# Short & sweet: EPEI – Every Part Every Interval

EPEI is a concept from lean management. If a limited range of parts is manufactured on a system or a group of systems, the EPEI value indicates the shortest cycle time after which a manufactured part can be returned to the system.
To calculate the EPEI value, the average daily demand quantities of all parts that are run over the capacity under consideration are determined. Multiplying these required quantities by their cycle times gives the total daily production time required on the line. The difference between the total production time per day and the available plant capacity per day indicates the time available per day for setting up the production orders.

The sum of all set-up times for the different parts results in the total set-up time required to produce all the different parts once. If you now divide the required total set-up time by the capacity remaining for daily set-up, you obtain the EPEI value.

For example, an EPEI value of 3.5 days for 7 different parts means that a particular part can be taken onto the machine every 3.5 days.
Multiplying the daily required quantity of a part by the EPEI value gives the minimum production batch size with which a part must be run through the system under consideration so that the system capacity is sufficient for production and set-up.

Our tip:
The minimum production batch size resulting from the EPEI value is a key control variable in the calculation of economic batch sizes. If, in a group of parts under consideration that are run through a system, an economic batch size below the EPEI batch size results for individual parts, this can only be realized under the given capacity restrictions if a correspondingly larger batch size results for another part. Otherwise, the EPEI lot sizes must be run over the system.

When considering EPEI, it does not always make sense to produce all the parts that have to run through a system in every production cycle. The cheaper a part is and the more sporadic its requirements, the larger the production batch size should be. Certain parts may only be produced two to four times a year, while others, typically the racing parts, have to be produced regularly. In this case, it makes sense to include only the racing parts in the EPEI cycle.
If there is really no alternative capacity available on which the sporadic parts can be produced and if the production capacity cannot be temporarily increased, then in such a selective EPEI analysis the available daily production capacity must be reduced by the amount that would be calculatively required for the set-up and production of the sporadic parts, converted to the individual working day.

Further information on this topic can be found here:

#### Prof. Dr. Andreas Kemmner

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