The three factors
- Availability: run time divided by planned time. It captures breakdowns, stops and changeovers.
- Performance: what was produced versus what would have been produced at rated speed in that time. It captures minor stops and slow running.
- Quality: good parts divided by total parts. It captures scrap and rework.
An example
A line has 8 planned hours and stops for 1 hour: 87.5% availability. In its 7 running hours it makes 3,150 parts, when rated speed would give 3,500: 90% performance. Of those, 3,087 are good: 98% quality.
OEE is 0.875 × 0.90 × 0.98, or 77%. Each factor looks acceptable on its own. Together they say almost a quarter of the planned time is lost.
What maintenance owns
Maintenance mostly drives availability, plus part of performance through minor stops. Quality also depends on raw materials and the process. That is why OEE is a plant metric, not just a maintenance one.
The usual mistake
Reporting OEE without saying which planned time it uses. Exclude scheduled stops, changeovers or shifts with no orders, and the same equipment jumps from 60% to 85% without anything changing. Before comparing two OEE figures, compare how they are calculated.