Production managementReading time 11 min
Serial-level traceability pays for itself on the day something goes wrong
Traceability is worthless on an ordinary day and decisive on a bad one, it decides whether you recall three hundred units or thirty thousand.
01Lot number 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 |
02Barcode types
| 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 |
03Grading a direct part mark
A code cut into metal is not graded the same way as one printed on a label. ISO/IEC 29158 exists specifically to grade DPM quality:
| 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 |
The marking method drives the grade. Laser annealing removes no material and builds contrast through oxide colour, which suits stainless and corrosion-sensitive surfaces. Dot peen is cheap but low contrast. Laser engraving gives the best contrast but breaks the surface, and the mark can become a fatigue initiation site, which is why drawings often restrict where marking is allowed.
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.
05The data has to connect
A complete trace chain runs raw material lot → work order → operation reporting → inspection results → finished serial → customer shipment. Any link maintained by hand on paper or in a spreadsheet means a recall turns into people cross-checking records, and that time usually costs more than the recall itself.
| 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 |