Q: Suppose I want to calculate OEE continuously during the running shift, in order to present the team an ongoing status, how should I calculate this, specially when the machine is not running? Does the OEE drop to zero?
What if the Availability has been 50% for last hour but the actual production has been zero? What do you do with the Performance number? Should it be equal to zero?
Arno Koch • OEE can be used for several purposes; although steering improvement is the core, it can also come in handy at forecasting the potential capacity or to show the progress on the line, assuming you will use the number rather as a compass than a scientific precise guideline.
OEE, by definition, is always related to a certain time-frame; usually a shift (ie 510 min), but it also can be calculated for a day, a week or any other time-frame.
If you want to present an ongoing OEE during a shift, there are basically 3 ways to proceed:
- Using a fixed time-frame of let’s say 1 hour: Calculating a ‘fresh’ OEE every hour; you would see 24 OEE’s during the day. So if there was no output that hour, there was no availability, so the OEE would be zero. This answers the second part of the question: You say the actual production was zero, so how can there be an availability of 50%? This, by definition, can not happen. (There is availability when there is output, regardless the speed and quality.)
- Expanding the time-frame as time elapses: Whenever you (re)calculate the OEE, take the elapsed amount of time as 100% (meaning after 47 minutes you will calculate the theoretical output for 47 minutes versus the actual output in those 47 minutes and so on). So if you start with a running machine, the OEE will start immediately high. OEE will drop down when the machine idles and climb again when it restarts running.
- Take the total shift duration as time-frame. At the start of the shift, the theoretical output for that shift is calculated. This can be done for every minute in the shift. You would see a growing ‘reference’-line. At the start there is no actual output so OEE is zero. Whenever there is output OEE will climb a bit, until the shift is done. The operator will see his OEE grow. He can now see his actual output against the reference line showing where he could have been when there would have been no losses.
A good OEE software makes it possible to measure each relavant time window and visualize the OEE as well as the associated losses in various ways.
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