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Checking for Forward and Backward Traceability in a Factory

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When investigating quality problems, we are often faced with the same issue: lack of traceability.

Let’s say some metal pieces don’t fit well and this is found at the assembly stage. It typically unfolds as follows:

  • We look at the faulty parts. They are off-tolerance in some critical-to-quality dimensions.
  • We go to the preceding process, for example CNC milling. Unfortunately, the faulty parts were processed 6 days ago and since then they have done a new setup and are working on another part.
  • We ask which of the CNC machines worked on these parts. Nobody knows, since 3 machines worked on that part at the same time.
  • We ask when, and on what machine and what mold, the faulty parts were forged. Again, nobody knows.
  • We ask what material lot (purchased from an outside supplier) they were part of. Again, nobody knows. They might even have spent months in the warehouse, since FIFO (first-in-first-out) is not respected and the logs can’t be trusted.

What is traceability, in a manufacturing setting?

In a good factory, materials can be traced from input to output, throughtout the production and also after the finished product has been shipped out.

It can be represented this way:

Supplied materials (from supplier) >> Semi-finished product >> Semi-finished product……>> Finished product >> Product distribution (distributors etc.)

Traceability is required by ISO 9001, it is mandatory for certain products in certain countries (e.g. food products in Hong Kong), and it is extremely useful for finding the cause of quality/safety issues.

What are the main benefits of traceability?

  • Easier root cause analyses (since the path taken by faulty materials can be followed), faster and more effective resolution of issues.
  • Recalls in the marketplace (very worst case in many industries, from automotive to food) can be minimized, since not all products need to be recalled. If the cause is a bad batch received from a supplier, only the products made with that batch need to be recalled.
  • Increased consumer confidence : traceability gives customers the confidence that what they are buying is legal, safe and fairly traded. This is increasingly important, especially for commodities such as wood, chocolate, etc.

How to check traceability during an audit?

In a company with a good traceability system, an auditor can check forward and backward traceability in a predictable time frame.

I found a good explanation of the difference between forward and backward traceability here:

  • Checking forward traceability: taking a batch of materials/components and tracing them through the process, including work in process, all the way to the finished products that were made with those materials/components.
  • Checking backward traceability – this is taking a finished product batch and tracing it, starting from the customer, back through the process including work in process, all the way to the batches of materials/components received from suppliers.

Let’s take an example to illustrate how to check backward traceability on a production of plastic bottles:

  1. Go to the finished goods warehouse and pick 3-5 samples randomly.
  2. Check if there is a triangle mark (recycling mark) on the bottle — that mark tells consumers which material was used to make the bottle. (1)
  3. Then ask the factory to trace back who is the supplier for the material used for these bottles. Check if their records can prove the link to a supplier.
  4. Check if that supplier is part of the approved supplier list. Check if the factory monitors this supplier regularly.
  5. Ask for the MSDS (Material Safety Data Sheet) or other related test reports.
  6. Check if the documents match the samples you picked at the beginning.

In the production of general hard goods, it is common to place a barcode, a QR code, or an RFID chip, on the parts or on the bin that travels with the parts. There are many ways to achieve that objective.

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Note (1): the recycling mark bears a number between 1 and 7. Numbers 1, 2, 4, and 5, are acceptable for carrying food for a certain period of time. Number 2 is high-density polyethylene (HDPE), it is the most stable material and is most suitable for long term storage.