Tracciabilità dei lotti con il kanban: è possibile? Guida pratica

Why lots are a problem in kanban systems

Kanban is essentially a material replenishment system, not an identification system. The card is linked to a part number and a fixed quantity, and it goes back into circulation unchanged at every cycle: the same card that travels with lot A today will travel with lot B two weeks from now.

Lot traceability, on the other hand, is the ability to reconstruct, for each lot, which supplier it came from, when, which finished products it was used in and which customers it was shipped to. The two approaches do not contradict each other, but they do not overlap either: basic kanban keeps no record of which lot it accompanied.

How to trace lots with kanban: 4 practical methods

There are 4 practical methods for tracing lots with kanban cards, and they can be combined. Keep in mind, however, that the more rigorous they are, the more traceability improves, but the more manual work they require.

Method 2: strict FIFO in the supermarket

Gravity racks, flow lanes or picking rules that ensure the material stored longest is used first guarantee that lots are consumed in order of arrival. This way, knowing the arrival dates, you can estimate fairly accurately when a lot entered production.

Pros: nothing needs to be written down, because the order is determined by the physical layout. It also reduces the risk of having expired or deteriorated material in stock.
Limitation: it is an estimate, not a record. A single out-of-sequence pick invalidates the entire estimate.

Method 4: card with a marker-pen lot field (or document pocket)

Some companies add an erasable field to the card, or a pocket to hold the delivery note of the lot in use.

Pros: it costs almost nothing, and operators can see immediately, at the line, which lot they are using. It is also useful for in-process quality checks.
Limitation: the information is erased at the next cycle, so no history is kept. Useful for identification, not for traceability.

Making traceability possible with electronic kanban

As you may already have heard, kanban does not only exist in its “traditional” form, with paper cards reused across replenishment cycles. For several years now there has also been electronic kanban (or e-kanban), the digital version of the kanban method in which the information on the cards is managed through software.

It is precisely this history that makes traceability possible, in three ways:

• Automatic history: each card has a unique identifier, and the software records when it was released, accepted by the supplier, shipped, received and consumed. Nothing needs to be transcribed or re-entered.
• Automatic reconstruction of links. In the KanbanBOX electronic kanban software, for example, the Track and Trace module links component cards to finished product cards by comparing the time windows of component consumption with the processing periods of a finished product.
  This makes it possible to trace both the finished products that may contain a defective component and the components that may have been used in a disputed finished product.
• Supplier identification. If suppliers are connected to the electronic kanban system (through purchasing kanban), information such as shipment number and delivery date is also recorded by the software. This way, traceability starts not only from material consumption, but from its arrival at the plant.

The physical traceability methods described in the previous section remain useful: one lot per container and FIFO make the electronic data even more accurate. The difference is that recording no longer depends on filling in a form, but happens with a simple scan.

Example: what happens when a supplier reports a defective lot

Imagine a mechanical engineering company that manufactures valve assemblies, Valvole Srl. Its gasket supplier (Guarnizioni Spa) reports that lot L-2417 has a compound defect. Valvole Srl wants to know where the components from that lot were used.

With a traditional kanban system

• Valvole Srl’s quality manager looks for the delivery note for lot L-2417 to find out when it arrived.
• They retrieve the container opening logs for that period, if they were filled in.
• They cross-check the dates with production orders and then with customer shipments.
• If a log is missing, as a precaution they quarantine all material produced in those weeks.

Time required: hours, with no guarantee of finding the information needed.

h2 style=”color: #cb333b;”>Checklist: does your traceability system hold up?

Answer these questions about your current system. Every “no” is a point where the chain can break.

• Does each container hold only one lot?
• Is the lot number visible on the container until it is fully consumed?
• Does picking always follow FIFO (First-In, First-Out), even on night shifts and during peaks?
• Are the opening and consumption of each container recorded with date and time?
• Can the history be consulted in one place, without having to re-enter data?
• Can you link a component lot to finished products in less than an hour?
• Can you also go the other way, from finished product to components?

If you answered “no” to three or more questions, it is worth considering a system that records this data automatically. Book a KanbanBOX demo to see how Track and Trace works on your own part numbers.