OEE - Overall Equipment Effectiveness

Topics covered in this article:

What is OEE?

Three Components of OEE

Calculating OEE for a Single Job on One Machine

Calculating OEE Across Multiple Machines  (Aggregated OEE)

Aggregated OEE Calculation Method

Reporting Tools for OEE

Definitions

What is OEE?

OEE is an acronym that stands for Overall Equipment Effectiveness and is a metric measures the overall efficiency of a machine or group of machines.  It is a valuable measure of a machine's performance that uses multiple components. 

*Please Note:  OEE only accounts for the time when jobs are scheduled and a job must be being run for OEE to work.  To learn more about jobs, please visit this article.

Three Components used to calculate OEE

There are three components that are used to calculate the OEE score as defined below:

Availability

Availability is how much time a machine is running vs the entire amount of time it was scheduled to be running.  A machine is considered to be running when the execution state of the machine is active, and what determines active varies by machine and control. 

For example:  If a machine is scheduled to run a job for 8 hours, and it is active for 4 of those 8 hours, the availability score for that machine will be 50%.

Performance  

Performance is a measure of the difference between the Ideal Cycle Time and the Actual Cycle Time. 

For example: If each part produced has an Ideal Cycle Time of 2 minutes, and the machine's Actual Cycle Time for each part is 2 minutes, the performance of the machine will be 100%. 

*Please Note:  This is the only OEE component that can be greater than 100%.

Quality

Quality refers to good parts vs bad parts, or how many total parts were produced and how many of those parts were considered good parts. 

For example: If a machine is running a scheduled job and produces 200 parts, 150 good parts, and 50 parts were rejected, the Quality will be 75%.

Calculating OEE for a single Job on One Machine

As outlined above, each of these three components produces a percentage.  The percentages are then multiplied, and the product becomes the OEE for that machine. 

OEE= Availability * Performance * Quality

For example: Using the percentages in the previous section, the OEE would be calculated as 37.5% (50% * 100% * 75%).

Calculating OEE Across Multiple Machines (Aggregated OEE)

The calculation is more complex when multiple machines are factored in because the components become different.  Making different parts with different cycle times, or machines running for a different amount of time will affect how the OEE score is calculated. 

Simply using the standard OEE calculation for an aggregated OEE calculation will not work. Here is an example:

Two machines making the same part - one runs for 30 minutes the other runs all day. The 30 minute run is at 50% OEE, but the all-day-run is at 100%. The aggregated OEE can’t possibly be 75%, which is the result you would get by simply averaging the OEE percentages from each machine.

As you can see in the example above, aggregated calculations for OEE must be weighted. 

Aggregated OEE Calculation Method 

To calculate the aggregated OEE, each component of OEE is weighted by both a factor unique to itself and a VALUE_FUNCTION that is shared by all the components. The unique factor is related to the nature of the component and combined, they preserve the OEE product invariant.

The VALUE_FUNCTION factor is any weighting factor from an individual item that is applied consistently to all three components. This factor can change the resulting availability, performance, and quality values that come out in aggregation, but will never affect the aggregate OEE value (it cancels out). Examples of value functions are ideal part time and part value. By default, MachineMetrics calculates OEE with ideal part time.

Weighted Availability 

The scheduledTime / idealPartTime weights availability by the number of parts it could theoretically produce over the scheduled time.

*Please Note: If VALUE_FUNCTION is idealPartTime, the expression simplifies to SUM(availability * scheduledTime).

Weighted Performance

aggPerformance = SUM(performance * ((scheduledTimeInCycle / idealPartTime) * VALUE_FUNCTION)) / SUM((scheduledTimeInCycle / idealPartTime) * VALUE_FUNCTION)

The scheduledTimeInCycle / idealPartTime weights performance by the number of parts it could theoretically produce over the scheduled time when it was actively executing.

*Please Note: If VALUE_FUNCTION is idealPartTime, the expression simplifies to SUM(performance * scheduledTimeInCycle).

Weighted Quality 

aggQuality = SUM(quality * (totalParts * VALUE_FUNCTION)) /
SUM(totalParts * VALUE_FUNCTION)

Overall Weighted OEE

aggOEE = aggAvailability * aggPerformance * aggQuality

Reporting Tools for OEE

To look at your own OEE report, there are two options.  The out-of-the-box OEE report, and the Report Builder, which is a more powerful and customizable tool that can be used to build reports.  For more information on how to build the OEE Report in the Report Builder please click here.

Definitions

• allTime - The queried range of time.
• nonOptionalTime - The amount of time over the queried range of time covered by shifts that are not considered optional (an example of an optional shift would be an overnight 'AP off' that is not normally staffed)
• scheduledTime - The amount of time that a machine has been scheduled to operate over the queried range of time.
• scheduledTimeInCycle - The amount of time a machine has been in cycle (executing) during its scheduled times.
• scheduledTotalParts - The amount of parts produced during a machine's scheduled times, excluding periods of planned setup.
• idealPartTime - Sometimes referred to as idealCycleTime, the theoretical shortest amount of time that a machine should be able to complete a part.
• totalParts - The total number of parts produced over the queried range of time.
• goodParts - The amount of totalParts that represent good parts.

Have Questions?

If you have additional questions about OEE please reach out to support@machinemetrics.com.