Overall Equipment Effectiveness (OEE)
Roll planned-time losses, speed losses, and defects into a single OEE score with its three factors.
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The engineering
OEE compresses a machine's whole shift into one number by multiplying three loss categories: Availability (did it run when scheduled), Performance (did it run at rated speed), and Quality (did it make good parts). Because they multiply, a chain of three good-looking factors — 90% × 95% × 99% — still lands at 85%, and one weak link drags the whole score down.
The gotcha is the reference clock: OEE measures against planned production time, not the full calendar. Never enter a cycle time faster than the machine actually achieved, or Performance blows past 100% — that's the sign your 'ideal' rate is fiction. Nakajima's world-class benchmark is 85% (roughly 90/95/99); anything above 100% means a definition error, not a great day.
Where this math comes from
OEE grew out of Total Productive Maintenance at Nippondenso (a Toyota-group supplier) in the 1960s and 70s, where operators were made responsible for the machines they ran instead of a separate maintenance crew. Seiichi Nakajima, working with the Japan Institute of Plant Maintenance, formalized the metric to expose the 'six big losses' — breakdowns, setups, minor stops, speed loss, startup rejects, and process defects — in a way a shop floor could act on.
Nakajima's 1988 book Introduction to TPM carried OEE to Western manufacturers, along with the now-quoted 85% world-class target. The three-factor A×P×Q form is deliberately blunt: it refuses to let good availability hide bad quality, which is exactly why it stuck on the plant floor.
- 1971Nippondenso / JIPMTPM formalized on the shop floor, with equipment effectiveness as its scorecard.
- 1988Seiichi NakajimaIntroduction to TPM defines OEE = A·P·Q and the 85% world-class benchmark.
- 2000SEMI E79Semiconductor industry standardizes OEE definitions for fab equipment.
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