What is OEE (overall equipment effectiveness)?

Availability is run time divided by planned production time; it drops with breakdowns, setups and waiting for material. Performance is actual output divided by what the machine should have produced in that run time at its ideal cycle time; it drops with slow cycles and minor stops. Quality is good parts divided by total parts; it drops with scrap and rework. Multiply the three and you have OEE. The figure matters less than the three factors, because each points at a different kind of loss and a different fix.

Take a press brake with an eight-hour shift and a 30-minute planned break, so 450 minutes of planned production time. It loses 60 minutes to a setup and a breakdown, leaving 390 minutes of run time: availability is 390 divided by 450, which is 86.7 percent. Its ideal cycle is one part a minute, so 390 parts were possible; it made 350: performance is 89.7 percent. Of those, 340 were good: quality is 97.1 percent. OEE is 0.867 times 0.897 times 0.971, about 75.5 percent. The numbers are illustrative, but the arithmetic is the whole method.

OEE is usually taught alongside the six big losses, which map onto the three factors and tell you where to look first. Breakdowns and setups eat planned time before a single part is made. Minor stops and reduced speed are the quiet losses: the machine looks busy but produces less than its cycle time allows. Rejects at start-up and in steady production cost the material and the time already spent on them.

• Breakdowns (availability)
• Setup and adjustment (availability)
• Minor stops and idling (performance)
• Reduced speed (performance)
• Start-up rejects (quality)
• Production rejects (quality)

You do not need sensors to start. For one bottleneck machine, record on the job card the planned time, the start and stop of each run, the reason for each stop, the count produced and the count rejected. A week of that gives a believable OEE and, more usefully, a list of stop reasons by minutes lost. Fix the biggest reason, measure again. Compare a machine with itself over time rather than with a published benchmark; an OEE of 85 percent is often cited as world class, but a shop's own trend is the number that drives decisions.