Kanban is a core component of lean manufacturing, designed to manage the flow of work, optimize inventory, and enhance operational efficiency. The system manages complex production processes by limiting excess inventory and focusing resources on immediate needs. Its effectiveness hinges on establishing a clear, controlled mechanism for initiating work, which relies entirely on a specific signal to grant the authority for production to begin.
Understanding the Fundamental Difference: Push vs. Pull Systems
The concept of production authority is defined by the difference between push and pull manufacturing systems. A push system initiates work based on forecasts, anticipating future demand regardless of current capacity. This “make-to-stock” approach often results in excess inventory buildup and waste if the forecast proves inaccurate. A pull system, conversely, is reactive, initiating production only when demand is registered by the subsequent process or the final customer. This “make-to-order” structure ensures no material is created until the next stage is ready to receive it, meaning actual consumption dictates the pace of work.
Defining the Kanban Pull System
Kanban, which translates from Japanese as “visual signal” or “card,” is the mechanism used to implement the pull philosophy. It acts as a scheduling and inventory control system, providing a visual representation of the workflow and communicating demand across different stages. The system strictly enforces limits on the amount of Work-In-Process (WIP) inventory allowed between processes. By setting an upper limit on WIP, Kanban prevents bottlenecks and ensures resources are not tied up in unneeded products. The system uses visual cues, such as cards or empty spaces, to match production capacity precisely to the rate of consumption, regulating the system’s speed and inventory levels.
The Source of Production Authority
The authority to produce in a Kanban pull system originates from the consumption of material by a downstream process, not from a central plan. This consumption creates an inventory gap, which is the precise moment the system grants permission to replenish. The signal communicating this realized demand upstream is the definitive source of production authority. This signal is often a returned Kanban card or an empty container, representing the exact amount of material that must be replaced. Two primary types of signals govern this process: the withdrawal Kanban, which authorizes the movement of parts from storage, and the production Kanban, which authorizes an upstream work center to build the consumed items.
The Mechanics of the Kanban Signal
The authorization process follows a structured, cyclical path known as the Kanban loop. The loop begins when the downstream process consumes the material in a designated container. Once empty, the associated withdrawal Kanban card is sent upstream, authorizing a material handler to move a full container of replacement parts from the storage area (supermarket). When the full container is taken, the attached production Kanban is removed and sent to the upstream supplying process. This production card acts as the explicit work order, instructing the supplier to produce only the specified type and quantity, completing the cycle.
Benefits of Demand-Driven Production Authority
Adopting a demand-driven production authority structure provides significant operational advantages rooted in waste reduction. By ensuring nothing is made without a direct signal, the system actively prevents overproduction. This tight control drastically reduces the need for large buffer stocks, lowering inventory holding costs and minimizing obsolescence risk. Synchronization between processes improves, as each stage operates in direct response to the actual needs of the next, leading to a smoother, more predictable workflow. The immediate feedback loop increases responsiveness to changes in customer demand, allowing organizations to maintain high efficiency and flexibility.