Clarification of Answer by
denco-ga
on
28 Mar 2004 13:24 PST
Howdy teanman-ga,
Confusion on how to do the OEE calculation is exactly why many
organizations do not use it. That said, the two calculations
that you present just don't make any sense, as utilization is
just one way of figuring the availability of a machine.
Utilization = Availability
There is no problem with substituting the percentage of "real"
hours the machine is available (reliability) instead of using
the potential number of hours (24/7/365) the machine could be
used (utilization.) Indeed, many places calculate OEE that way.
Reliability = Availability
The Plant Maintenance Resource Center states it as plainly as it
can be.
http://www.plant-maintenance.com/articles/tpm_intro.shtml
"OEE ( Overall Equipment Efficiency ) : OEE = A ...
A - Availability of the machine. Availability is proportion of time
machine is actually available out of time it should be available."
As an example, if the machine is normally only used 8 hours a
day, then there is no problem with calculating the that machine's
availability as a percentage of the hours that the machine is
actually used during that 8 hour period. So, if that machine has
an actual running time of 6 hours out of the 8 hours that it
should have been available, then you have a 75% (.75) availability.
There are even differing methods of calculating "performance" (and
"quality," too!) as well, again some ways taking into account "real
world" numbers of what that machine can realistically produce versus
the possible maximum numbers of what the vendor says that machine can
produce. Machines are often ran at slower speeds than the "maximum"
so as to prevent jamming or undue stress on the machine.
Ultimately it doesn't matter which method is used to calculate
"availability" or "performance" or "quality" as long as you are
consistent in your method. You are just comparing one of your own
OEE numbers against another one of your OEE numbers from one point to
another, and not against any kind industry "standard" of some sort.
Regardless, the consistent formula of calculating OEE is:
Availability x Performance x Quality
Some people substitute "utilization" for "availability," but that
just confuses matters. Availability is the more accurate, and
more consistent, term.
Yes, I have seen the following web page:
http://www.maintenanceresources.com/referencelibrary/ezine/TPMimplementation.htm
Wherein it is stated:
"OEE = Availability x Uptime Utilisation x Process Performance x Quality Yield"
In this case they are using "Uptime Utilisation" to mean "idling /
engineering time" which is a different concept than when "utilization"
is used in the context of machine availability. All the more reason
to consistently use the term "availability" in the calculation.
The following article from the Maintenance Technology web site might
interest you, as it presents three(!) ways of calculating OEE.
http://www.mt-online.com/current/06-98mm.html
"Using the example, three methods of calculating OEE are shown. Note
that accurate OEE can be determined from theoretical cycle time, number
of good units, and scheduled time."
Back to your original question of whether "utilisation and performance"
are the same, again, they are different things, as utilization (more
correctly, availability) is the percentage of time the machine is in
actual use versus the amount of time it is open to use, and performance
is a measure of pieces made versus the number of pieces that could have
possibly been made with that machine.
Looking Forward, denco-ga - Google Answers Researcher
