamped or tagged on the material that matches the cert.
• The link from that heat number to every job, and every part, that used it.

The first two arrive with the material. The third is the one shops lose, because it has to be recorded at the moment material is cut, by the person cutting it.

1. Check certs at the door, not at the audit

When material arrives, compare the heat number on the bar or plate with the heat number on the cert before anything goes on the rack. Check the grade and specification against your purchase order. If anything doesn't match, set the material aside and call the supplier the same day. A mismatch found at receiving is a phone call; found after machining it is scrap.

2. Give every heat its own home and label

Keep material from different heats physically separate, and label the rack position with the heat number. If you cut a bar into pieces, mark the heat number on each remnant before it goes back. A remnant with no marking is material you can no longer use on certified work.

3. Record the heat number on the job, when it is cut

Make the heat number a required field on your traveller or job record, filled in by whoever pulls the material. Not at the end of the week, and not from memory: at the saw. This single habit is what makes a later trace possible.

4. Keep the cert where the job can find it

File certs by heat number, digitally if you can (a scan or the supplier's PDF), and reference the heat number on the job. Then, from either direction, you can go from a part to its cert, or from a cert to every part made from it, which is what you need if a supplier ever recalls a heat.

5. Practise the trace

Once a quarter, pick a shipped job at random and time how long it takes to produce its material certs. If it takes more than a few minutes, find where the chain broke (usually step 3) and fix that habit. Auditors are less interested in perfection than in seeing that you test your own system.

The checklist

• Heat number on the material matches the cert, checked at receiving.
• Grade and specification match the purchase order.
• Each heat stored separately and labelled; remnants marked.
• Heat number recorded on the job when material is cut.
• Cert filed by heat number and findable from the job.
• A trace practised every quarter.