Key takeaways
- Traceability has to work in both directions: from a shipment back to the heat, and from a heat forward to every shipment.
- A lot is a group of parts made under the same conditions, sized so that containment is possible.
- Marking has to survive plating, washing and heat treatment, or the chain breaks at the process step.
- Test the chain with a real trace exercise and record where it broke, not just whether it passed.
The questions traceability has to answer
Traceability answers four questions: what material went into this part, which process and machine made it, which inspection released it, and where it went. A fifth question follows: who else received the same material or the same lot.
If a customer reports a failure, the chain should let you find the affected shipments and the process condition that produced them. If a mill reports a bad heat, the chain should let you find the parts made from it. Both directions matter, and a system that only works forward is half a system.
Define the lot before you label it
A lot is a group of parts made under the same conditions: the same material heat, the same tool, the same machine, the same process settings and the same shift or a defined period. The lot should be small enough to contain a problem and large enough to be practical.
A lot that covers a week of production on three machines cannot support a recall. A lot that covers ten pieces creates more labels than the line can manage. Set the rule by process and by the cost of containment, then write it into the work instruction.
The chain from heat number to shipment
The chain is only as strong as the weakest link. Each link needs an identifier that appears in a record, and the records need to be linkable to each other without a person remembering the connection.
A certificate with a heat number that never appears on the receiving record is not a link. A work order that does not name the lot is not a link. The table shows the links that have to close.
| Link | Identifier | Where it is recorded | What it proves |
|---|---|---|---|
| Material | Heat or coil number | Mill certificate and receiving record | Which material went into the lot |
| Process | Work order, date and shift | Route card and machine log | Which process ran, when and on what equipment |
| Inspection | Lot code and sample record | Inspection file and control plan | Which results released the lot |
| Shipment | Packing list and invoice | Dispatch record and customer receipt | Where the lot went and in what quantity |
| Rework | Rework order and lot suffix | Rework record and reinspection | Whether the lot changed condition after the first release |
A link that exists in one system but not the next is a break. Follow a real lot through all five before you call the system complete.
Marking that survives the process
Marking has to survive the process. Ink on a part can disappear in a plating bath, a wash or a heat treatment. A tag can fall off a bundle. A label can be covered by packaging.
Choose the method for the route: laser marking, stamping, an etched code, a tag fitted after finishing, or a label on the bag. Verify the code after every process that could remove it, and define what to do if it becomes unreadable.
Never re-mark a part without a record. A new label on an old part is a new identity unless the link to the original lot is written down. The person who re-marks a part is creating evidence, and the record should say so.
Records and retention
Follow the contract, the customer requirement and the regulation for retention. Keep the receiving record, the mill certificate, the route card, the inspection record and the shipment record for the same period, so the chain does not end halfway through.
Paper records work if they are indexed by lot. Electronic records work if the lot field is mandatory and the system does not allow a blank. A scanned certificate with no lot reference is a picture, not a record.
Test the chain with a trace exercise
Run the exercise twice a year, or after a system change. Pick a shipment and walk backward to the heat. Pick a heat and walk forward to every shipment. Time the exercise and record where the chain broke.
A trace exercise that takes a day for one lot is a finding. It is better to learn that in a practice run than during a customer complaint, when the clock is running and the customer is holding stock.
Rework, mixed lots and regrading
Rework creates a new condition. Give the reworked lot a suffix or a new lot number, record the operation, the inspection and the person who released it. Do not return reworked parts to the original lot without a record.
If two lots are combined, the new container needs both references or a new lot identity that points to both. A label that shows only the newer lot hides the older material and defeats the exercise.
A part that fails a characteristic and is accepted for a lower grade needs a new identity and a record of the concession. Regrading without a new identity turns a controlled decision into an untraceable one.
Flow the requirement to the supplier
The purchase order should require the material certificate with the heat number, the lot code on the label and the packing list, and the inspection record linked to the lot. Put the requirement in the quality agreement, not only in an email.
Audit the requirement at goods-in. If the lot code is missing, reject the paperwork before the material enters the line. A traceability system that starts after receiving cannot answer the first question.
The chain is proven, not declared
A procedure that says every lot is traceable is a claim. A trace exercise that walks a real shipment back to a real heat is evidence.
Frequently asked questions
How big should a lot be?
Small enough that a containment can be targeted, and large enough that the labelling and records are practical. The limit should follow the process: a heat, a shift, a tool run or a defined quantity. Write the rule down and apply it consistently.
Does traceability require marking every part?
Not always. The requirement is that the lot can be identified and linked to the shipment. For small parts, the label on the bag or the box may be the practical identifier. Where a part can be separated from its packaging, agree a method that survives the process.
What is a trace exercise?
It is a practice run in both directions: pick a shipment and follow it back to the material, then pick a material lot and follow it forward to every shipment. Record the time, the breaks and the corrective action.
How long should traceability records be kept?
Follow the contract, the customer requirement and the regulation for the part. The record should cover the production life and the period in which a field question or recall could arise. Keep all the links for the same period.
Sources and further reading
- ISO 9001:2015, clause 8.5.2, Identification and traceability
- IATF 16949:2016, clause 8.5.2.1, Identification and traceability, supplemental
- EN 10204, Metallic products, Types of inspection documents
Qumek Quality Desk
Quality team
The quality team responsible for first article inspection, PPAP packs, supplier audits and the records shipped with production parts.
Testing a traceability chain?
Send a recent shipment record and the material certificate. The quality desk will walk the chain in both directions and mark the breaks.
Send the records