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    GlossaryFloor Operations

    Queue Buildup

    Definition

    Queue buildup is the accumulation of work-in-process in front of a work center when jobs arrive faster than the center can process them. It is the visible mechanism behind lengthening lead time and is self-reinforcing: a longer queue at one resource pushes downstream queues to grow as well, propagating delay through the routing.

    Why it matters

    Queue time is 70–90% of total lead time in most discrete shops. A small change in queue dynamics produces a large change in delivery performance. Most ERP schedules use a fixed standard queue time, which means the published lead time is correct only when the queue happens to match the standard — never on a busy week.

    Common failure mode

    The bottleneck queue grows from 4 hours to 36 hours over a week as rush jobs are inserted. The scheduling system continues to compute downstream start dates from the 4-hour standard. Every promise date in the next ten days is wrong by a day or more, and no one in the system sees it coming.

    How Skody approaches it

    Skody computes queue time from live work-in-process and replans downstream operations whenever the queue ahead of them changes meaningfully. The scheduler sees queue buildup forming and surfaces it as an at-risk signal hours before it becomes a delivery problem.

    Related terms

    Queue Time
    The time a job waits in front of a work center before it actually starts processing.
    Work-in-Process (WIP)
    All started but not-yet-completed work physically on the floor — money tied up in motion.
    Bottleneck
    The resource whose limited capacity governs the throughput of the whole factory.
    Schedule Instability
    When the schedule changes so often that the floor cannot rely on it.

    Questions

    Most often, over-release of work to a bottleneck. Less often, a sudden change in arrival rate (rush jobs) or a drop in processing rate (machine down, operator out).

    Synchronize releases to the bottleneck pace (drum-buffer-rope, CONWIP), and let the scheduler refuse releases that would push the queue past a defined limit.

    A small queue (1–2 hours) on the bottleneck protects against upstream variability. Beyond that, queue is pure lead-time inflation.

    See queue buildup in your shop

    Run the Production Clarity diagnostic and see which scheduling constraints are costing you OTD today.

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