Kanban System
Use simple visual signals attached to goods to pull production through the system, making overproduction impossible and waste visible
Kanban is the operational tool that makes Just-In-Time production work. In its most common form, it is a piece of paper in a rectangular vinyl envelope that carries three categories of information: pickup information, transfer information, and production information. Kanban circulates between processes, functioning as a withdrawal order, a conveyance or delivery order, and a work order. The system has six rules: the later process goes to the earlier process to pick up products; the earlier process produces only the amount withdrawn; nothing is picked up or produced without a kanban; a kanban must be attached to the goods; 100 percent defect-free products are required; and the number of kanban should be continuously reduced. When these rules are faithfully practiced, kanban controls the entire flow of production, prevents overproduction, makes defects immediately visible, and drives continuous improvement.
- Kanban is a tool for achieving just-in-time; its purpose is JIT, not the other way around
- The later process goes to the earlier process to pick up products; never push production forward
- The earlier process produces only the amount withdrawn by the later process
- Nothing is picked up or produced without a kanban; overproduction is structurally prevented
- A kanban must always be attached to the goods; it is the essential communication tool
- Defect-free production is required; do not send anything defective to the subsequent process
- The number of kanban should be continuously reduced, which drives down inventory and exposes problems
- Kanban makes the autonomic nervous system of production possible, enabling decentralized decision-making
- Establish Production Flow FirstBefore introducing kanban, ensure that production processes flow in the actual sequence of manufacturing. If machines are still clustered by function rather than arranged in process sequence, kanban cannot work. The production line must be set up so that work flows continuously before you add the signaling system on top of it.Pro tipToyota spent years establishing flow and teaching cooperating firms the Toyota production method before introducing kanban. Unless production flow is established, going straight to kanban will fail.WarningIntroducing kanban without first practicing the six rules and establishing flow brings a hundred harms and not a single gain.
- Design and Deploy Withdrawal and Production KanbanCreate simple, visual kanban cards that carry pickup, transfer, and production information. A withdrawal kanban authorizes the later process to go to the earlier process and pick up parts. A production kanban tells the earlier process to produce the quantity just withdrawn. Place kanban in clear vinyl envelopes attached to the goods they represent.Pro tipThe carrying cart itself can function as a kanban. When the standard number of engines at the assembly line is reached, the worker takes the empty cart to the engine assembly point and picks up a loaded cart. Overproduction is automatically checked because there is nowhere to put surplus units.
- Enforce the Six Rules StrictlyImplement and enforce all six rules simultaneously: (1) later process picks up from earlier process, (2) earlier process produces only quantity withdrawn, (3) no pickup or production without kanban, (4) kanban always attached to goods, (5) 100 percent defect-free requirement, (6) continuously reduce the number of kanban. Half-hearted implementation undermines the entire system.Pro tipRule six, reducing the number of kanban, is the engine of continuous improvement. Each reduction in kanban lowers inventory and exposes the next layer of problems to solve.WarningA kanban system used improperly can cause a variety of problems. If used to pick up parts from outside suppliers without first changing internal production methods, kanban becomes a dangerous weapon.
- Expand Gradually Through the OrganizationStart kanban within processes you directly control, prove it works, then expand to adjacent processes. Eventually extend to the full company and then to outside cooperating firms. At each stage, teach people by showing the system in action, not just explaining it theoretically.Pro tipOhno started in his own machine shop, expanded when he became plant manager, and achieved company-wide adoption only when he managed the main plant with authority over forging and casting. Use your growing authority to expand systematically.WarningIt took Toyota 10 years to establish kanban company-wide. Do not expect rapid adoption; the system breaks in new concepts that require time for everyone to understand and practice.
Starting in the machine shop around 1953, Ohno gradually expanded kanban through Toyota. He could only apply it within his own authority at first. When he managed the Motomachi plant in 1959, he extended it to the machine shop, press shop, and assembly line. In 1962, as main plant manager, he implemented it in forging and casting, making it company-wide at last.
Propeller shaft balance weights come in five types with highly irregular usage patterns. Traditional planning could not predict how many of each type would be needed, leading to either urgent shortages or excess inventory. Toyota attached kanban to the actual balance weights so types and quantities could be identified accurately at all times.
Ohno got the idea from American supermarkets, where customers get what they need, when they need it, in the amount they need. He connected the supermarket restocking method to production: the later process (customer) goes to the earlier process (supermarket) to acquire required parts at the time and in the quantity needed, and the earlier process immediately produces the quantity just taken, like restocking shelves. In 1953, Toyota applied this system in its machine shop using pieces of paper listing part numbers and machining information, which they called kanban (sign board). It took from 1953 to 1962 to implement kanban company-wide at Toyota, requiring every level of the organization to understand the system. The process was gradual, experimental, and met with considerable resistance, but Ohno expanded it steadily using his growing authority within the company.