Two Directions, One Test

Traceability has a backward direction and a forward direction. Backward asks: given a finished carton, which raw material lots, machines, operators and parameters produced it? Forward asks: given a raw material lot, which finished cartons contain it, and where did they ship? A factory usually has one direction and believes it has both.

The audit test is simple and slightly cruel: take one carton from the warehouse, without warning, and ask the factory to reconstruct it. Then take one raw material lot from the store and ask where it went. Time both exercises.

Define the Batch Before You Follow It

Ask what a batch means at each process step. The definition is often inconsistent, and that inconsistency is the root of most traceability failures.

  • Weaving: a beam, a loom-day, or a roll?
  • Dyeing: a vessel load, a day, or a customer order?
  • Molding: a shift, a tool run, or a material lot?
  • Plating: a barrel load, a rack, or a day's production?
  • Assembly: a work order, a lot, or a carton range?

A traceability chain is only as precise as its coarsest link. If dyeing traces to a vessel but molding traces to a week, the molded part cannot be linked to a specific tape lot, and the chain is broken at the joint that matters most.

Coding on the Product

Look at a finished zipper and ask what is printed, embossed or labelled on it, and whether that code can be read after plating and assembly.

  • Lot or batch code applied at the point of production, not at packing.
  • Code format that encodes date, process and machine, and can be decoded by staff without a lookup table.
  • Durability of the code through dyeing, plating and washing.
  • Whether the carton label and the inner bag label carry the same lot reference.
  • Whether a mixed carton is permitted, and how it is recorded.

The Record Chain

Walk the chain one link at a time and ask for the record at each link.

  1. Material receipt: supplier lot, quantity, date, inspection result.
  2. Issue to production: quantity, date, work order, and who issued it.
  3. Process record: machine, operator, parameters, quantity in and out.
  4. Transfer between processes: quantity, lot reference, date and receiver.
  5. Final inspection: lot, sample size, result, disposition.
  6. Packing: carton range, quantity, lot and destination.
  7. Shipment: invoice, packing list, container, and date.

At each link, ask what happens when the quantity does not match. A system that cannot handle a mismatch will hide mismatches rather than surface them.

Mass Balance: The Arithmetic That Proves the Chain

Mass balance is the strongest single test of traceability, because it cannot be satisfied by good intentions. For a given period, input weight minus output weight should equal scrap plus process loss within a stated tolerance.

  • Material issued to a process, weighed rather than estimated.
  • Good output plus scrap plus rework, weighed at each step.
  • Process loss allowance, stated as a percentage and justified by process type.
  • Variance identified per lot, with an investigation when it exceeds the tolerance.
  • Scrap sold or recycled, recorded with a destination.

Ask for one month of mass balance for the plating line and one for dyeing. Those two processes are where material disappears most easily, and where an unexplained variance usually means an unrecorded lot.

Mock Recall Under Time Pressure

Run the exercise yourself rather than accepting a description of the procedure.

  • Choose a carton in the finished goods area at random, preferably one from an older order.
  • Ask for the raw material lots, all process records and the shipment details.
  • Record the time to complete, and the number of people involved.
  • Repeat in the other direction, starting from a raw material lot.
  • Ask what the factory would do with the affected stock, and who decides.

A reasonable target is four hours for a complete backward trace with paper records, or under one hour with a functioning system. If the exercise stops because a record is missing, the finding is the missing record, not the speed.

Subcontractors and Bought-In Components

Traceability breaks at the factory gate. Ask how subcontracted lots and purchased components are handled.

  • Whether subcontracted lots receive a new internal lot number on return, linked to the original.
  • Whether the subcontractor provides its own process records, and how long they are retained.
  • Whether purchased sliders or pulls carry a supplier lot that can be traced to a certificate.
  • Whether the factory can identify which shipments contained a specific purchased component lot.

Retention and Retrieval

  • Retention period for each record type, stated in a procedure.
  • Storage that is protected from water, heat and loss, with a backup for electronic records.
  • Whether records from three years ago can actually be found, tested by asking for one.
  • Whether records leave the factory when a customer or auditor requests them, and under what control.

Ask for a record from three years ago. The speed of that retrieval tells you whether retention is a policy or a practice.

The Actionable Audit Checklist

  • Batch is defined at every process step and definitions are consistent.
  • Lot codes are applied at production, not at packing.
  • Codes can be decoded by line staff without a lookup table.
  • Codes survive dyeing, plating and washing.
  • Carton and inner labels carry the same lot reference.
  • Receipt, issue and process records all carry lot references.
  • Quantity mismatches are investigated rather than absorbed.
  • Mass balance is calculated monthly for dyeing and plating.
  • Variance above tolerance triggers a documented investigation.
  • Backward mock recall completed and timed during the audit.
  • Forward trace from raw material lot completed and timed.
  • Subcontracted lots are renumbered and linked to the original.
  • Records from three years ago can be retrieved on request.

What a Passing Answer Looks Like

Passing sounds like this: "Carton four-one-seven decodes to plating barrel twelve on the eighth, molded on line three from resin lot R-two-two-one-nine, and that resin went into three work orders, two of which shipped and one of which is still in the warehouse." That answer is a chain, not a claim, and it can be verified while you wait. Donglong asks for exactly that level of reconstruction before approving a supplier for critical programmes.