Kanban: Visual Signals That Control Production Flow

Kanban is a lean manufacturing visual control system that regulates production flow by signaling when to produce, what to produce, and how much to produce. The Japanese word means "signboard" or "visual card," and the Kanban system is the primary mechanism for implementing Just-in-Time production and pull systems on the shop floor. This manufacturing glossary entry explains Kanban mechanics, provides real-world results, and connects it to scheduling.

What Is Kanban?

Kanban is elegantly simple: nothing is produced or moved unless a signal authorizes it. The signal is typically a card, an empty bin, a marked floor space, or an electronic message. When a downstream process consumes material, a Kanban signal flows upstream to authorize replenishment of exactly the quantity consumed.

The system operates on six rules:

1. The downstream process withdraws only what it needs, when it needs it.
2. The upstream process produces only what has been withdrawn.
3. No items are produced or moved without a Kanban signal.
4. A Kanban card is always attached to the physical goods.
5. Defective products are never sent to the next process.
6. The number of Kanban cards is reduced over time to expose problems and drive improvement.

These rules create a self-regulating system that caps inventory at a predetermined level and prevents overproduction — the most damaging of the seven wastes identified in lean manufacturing.

How Kanban Works in Practice

The most common implementation uses two types of Kanban:

Production Kanban

Authorizes a work center to produce a specific quantity. When a container of parts is consumed by the next operation, the production Kanban card attached to that container returns to the producing work center, signaling it to make another container.

Withdrawal Kanban (Transport Kanban)

Authorizes the movement of material from a producing area to a consuming area. The downstream worker takes an empty bin and a withdrawal Kanban to the supermarket (a controlled inventory point), exchanges the empty bin for a full one, and attaches the withdrawal Kanban.

Kanban Sizing

The number of Kanban cards in the system determines the maximum inventory level. The formula accounts for demand rate, replenishment lead time, and a safety factor:

Kanbans = (Daily Demand x Lead Time x Safety Factor) / Container Quantity

Reducing the number of cards over time tightens the system, exposes problems (like long changeovers or unreliable equipment), and drives improvement.

Example with Numbers

An automotive parts supplier implemented Kanban for 120 high-volume part numbers that previously ran on MRP-generated batch production orders:

• WIP inventory dropped from $1.4M to $520K — a 63% reduction — because parts were produced only when consumed, not in large forecast-driven batches.
• Floor space recovered: 4,200 square feet of WIP staging areas were eliminated and converted to production use.
• Overproduction was virtually eliminated. Before Kanban, the shop regularly produced 15-20% more than needed "just in case." After Kanban, production matched consumption within 2%.
• Lead time for Kanban-controlled parts dropped from 10 days to 3 days because parts flowed through the shop continuously rather than waiting in batch queues.
• Stockouts decreased by 45% because the visual system made shortages visible immediately, unlike the MRP system where shortages sometimes went unnoticed until assembly.

Why Kanban Matters for Production Scheduling

Kanban and scheduling software serve complementary roles:

• Kanban simplifies execution for repetitive, high-volume items. Instead of generating and tracking individual production orders, the Kanban system self-regulates based on consumption. This frees the scheduler to focus on complex, low-volume, and custom orders.
• Reduced scheduling overhead: 120 Kanban-controlled part numbers represent 120 fewer items for production scheduling software like RMDB to sequence individually. The scheduler manages exceptions, not routine replenishment.
• Visual inventory control eliminates the gap between system inventory and actual inventory that plagues MRP-driven shops. What you see on the floor matches what the system says.
• WIP limits enforced by Kanban prevent work centers from being overloaded, which aligns with finite capacity scheduling principles.
• Hybrid systems work best: Many manufacturers use RMDB for make-to-order and complex jobs while using Kanban for repetitive components — combining the precision of finite scheduling with the simplicity of pull-based replenishment.

The lean manufacturing guide describes Kanban as the nervous system of a lean factory — carrying signals that coordinate the entire production flow.

Related Terms

• Pull System — The production philosophy that Kanban implements through visual signals and inventory caps.
• Just-in-Time — The broader production strategy that Kanban enables by synchronizing production with actual demand.
• Work-in-Progress (WIP) — The inventory between operations that Kanban directly controls and limits.

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See all lean and scheduling terms in the Manufacturing Glossary.