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Cycle Time Tutorial Definitions

Bottleneck

The machine group in a factory that has the highest loading for a given product mix. Some authors define bottleneck as having a loading of 100%. However, in common use, bottleneck usually refers to the most highly loaded machine group. 

Capacity

The maximum throughput of a factory or workstation. For a factory, the capacity is the throughput rate that drives the idle time on the bottleneck to zero.

Cycle Time

The total time required to produce a product, from entering the factory to leaving the factory. Cycle time includes time actually spent processing, as well as transport time and time spent waiting in queue. Cycle times by operation are also sometimes reported, and include the time from arrival at the operation until completion of processing.

Cycle-Time-Constrained Capacity

The throughput rate for a factory at which the average cycle time is equal to some target amount, usually expressed as a multiple of the total weighted average raw process time of the factory. For example, the 3X cycle-time-constrained capacity is the throughput rate at which the weighted average cycle time for the factory is no more than three times the weighted average raw processing time. 

Little’s Law

A fundamental relationship derived by J. D. C. Little concerning cycle time, work-in-process and throughput. Little’s Law states that at a given WIP level, the ratio of WIP to cycle time equals throughput. An illustration is available as part of this tutorial.

Throughput

The average output rate of a factory or workstation. The throughput of a factory is equal to the factory start rate multiplied by average line yield.

Work-in-Process (WIP)

The average number of units of product in the factory (or at a workstation). WIP includes units being processed on equipment, as well as units in transit, or awaiting processing at an equipment group.