OEE - Overall Equipment Effectiveness
OEE
uses measures of downtime and downtime reasons to evaluate whether production
is running at or near capacity. OEE
takes into account, at a minimum: Availability (of production capacity);
Performance rate (production speed); and quality performance (good product
produced). Theoretically, 100% therefore
means that we ran at rated speed with no defects for all the time
available. (Although, depending on the
math, it is theoretically possible to achieve 110% by running with no defects
at faster than rated speed for 100% of the available time!)
Proponents
of OEE say that OEE truly reduces complex production problems into simple,
intuitive presentation of information. It helps you systematically improve your
process with easy-to-obtain measurements.
While this is true, implementing and understanding what OEE is telling
you is not easy.
While the general formula for calculating OEE is simple multiplication: Availability
* Performance * Quality, the specific mathematics of determining each of those
intermediate variables are complex and every
organization has its own complexities, and in many cases, its own
formulae.
Conceptually
it seems fairly simple - we want our production lines to be running as close to
100% capacity as possible. On a simple
basis, if we capture total production time, each downtime event, its duration,
and its reason, we have enough to calculate a crude OEE - total uptime / total
available time. And this can be done at
a reasonable cost. OEE systems become
much more complex as various modifiers are applied for "reasonable" events such
as set up time, scheduled maintenance, planned idle time, breaks, changeovers,
etc. There are norms in various
industries, but no hard and fast rules.
This
is a key area where your want an enterprise oriented solution, and not
individual plant or departmental systems.
OEE can easily become a basis for compensation and it is absolutely
essential that all of the calculations be identical regardless of where they
are done. Depending on the mathematics
and assumptions, the same picture can be expressed as a 90%
utilization, or a 60% utilization!