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The Kanban system is one of the most effective tools in Lean Manufacturing for reducing inventory and regaining control of material flow in production. The article begins with a comparison between the Push logic (still widespread in many companies) and the Pull logic, where the actual demand drives every material movement, not forecasts.
Kanban is the operational mechanism that puts this logic into practice: a physical or digital card linked to a standard container that, when emptied, automatically triggers a replenishment. There are three main variants (standard, batch, and signal), each suited to different contexts depending on the frequency of consumption and the size of the batches.
A central passage is system sizing: the correct number of cards is calculated based on average demand, lead time, and safety stock, with a numerical example showing how each process improvement directly translates into a reduction in inventory.
Not all materials are suited for Kanban: it works best for components with stable and repeated consumption, while for costly, variable, or unpredictable lead time items, other policies are preferable. The article concludes by framing Kanban within the broader Lean system (JIT, production supermarket, and Takt Time) and with an invitation to train in the field through the Lean Advanced course at Lean Factory School®.
Inventory becomes a problem when it grows more than real demandtake up space, absorb capital, and hide Process inefficiencies. Kanban is precisely for this: to regain control of the flow and restart the material only when it's truly necessary.
In many companies, production still operates with a logic PushPlanning is done in advance based on forecasts, batches are produced, and material is pushed towards downstream departments—regardless of what is actually needed at that moment. The result is almost always the same: high inventories, out-of-control Work In Process (WIP), space occupied by waiting material, and tied-up capital that doesn't create value.
Logic Pull It works in reverse: no department produces or moves material until the downstream process explicitly requests it. Real demand, not forecasts, drives the flow. Each station only works when it receives a request signal from downstream.
Kanban is the operational tool that makes this logic concrete. It is not a theory: it is a physical and visual system that governs the flow of materials and information throughout the entire production chain and, in more advanced cases, all the way to suppliers.
Kanban (看板) means visual signal. In practice, it is a simple and highly effective method for replenishing inventory and managing the flow of information using a pull system.
In practice, Kanban is a Badge — physical or digital — associated with a container holding a standard quantity of a specific component. When the container is empty, the tag is returned to the upstream process as a replenishment order.
There are two fundamental types:
The tag is not a simple post-it note: it is the operational signal that replaces production, picking, and transfer orders.
A well-constructed Kanban card displays:
This visual clarity is the system's strength: anyone, at any time, can understand the workflow status without accessing management software. Control is immediate and decentralized.
There isn't just one Kanban. The right variation depends on the process, the type of material, and how consumption manifests.
For each component, a number of containers is defined with a fixed quantity. Each container is associated with a tag: when the container is empty, the tag serves as a restocking order for the internal or external supplier. This is the most common and easiest form to implement.
It works like standard Kanban, with one difference: the internal or external supplier does not start production upon receiving a single card, but waits for a certain number of cards to accumulate before starting. It is used when the minimum production or purchase lot is significantly larger than the quantity of a single container. It requires special boards for managing waiting cards.
It visually and physically reintroduces the logic of the reorder point. The tag is not associated with a single container; it is sent to the supplier only after a certain number of containers or pieces have been consumed. It is the most suitable solution when consumption is less regular or supply lots are larger.
Kanban system sizing is the most critical step. Too many cards mean excessive inventory; too few mean a risk of stockouts. The number of Kanban cards You get it by dividing the total need to be met, which is the average demand multiplied by the lead time plus the safety stock, by the quantity contained in each container.
The Medium question It is calculated by cross-referencing historical consumption from the last 6-12 months with forecasts for an equivalent period. The Lead Time This is the production time for an internal Kanban, or the procurement time for a Kanban to suppliers. The security escort takes into account fluctuations in demand and the desired service level: the higher the service level, the larger the required safety stock and the lower the risk of stockouts. The choice is always a trade-off between inventory costs and the cost of potential stockouts.
Suppose we manage a fitting flange on Kanban that is used on 8 out of 10 finished products.
The system therefore provides for 8 containers of 25 pieces in circulation. The maximum theoretical supply is 200 pieces — exactly what is needed, no more, no less.
If the upstream process improves and the lead time is reduced from 3 to 2 days, the number of tags required will be 6. Two fewer cards.
Not all components They manage well with Kanban. Its maximum effectiveness is expressed with materials that have regular, predictable, and repeated consumption: those that leave the warehouse every day, in similar quantities, to end up on the same lines.
