Quality Rate can not be determined immediately

Q:  Sometimes our process is being interrupted; i.e. the oven is stopped at a different moment than planned. At that moment it is not clear whether the product will be OK or not. We will block the product and take samples to determine the quality. This could take a couple of days. Wen everything is OK the product is released, otherwise it is being scrapped. This would have a retrospective effect on the OEE I guess? A correct OEE for the day is no longer possible in this way. What number should I now use?


Measure OEE for Batches

Q: Is it possible to use OEE in an intermitting production, when producing batches?

Arno Koch •     There are two problems in this question;

  1. How do I measure an accurate OEE when running batches
  2. Can I measure an OEE for each batch

I will answer the second question here;

The major goal of OEE is to identify whenever the machine is not running smoothly causing losses. In the situation, when a machine has to be stopped regularly (even when there seem to be ‘plausible reasons’), it makes sense to identify and quantify such reasons. This might reveal a new perspective to the ‘accepted’ equipment losses.

Losses do not only occur while running batches. A major part of the losses might occur between the batches. So we want to see those losses.

  • If you do not run between batches (ie because the line is not balanced) register “waiting for process X”.
  • If buffers are full register “No output due to buffer full” etc.
  • If demand is irregular register “waiting for production order”.

This will indicate where to focus your improvement efforts, being the main goal of OEE.

The problem would be: Are you going to assign such losses to a/the batch? Probably not since there is no correlation to that batch. So you would miss this loss…

So measuring OEE of batches only, could make you blind for a substantial part of the losses on the equipment. I would rather widen your timeframe where you measure OEE (in cases of long batch time). Instead of OEE per shift, consider an OEE per 24 Hr or per week. In this case you will keep all losses in the picture.

The question you should consider is this: If you measure OEE only during batch-time, what are you NOT measuring?
If the process is intermittent, I would like to know this! How often is it interrupted? How long? How much variance in the intervals? Here are many indicators; something strange is going on in the value stream.
Many batch processes run on capital equipment. Why is it not ‘batching’ all the time? Blinding out setups, preparation time, loading and unloading etc. etc. might bring you to wrong conclusions about what to improve in the equipment, the line or the value stream.

The point is: Beware of sub-optimization. While analyzing many hundreds pieces of equipment, I found out: Losses can be in complete other areas as usually searched for, or where you might expect them. The only way to find them is not to blind out any shelter where a loss might hide.

See also:

Performance goes over 100%…

Q: I’ve been having some difficulties in undestanding the definition to calculate OEE: from my experience, it should never be over 100%. However, by definition, performance can surpass 100%.

This will happen whenever the working center is turning faster than standard rate. In this case, should I take the actual cycle time instead of the standard one to limit the performance component at 100%? I need some help, please!