Key takeaway
OEE is useful only when each of its three losses is measured in minutes that someone can go and recover.
01One number, three losses
Overall Equipment Effectiveness multiplies three ratios: availability, performance and quality. Availability is the share of planned time the machine actually ran. Performance is how close the running time came to the ideal cycle. Quality is the share of parts that were good the first time.
The number itself is less important than the split. A plant at 75% OEE with a 90 / 85 / 98 split has a different problem from a plant at 75% with 96 / 79 / 99. The first is losing time to stops. The second is losing it inside the cycle.
02Availability: the stops you can see, and the ones you cannot
Long stops get reported. A two-hour breakdown will be on the shift sheet. What does not get reported is the five-minute wait for material, the three-minute inspection, the ninety-second tool touch-up. Across a shift these add up to more than the breakdown, and they never appear in a manual report.
Automatic capture changes this. Every state change is timestamped at the control. The operator adds a reason in two taps. The availability number becomes something that can be argued about in minutes, not opinions.
- Planned time excludes breaks and planned maintenance by definition
- Changeover counts against availability unless the plant decides otherwise, and the decision must be consistent
- Micro-stops under two minutes are usually the largest hidden loss
03Performance: slow is the new stopped
A machine running at 90% of its ideal cycle looks fine on the floor. The spindle turns, chips fly. But 10% of every cycle is being given away, and unlike a stop, it has no start and no end to notice.
The ideal cycle must be defined honestly. Use the best demonstrated cycle for that part on that machine, not the routing time in the ERP. A performance figure above 100% means the standard is wrong, not that the machine is heroic.
04Quality: count it at the source
Quality loss is often small in percentage and large in money, because a scrapped part has already consumed availability and performance. Scrap and rework should be recorded at the machine where they were detected, with the reason, so the loss lands on the right OEE.
05Reading the waterfall
Start with 100% of planned time. Subtract availability loss in minutes. From what remains, subtract performance loss. From what remains, subtract quality loss. What is left is OEE. Presented this way, every point has a number of minutes attached, and every minute has a reason. That is when OEE stops being a score and starts being a to-do list.