Imagine a company that assembles electric motors. Out of 300 bill of materials (BOM) references, about 240 are standard components: screws, gaskets, connectors, bearings – codes that are consumed daily with little variability. For these, Kanban works perfectly: standard containers, cards, automatic replenishment. No planner needs to worry about them. The remaining 60 references are expensive components, specific to the model or with long and unpredictable lead times: this is where MRP, or a dedicated supply agreement, is needed.
The rule of thumb is simple: if a component is used in 80% of your finished product codes, has stable demand, and a reasonable lead time, Kanban is almost certainly the right solution. If, on the other hand, the component is expensive, bulky, variable, or critical, it’s worth considering other management strategies.
There is also an even simpler form of classic Kanban, suitable for small, low-value components: the method “empty for full”. Two containers are used: when the first is emptied, it is refilled using the second as a buffer stock. In fact, it's a Kanban with two cards, where the replenishment signal is the empty container itself.
Kanban is not an isolated tool: it is the operational mechanism that brings the Just in Time (JIT). In JIT, each department begins production only if the downstream department has requested a specific item in a defined quantity. The Kanban is precisely the signal that triggers this request, and the mechanism propagates backward along the entire chain, all the way to the suppliers.
Inside the system, the supermarket It is the controlled storage point where Kanban-managed materials are picked by the downstream process and replenished by the upstream process. It is not a traditional warehouse; it is a precisely sized, visible, and self-managed buffer thanks to the cards.
The Takt Time — the pace at which the market absorbs products — is the benchmark that governs the entire system: it defines the speed at which the Kanban must run and therefore the number of cards required to maintain flow without accumulating unnecessary inventory.
Those who introduced Kanban into production often recall a seemingly trivial detail: the first day no one had to look for anything. No phone calls between departments to find out if materials had arrived. No emergency meetings to handle a shortage. The container was in its place, the tag was returned, the flow ran by itself. It's not magic: it's the result of a system designed to make the real state of production visible — and to ensure that problems emerge before they become emergencies.
Understanding Kanban is relatively simple. The real difficulty lies in choosing the right materials, properly sizing the cards, and making the system work stably over time. These are precisely the steps where DIY implementations often get stuck.
For those who want to avoid the most common mistakes and get off to a solid start, Lean Factory School® propose the course Lean AdvancedA day in the classroom with simulations on a real physical product, where the Kanban system is designed, calculated, and tested directly on the field, according to the school's motto: Learn by doing.
In the Push logic, production is planned in advance based on forecasts: materials are pushed to downstream departments regardless of actual demand, often leading to high inventories, out-of-control WIP, and tied-up capital. The Pull logic works in reverse: no department produces or moves material until the downstream process explicitly requests it. The Kanban system is the operational tool that makes this Pull logic a reality, using physical or digital cards to trigger replenishment only when there is a real need.
There are three main variants of the Kanban system. The Kanban standard it is the most widespread: each container has an associated tag, and when it is emptied, the tag automatically becomes a restocking order. The Kanban batch size it works similarly, but the supplier waits for multiple tags to accumulate before starting production: this is indicated when the minimum production or purchase lot is larger than the quantity of a single container. The Kanban signal, instead, it reintroduces the reorder point logic: the signal is sent only after a certain number of containers have been consumed and is suitable for less regular consumption or larger supply batches.
The number of tags is obtained by dividing the total requirement to be covered (i.e., the average demand multiplied by the lead time, plus safety stock) by the standard quantity contained in each container. For example, with an average demand of 50 pieces/day, a lead time of 3 days, safety stock of 30 pieces, and containers of 25 pieces, the result is 8 tags. A fundamental aspect: if the lead time improves (e.g., drops from 3 to 2 days), the number of tags needed is reduced proportionally, making every process improvement visible and measurable.
Kanban works best for components with stable, predictable, and recurring consumption: screws, gaskets, connectors, bearings, and generally anything that is used frequently and in similar quantities. A good rule of thumb is that if a component is used in 80% of finished product SKUs with a reasonable lead time, Kanban is almost certainly the right choice. For expensive, model-specific components with long or unpredictable lead times, however, other policies such as MRP or dedicated supply agreements are preferable. For small, low-value items, there is also the ’empty-for-full“ method, a simplified version using only two containers.
Kanban is not an isolated tool, but the operational mechanism that brings Just In Time (JIT) to life: each department starts production only when it receives a demand signal from the downstream process, and this mechanism propagates backward along the entire chain to the suppliers. Within the system, the productive supermarket It is the controlled storage point where Kanban-managed materials are picked up and replenished. It is not a traditional warehouse but a precisely sized buffer that is self-managed through tags. Takt Time, which is the pace at which the market absorbs products, defines the speed of the entire system and, consequently, the number of tags needed to maintain flow without accumulating unnecessary inventory.
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