What kanban delivers and what it requires
Kanban is not a cure-all. It is a replenishment control tool that works very well under certain conditions and fails under others. People who decide to implement it without knowing both sides tend to blame the method when the real problem is the choice of item.
This article takes stock: what you really gain, what gets in the way, and the situations in which the right answer is not to use it. For the basics of the method, read the practical guide to pull production. To calculate the cards, use kanban sizing.
The reading rule is simple: every benefit of kanban has a condition behind it. Without the condition, the benefit disappears.
The real benefits
The gains are concrete, but they come from the structure of the system, not from the card itself.
- An explicit limit on work in process. The number of cards is the ceiling. Nobody produces beyond it, so overproduction, the worst of the wastes according to Ohno, loses room to exist.
- Production tied to consumption. The customer process pulls. The internal supplier only produces what was withdrawn, without depending on a forecast.
- Visual control of the situation. Cards piling up at one point show that something stopped there, without a report.
- Decentralized decisions. The operator knows what to do by looking at the board. The scheduler no longer issues orders for each workstation.
- Less inventory and less floor space. With inventory limited, the space freed and the capital tied up both shrink.
- Exposed problems. When inventory is reduced, breakdowns, slow changeovers, and scrap come to light. This is the most valuable benefit and the least discussed.
The challenges that derail implementations
Five adverse conditions appear most often on the shop floor.
High demand variability
If consumption swings widely from one day to the next, the loop needs a large buffer to avoid part shortages. A large buffer means more cards and more inventory, which cancels part of the gain. The solution involves leveling production before pulling.
Large item mix
With hundreds of variants, keeping a supermarket of all of them turns into an enormous inventory. Each item requires its own set of cards and its own location. In this case, apply kanban only to high-runner items and handle the rest by production order.
Long batches and slow changeovers
If a tool changeover takes hours, the batch has to be large to compensate. A large batch means a card holding many parts and a slow loop. Before pulling, reduce setup with SMED.
Unstable supplier
Kanban assumes reliable replenishment. If the supplier delivers late or out of specification, the loop's inventory runs out and the line stops. The system does not create reliability, it depends on it.
Lack of discipline in the rules
A lost card, a part withdrawn without a card, production started early for comfort: each deviation erodes control. Without simple audits and present leadership, the board becomes decoration within a few weeks.
Table: benefit vs condition for it to exist
Use this table as a checklist before deciding. If the condition on the right does not exist, the benefit on the left will not come.
| Expected benefit | Required condition | If the condition is missing |
|---|---|---|
| Less work in process | Reasonably stable or leveled demand | Inventory rises to cover the fluctuation |
| Fast, predictable flow | Short, stable lead time in the supplier process | Too many cards and delays in the loop |
| Control without paperwork | Simple rules followed by everyone | Lost cards and withdrawals with no record |
| Safe replenishment | A supplier reliable in lead time and quality | Part shortages and line stoppages |
| Little overproduction | Small batches and short setup | Large batches hide the excess |
| Visible problems | A culture that fixes the cause instead of hiding it | Inventory is increased to hide the failure |
When not to use kanban
There are situations in which kanban is the wrong tool. Recognizing them avoids wear and tear and discredit for the program.
- One-off made-to-order products. If every order is different and never repeats, there is no regular consumption to pull. Use order-based scheduling.
- Sporadic, unpredictable demand. An item that ships once a quarter does not justify a supermarket or cards.
- Low-volume, high-value items. Minimum stock of expensive, rare parts is usually an inventory management decision, not a kanban one.
- A process without minimum stability. Frequent breakdowns and high scrap stop the loop. Stabilize first with TPM and quality at the source.
- One-off or engineering projects. Work that does not repeat does not form a replenishment flow.
For items with no regularity, production planning and control (PCP) with MRP usually serves better.
How to decide item by item
Do not decide for the whole plant. Decide item by item, with three questions:
- Is the item consumed every day or every week, in a predictable quantity?
- Does the supplier process have a short, stable replenishment time?
- Does the item take up enough space and capital to be worth controlling?
Three yes answers indicate a good candidate. One or two call for preparation first. None means the item should stay out of the system. It is common to run kanban for only part of the items and traditional scheduling for the rest, and that is the correct decision, not an implementation failure.
Next step
List the ten highest-consumption items in your area. For each one, answer the three questions from the previous section and mark the condition that is missing. Choose an item with three yes answers and start with it. The others get a preparation plan: level demand, reduce setup, or stabilize the supplier.
If you want a complete roadmap, see the article on how to implement kanban in production.
Frequently asked questions
What are the main benefits of kanban?
A limit on work in process, production tied to consumption, visual control, decentralized decisions, and exposure of problems that inventory used to hide.
What is the biggest challenge of kanban?
Maintaining discipline in the rules. Without it, cards get lost, withdrawals escape control, and the system loses its effect.
Does kanban work with a large product mix?
It works best for high-runner items. Rare items or items with many variants are better handled by order-based scheduling.
When should I not use kanban?
In one-off made-to-order production, sporadic demand, unstable processes, or with an unreliable supplier, without prior preparation.
Does kanban reduce inventory on its own?
No. It limits inventory to the number of cards, but the real gain depends on leveling demand, reducing setup, and stabilizing the process.
Keep studying
Sources
- OHNO, T. O Sistema Toyota de Produção: além da produção em larga escala. Porto Alegre: Bookman.
- MONDEN, Y. Toyota Production System: An Integrated Approach to Just-in-Time. CRC Press.
- Lean Enterprise Institute. Kanban. Lean Lexicon. https://www.lean.org/lexicon-terms/kanban/
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About the author
Lean Manufacturing & Behavioral Management Specialist
Over 20 years in the automotive and metalworking industries (GM and Dana), Lean Manufacturing practitioner since 2006. SENAI instructor and mentor in Brazil’s Brasil Mais Produtivo program, delivering consulting, training and audits for 50+ companies, combining quality, productivity and people development.
