Production managementReading time 11 min
Traceability Limits the Size of a Recall
When a defect appears, the question is which units share the same material, process and inspection history. Serial-level records can turn a broad recall into a targeted one—if the links were captured along the way.
01Lot or serial number?
| Lot traceability | Unit serial traceability | |
|---|---|---|
| Granularity | One lot (hundreds to thousands of units) | Every unit |
| Cost | Low | High, marking, reading, data volume |
| Recall scope | The whole lot | Down to the individual unit |
| Typical use | Fasteners, raw material, consumables | Automotive safety parts, medical devices, aerospace |
| Data volume | Small | Large; needs a database design |
02Choosing a code
| Type | Dimensions | Capacity | Characteristics |
|---|---|---|---|
| Code 128 | 1D | about 48 characters | General purpose, dense |
| Code 39 | 1D | Lower | Legacy systems, self-checking |
| EAN / UPC | 1D | Fixed | Retail goods |
| QR Code | 2D | Thousands of characters | High error tolerance, phone readable |
| DataMatrix | 2D | Thousands of characters | Readable at very small sizes; the default for industrial marking |
| PDF417 | Stacked | Medium | ID cards, logistics labels |
03Checking direct marks
A code marked directly on metal is judged differently from a printed label. Direct-part marking has its own verification standard, ISO/IEC 29158, because surface texture, lighting and marking method affect readability. Decide how the code will be verified before choosing the mark.
| Metric | What it looks at |
|---|---|
| Cell Contrast | Whether cell-to-background contrast is sufficient |
| Cell Modulation | How consistent the cell brightness is |
| Fixed Pattern Damage | Whether the finder pattern (L and clock track) is intact |
| Axial Non-uniformity | Whether the code's aspect ratio is distorted |
| Grid Non-uniformity | Whether the grid positions have drifted |
| Unused Error Correction | How much error correction margin is left |
Marking method affects how a code is read and verified. Laser annealing, engraving and dot peening leave different contrast and surface changes. Choose a location and method that preserve the part's function as well as the code's readability.
04Numbering rules
- Do not encode meaning into the serial. Packing part number, date and plant code into the serial looks convenient until the scheme changes and the old numbers stop parsing, and the length gets away from you.
- Let the serial be nothing but a key. Everything else lives in the database, so adding a field does not invalidate parts already marked.
- Design against mistakes. A check digit (Mod 43, say) blocks manual entry errors.
- Follow the sector standard. Automotive commonly uses VDA 4902 or AIAG B-4 label formats; medical devices use UDI; aerospace uses ATA Spec 2000.
05Connecting the records
A usable trace chain connects material lot, work order, process steps, inspection results, finished serial and shipment. Test that chain by selecting a shipped unit and tracing backward; a missing link will matter most during a recall.
| Link | Data source | Where it commonly breaks |
|---|---|---|
| Raw material | Incoming inspection, mill certificate | The certificate exists only on paper |
| Work order | ERP | — |
| Operations | Shop floor reporting | Verbal handoffs, entered after the fact |
| Inspection | Inspection sheet | Only a checkmark, no measured value |
| Shipment | Delivery note | Not linked to the serial |