EPEI
Every Part Every Interval: how often a process can come back round to the same part. A capability derived from changeover time, not a target typed in.
Formula
In practice
EPEI — every part every interval — is reported as a capability, not a schedule. It is the shortest interval over which a process could cycle through its whole mix, given what changeovers cost it and what the day leaves after the run time demand requires. The interval a plant intends to run is a separate field, and the gap between the two is the size of the prize from reducing setup time. Keeping them apart is the only reason that gap is visible at all.
Where demand already consumes the day, there is no interval to report. The product publishes nothing rather than a large number, because what exists in that case is not a long interval but a deficit, and the capacity check is where a deficit belongs.
How this is calculated
EPEI = (products × changeover duration) / (net available − run time needed)
This is a capability, not a schedule: the shortest interval over which the
process could cycle through its mix. epeiTargetDays holds the policy. The
gap between them is the size of the prize from SMED, and it is only visible
because the two are separate. Undefined when demand already consumes the day —
then there is no interval, only a deficit that the capacity check reports.
Common questions
Is EPEI the interval we actually run?
No. It is the shortest one the process is capable of. What you intend to run is held separately as a target, and the report shows both — a process capable of every-part-every-two-days running on a two-week cycle is a finding, and it disappears if one figure overwrites the other.
Why is no EPEI shown for my process?
Because the run time demand requires already fills the available day, leaving no room to cycle through the mix. That is not an interval that happens to be long; it is a capacity shortfall, and it is reported as one.
This definition is the one the product itself shows, read from its interface catalogue at build time.