Sequential pull

A pull system in which an upstream process only begins production when a downstream process requests a specific item, and in which production takes place in the exact order in which those items are requested. No inventory is held in a supermarket between process steps; the signal from the customer or the next process directly determines what is produced and when.

Sequential pull versus supermarket pull
‍In Lean , three types of pull systems Lean distinguished: supermarket pull, sequential pull, and mixed pull. In supermarket pull, an upstream process maintains a fixed buffer stock from which the downstream process draws; what is consumed is replenished. Sequential pull works differently: there is no intermediate inventory. The downstream process places a specific order in a specific sequence, and the upstream process produces exactly that, in that sequence.

Sequential pull is particularly well-suited when products are too diverse, too large, or too expensive to keep as buffer stock. In such cases, a supermarket would cause more problems than it solves: too many variants, too high a capital outlay, and too great a risk of obsolete or incorrect inventory.

Example: Automobile Assembly
‍Theclassic example is the automobile assembly line. Each car has a unique combination of color, engine, equipment, and options; it is impractical to maintain a buffer stock for every variant. Instead, each workstation sends a signal to the previous station to deliver the next part in the exact order in which the cars move down the line. The production of upstream parts, such as seats or dashboards, is coordinated with that specific order. This ensures that the exact right part is delivered at the right time, even without intermediate inventory.

Requirements ‍Sequentialpull places high demands on the reliability of the entire system. Because there is no buffer stock to absorb disruptions, delivery times must be predictable, quality must be assured, and the order sequence must be stable enough to enable timely control of upstream processes. Where that stability is lacking, a hybrid system—combining sequential pull and supermarket pull—is often a better choice.

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