3 Factors That Define OEE
Track Equipment Availability, Equipment Performance & Production Quality
Equipment efficiency is not simply the ratio of machine run time and scheduled time. Look at the situation of a manufacturing line or process running at half speed with zero downtime. This is truly only 50% efficient. Or, what if 10% of the product being produced does not meet your minimum quality and must be reworked. This equates to 90% efficiency, which does not take in account the effort to rework or losses of raw material.
There are three factors, all represented as a percentage, taken into consideration for the final OEE result:
OEE Availability is the ratio between the actual run time and the scheduled run time. The scheduled run time does not include breaks, lunches and other pre-arranged time a production line or process may be down.
If a line is scheduled for one 8 hour shift with two 15 minute breaks and one 30 minute lunch, then the scheduled time is 7 hours. Determined from 8 hours – 15 minute break – 15 minute break – 30 minute lunch. If during the production run there are 25 downtime events totaling to 45 minutes of downtime, then the runtime is 6 hours and 15 minute. Derived from 7 hours of scheduled time – 45 minutes. The OEE Availability is 89% and is calculated by 6 hours 15 minutes divided by 7 hours.
OEE Performance is the ratio between the actual number of units produced and the number of unit that theoretically can be produced and is based on the standard rate. The standard rate is rate the equipment is designed for.
If a work cell is designed to produce 10 units per minute we can calculate the theoretical production it can produce. Taking the 6 hours and 15 minutes of actual run time for the above example, a total of 3750 units can be produced. Calculated by taking 6 hours and 15 minutes which is 375 minutes times 10. If the actual number of units produced is 3000, then the OEE Performance is 80% calculated by 3000 / 3750.
OEE Quality is the ratio between good units produced and the total units that were stated.
Taking the number of units produced from above of 3000, if 200 units were rejected at the quality inspection station, then 2,800 good units are produced. The OEE Quality is 93% calculated from 2,800 divided by 3,000.
The final OEE calculation = Availability x Performance x Quality
Using all the numbers from above, 89% x 80% x 93% = 66%. This may seam like a low number but it is important to kept in mind that the OEE is not to be compared to 100%. The OEE result from this production run is compared to other production runs. Sepasoft’s OEE Downtime Module allows much more that just comparing OEE results between production runs i.e, comparing OEE results between operators, viscosity, mechanics, products, raw material vendors and any user defined factor you can think of.