What is OEE?
OEE (Overall Equipment Effectiveness) is the one number that tells you how well a machine really runs. Here is what it means, how it is worked out, and where the lost time usually hides.
The formula
OEE = Availability × Performance × Quality
It answers one question: out of the time this machine was meant to be making parts, how much was spent making good parts at full speed? A machine that ran the whole planned time, at full speed, with no bad parts, scores 100%.
Availability: was it running?
Availability is the share of the planned time the machine was actually running.
Availability = Run time ÷ Planned production time
Planned production time is the time you meant to produce, such as an 8-hour shift minus a planned 30-minute break. Every unplanned stop, such as a breakdown, waiting for material or a long changeover, reduces it.
Performance: was it running at full speed?
Performance compares how many parts the machine made with how many it could have made at its ideal speed in the time it ran.
Performance = (Ideal cycle time × Total parts) ÷ Run time
The ideal cycle time is the fastest the machine is meant to make one part. Slow cycles and many tiny stops, too short to record one by one, reduce performance.
Quality: were the parts good?
Quality is the share of parts that were good first time.
Quality = Good parts ÷ Total parts
Scrap and parts that need rework reduce quality.
A worked example
These numbers are only an example, to show the arithmetic.
| Step | Example | Result |
|---|---|---|
| Planned production time | 8-hour shift minus 30-minute break | 450 min |
| Unplanned stops | Breakdown 25 min, waiting for material 20 min | 45 min |
| Run time | 450 − 45 | 405 min |
| Availability | 405 ÷ 450 | 90% |
| Ideal cycle time | One part every 30 seconds (0.5 min) | |
| Total parts made | Counted by the machine | 729 |
| Performance | (0.5 × 729) ÷ 405 | 90% |
| Good parts | 729 minus 22 rejects | 707 |
| Quality | 707 ÷ 729 | 97% |
| OEE | 0.90 × 0.90 × 0.97 | 79% |
Three numbers that each look fine on their own, around 90%, multiply to a much lower OEE. That is why OEE is useful: it shows how small losses add up.
The six big losses
Almost all lost time falls into six groups. Each one hits one part of OEE.
| Loss | Hits | Examples |
|---|---|---|
| Breakdowns | Availability | Motor failure, tool breakage, electrical fault |
| Setup and changeovers | Availability | Die change, product change, warm-up |
| Small stops | Performance | Jams, misfeeds, sensor blocked, short adjustments |
| Slow running | Performance | Running below ideal speed, worn parts |
| Start-up rejects | Quality | Scrap while the process settles after a start |
| Production rejects | Quality | Scrap and rework during steady running |
OEE for a line, a plant and a company
A line's OEE is not the average of its machines. On a line, the slowest machine (the bottleneck) sets the pace, so the line's output is what counts. At plant level, quality must be weighted by the number of units each line made; otherwise a small line with perfect quality can hide a big line's problems. Nisthora does this weighting for you.
Why OEE needs a work order
To work out performance you need to know what was being made, because each product has its own ideal cycle time. To work out availability you need to know when production was planned. That is why Nisthora ties machine data to work orders and batches, and counts it only while a batch is running.
How Nisthora measures OEE
- Run time comes from the machine's own run signal, read by Nisthora Edge.
- Part counts and rejects come from the machine's counters.
- Stop reasons are tapped by the operator on the machine panel.
- Planned time follows your production plan and shifts.
- Ideal cycle time is set per product and machine in master data.
See Nisthora on your own machines.
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