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Calculating OEE

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OEE Overall Equipment Effectiveness

OEE – Overall Equipment Effectiveness

Overall Equipment Effectiveness, or OEE, is a measure used to evaluate the losses in a production process.  It gives an indication of the utilisation of a manufacturing operation.

Calculating OEE

OEE is calculated by multiplying three factors together.  The three factors that are used in the OEE calculation are:

  • Availability
  • Performance
  • Quality

The OEE calculation then is shown below:

OEE = Availability x Performance x Quality


Availability

Availability is a measure of downtime in a process.  The numerator for availability is the actual time spent running the process.  The denominator for availability is the scheduled time that the process should run.  Dividing the numerator by the denominator gives a percentage of uptime for the process.  If no downtime has occurred then the actual time and scheduled time are the same.  Dividing one by the other in this case, gives an availability of 1 or 100%.

If the actual time is less than the scheduled time then availability will be less than 100%.  Reasons for availability to be less than 100% include:

  • Machine breakdown
  • Startup losses
  • Tooling changeovers
  • Material Unavailable
  • Operator Unavailable

Performance

Performance is a measure of speed in the process.  The numerator for performance is the number of actual units produced by the process.  The denominator for performance is the number of units expected based on the actual time that the process ran.  Dividing the numerator by the denominator gives a percentage of production against the designed production rate.  If the process has run according to the cycle time in the standard work, then the actual units and expected units will be the same.  Dividing one by the other in this case, gives a performance of 1 or 100%.

If the cycle time is not adhered to and less units are produced than expected, the performance will be less than 100%.  Conversely, if more units are produced than expected, the performance will be greater than 100%.  However, the latter would indicate that the cycle times used to determine the expected units are incorrect and need to be reviewed and updated.

Quality

Quality is a measure of the precision in a process.  The numerator for quality is the number of good units produced according to the design of the product.  The denominator for quality is the total number of units produced.  Dividing the numerator by the denominator gives a percentage of acceptable units for the process.  If no defects have been produced, then the good units and total units will be the same.  Dividing one by the other in this case, gives a quality of 1 or 100%.

If the number of good units is less than the total number produced, then quality will be less than 100%.  Reasons for quality to be less than 100% include:

  • Damage
  • Contamination
  • Loose or overtightened parts (Torque)
  • Leaks
  • Missing parts or components
  • Incorrect components fitted

OEE – Overall Equipment Effectiveness


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