The Potential Limitations in Your OEE Calculation With Regards to Rejected Parts  

One of the most important things to understand about your OEE score is that really, you’re talking about three distinct metrics that come together to give you the most complete picture possible regarding how your manufacturing is working and where it could be better.

An OEE score that hits that coveted 100% marker (don’t worry, nobody has an OEE score of 100%) means that you’re manufacturing only the highest quality parts, with near constant availability, as quickly as humanly possible.

But at the same time, depending on the nature of your own environment you may not actually be in a position to detect rejected parts during the initial manufacturing process. Sometimes, you don’t have this information until hours or even days after the fact. If that’s the case for you, does it suddenly mean that you can’t implement OEE across your own production lines?

No. Far from it. In fact, the situation is a lot more straightforward than you might think – you just need to keep a few key things in mind.

OEE and Rejected Parts: Breaking Things Down

In the event that the total number of rejected parts aren’t immediately obvious to you as the manufacturing process continues in real-time, there are a few key steps you can take.

Obviously, you could simply delay calculating your OEE score until all of the information is available to you. Most people don’t necessarily use OEE as a real-time metric anyway – they use it to break down performance over specific periods to see where opportunities for improvement really lay.

You could also simply calculate your OEE score based on the information you do have available to you – that is, availability and performance. Here, you wouldn’t be including quality at all because you won’t have that information quite yet. Since availability and performance are the two major factors that impact your production time anyway, it’s still a valuable way to see what about your current operations is working and, more importantly, what isn’t. You should be mindful of the fact that you’re not including quality in this, however, as you’re not really getting the “complete picture” that you otherwise would.

Finally, you could essentially choose to calculate your OEE score twice – once using only availability and performance information as outlined above, and then again once information about the total number of rejected parts rolls in. This means that your OEE score will “change” after you first calculate it, at least on paper. But at the same time, it can be very confusing to track where your performance losses really are so this method isn’t necessarily recommended.

Regardless of which option you choose, the key thing is to fully understand what your OEE score is trying to tell you. Provided that you understand the context surrounding that number and what contributed to it, you’ll be able to use it as a guidepost to make the best and most informed decisions possible in the moment.