Formula for OEE calculation – diagnosing problems and fixing them
The Formula for OEE calculation is simple, but the ingredients that go into it decide whether you get a correct OEE value. Here is an explanation of the commonly encountered problems in OEE calculation, and the fixes for them.
Availability = (Running time / Available time)
Performance = (Real production / Theoretical production)
Quality = (Good products / Real production)
Formula for OEE = A x P x Q
Availability is a measure of how much time the machine was made available for production, after downtime losses like machine breakdown, setup change, no raw material, etc.
Performance is a measure of the quantity that has been produced compared to what could have been produced.
Quality is a measure of rejections.
Formula for OEE - parameters and their meaning
| Parameter | Includes | Excludes |
|---|---|---|
| A Available time |
Time when the machine is planned to run, based on advance planning. | Time when the machine is NOT planned to run: Non-working shifts, Holidays, Lunch breaks, Tea breaks, Downtime for preventive maintenance, Downtime for autonomous maintenance, Machine cleaning time. |
| B Running time |
Time when the machine is actually running and producing. This includes: 1. Cycle time – time between start and end of a part’s production. Standard time for part unloading and loading. |
Time when the machine is not running, for any reason whatsoever: Setup, Rework, Inspection, Tool change, Waiting for raw material, Time for part loading/unloading that exceeds the standard time allotted. |
| C Theoretical production |
No. of parts that should have been produced in the Running time, based on the standard cycle time and standard part inload-load time. | |
| D Real production |
Number of parts actually produced in the Running time. Includes rejected parts. | Reworked parts. |
| E Good products |
Parts of OK quality. If a part is reworked and OKed, it counts as 1 part. |
Calculating OEE – problems and fixes
Causes of wrong OEE, and fixes
| Cause | Solution |
|---|---|
| 1 – In the formula for OEE calculation, you have considered a holiday as a working day and added it in the available time. | Remove the holiday time from the Available time in the formula for OEE. |
| 2 – You have considered a non-working shift as a working shift. | Remove the non-working shifts time from the Available time. |
| 3 – Break times (lunch, tea) considered are wrong. The break times in the calculation are less than the actual. | Correct the break times. |
| 4 – You have not deducted some planned downtimes in the shift, like machine cleaning or morning meeting. | Remove the planned downtimes from the Available time. |
Availability is abnormally high
| Cause | Solution |
|---|---|
| 1 – In the formula for OEE calculation you have considered a working day with poor availability as a holiday and deducted the time from the available time. | Add the time to the Available time in the formula for OEE. |
| 2 – You have considered a working shift with poor availability as a non-working shift. | Add the time to the Available time. |
| 3 – Break times (lunch, tea) considered are wrong. The break times in the calculation are more than the actual. | Correct the break times considered in the Available time. |
| 4 – You have deducted break times from the available time, but the machine is working right through breaks. | Remove the break times so that the available time increases. |
| 5 – You have deducted some planned downtimes in the shift that do not actually exist. | Reverse the deduction in the Available time. |
Performance is abnormally low
| Cause | Solution |
|---|---|
| 1 – In the formula for OEE calculation, you have considered a value of standard cycle time that is less than the actual on the machine. | Use the correct value of standard cycle time corresponding to the part and operation number on the machine, in the calculation for OEE. |
| 2 – You have considered a value of standard part unload–load time that is less than the actual on the machine. | Use the correct value of standard cycle time, corresponding to the part and operation number on the machine. |
| 3 – The number of parts produced that you have considered in the OEE calculation is less than what has been actually produced. | Correct the number of parts produced. |
Performance is abnormally high
| Cause | Solution |
|---|---|
| 1 – In the formula for OEE, for Performance you have considered a value of standard cycle time that is less than the actual on the machine. | Use the correct value of standard cycle time corresponding to the part and operation number on the machine, in the calculation for OEE. |
| 2 – You have considered a value of standard part unload–load time that is less than the actual on the machine. | Use the correct value of standard cycle time, corresponding to the part and operation number on the machine. |
| 3 – The number of parts produced that you have considered in the OEE calculation is less than what has been actually produced. | Correct the number of parts produced. |
Quality is abnormally low
| Cause | Solution |
|---|---|
| 1 – The value of good parts produced in the formula for Quality is less than the actual, which means the rejections considered are more than the actual. | Correct the value of good parts produced. |
| 2 – The value of parts produced in the formula for Quality is more than the actual. | Correct the value of parts produced. |
Quality is abnormally high
| Cause | Solution |
|---|---|
| 1 – The value of good parts produced in the formula for Quality is less than the actual, which means the rejections considered are more than the actual. | Correct the value of good parts produced. |
| 2 – The value of parts produced in the formula for Quality is more than the actual. | Correct the value of parts produced. |
