Automotive customers do not ask for traceability as a feature. They ask for evidence that a specific vehicle or component received a specific operation, at a specific station, with a specific result. The line has to produce that evidence automatically.
Key takeaways
- Define the traceability unit first: vehicle, assembly, component or batch.
- Every critical operation needs a read, a result and an interlock.
- The PLC must stop the line or reject the part when data is missing.
- Store data locally and forward it to MES; do not rely on one system.
Step 1: define the traceability unit
For a seat line, the unit may be the seat assembly with a unique label. For an engine line, it may be the engine serial number. For a stamping line, it may be the coil or the batch. The unit determines where labels are applied, where they are read and how long the data is kept.
Choose a carrier that can hold the label through the process. A paper label may not survive washing or painting; a laser-marked code or an RFID tag may be needed. The carrier and the label should be designed together.
Step 2: place read stations at decision points
A read station is needed wherever the line makes a decision based on the product: before a variant-specific operation, before a test, and at the end of the line. A read at the start and a read at the end is not enough; the line cannot prove the middle operations.
Place the reader so that the code is presented consistently. A handheld scanner relies on the operator; a fixed scanner with a defined field of view is more reliable. For high-speed lines, use a scanner with a trigger from a photo-eye and a reject gate if the read fails.
| Operation | Data to capture | Interlock |
|---|---|---|
| Component pick | Part number, batch | Wrong part rejects |
| Torque | Torque, angle, tool ID | Out-of-limit rejects |
| Test | Result, test program, time | Fail rejects |
| Label apply | Label content, read-back | Mismatch rejects |
| Final inspection | Inspector, result | Fail blocks shipment |
Step 3: interlock the PLC
The PLC must prevent the next operation if the previous result is missing or out of limit. This is the difference between traceability and a database. A line that records data but allows a part to continue after a failed torque is not traceable in the sense the customer means.
Design the interlock so that a rejected part is routed to a rework area, not left on the line. The rework area needs its own read station and its own record, so the part's history is complete.
Step 4: store and forward
Store data locally for at least the retention period required by the customer, and forward it to MES or a central historian. Local storage protects against network outages; central storage makes the data available for analysis. Use a time stamp from a single source and synchronise it across stations.
Define what happens when the network is down: the line should continue to record locally and forward when the connection returns. A line that stops because MES is unavailable loses output for a reason unrelated to production.
Step 5: handle errors and exceptions
Define the response to a failed read, a missing label, a duplicate serial number and a part that is reworked. Each case needs a procedure and a record. Operators should be able to resolve a failed read without calling engineering, but the resolution must be logged.
For duplicate serial numbers, the line should reject the part and alert the supervisor. A duplicate can indicate a labelling error or a part that has re-entered the line from rework.
Audit and retention
Keep records for the period specified by the customer and the applicable regulation. For automotive, this is often 15 years or the vehicle lifetime. Design the storage and backup to meet that requirement, and test a restore before the first audit.
Make the records easy to query by serial number, by date and by station. An auditor should be able to trace a vehicle from final assembly back to the component batches in minutes, not days.
Frequently asked questions
Do I need RFID or is a barcode enough?
A barcode is enough for most assembly lines if the code can be read reliably at each station. RFID is useful where the tag is not visible or where the part must be identified at a distance.
How long should traceability data be kept?
Follow the customer and regulatory requirement, which is often 15 years for automotive. Confirm before designing the storage.
What if the network goes down?
The line should record locally and forward when the connection returns. Do not stop production because MES is unavailable.
Send your traceability requirement and station list to our engineers through the contact page; we will design the read points and interlocks with the line.
