WHAT IS OVERALL EQUIPMENT EFFECTIVENESS?
Overall Equipment Effectiveness (OEE) is used to monitor manufacturing effectiveness.
The resulting OEE percentage is generic and allows comparisons across differing industries and processes.
OEE Availability is the ratio between the actual runtime and planned production time. The planned production time does not include breaks, lunches, and other pre-arranged time a production line or process may be down. Anytime equipment is not running when it was planned to be is an inefficiency that is reflected in the Availability.
If a line is run for one 8-hour shift with two 15-minute breaks and one 30-minute lunch, then the planned production 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 45 minutes of downtime, then the runtime is 6 hours, 15 minutes (derived from 7 hours of scheduled time – 45 minutes). The OEE Availability equals 89%, calculated from actual runtime divided by the scheduled runtime, or 6 hours, 15 minutes divided by 7 hours.
OEE Performance is the ratio between the actual number of units started (not the number that has been produced) and the number of units that theoretically can be processed based on the standard rate. The standard rate is the rate the equipment is designed for. Performance is not based on the number of units produced, but, on what the line was designed to process over a given period of time. If equipment is running slower than what it is capable of, then it is not as efficient as it could be and is reflected in Performance.
If a work cell is designed to process 10 units per minute, we can calculate the theoretical amount of units it can process in a given amount of time. Using the 6 hours, 15 minutes of actual runtime from the above example, a total of 3750 units would be processed (or started). Calculated from taking 6 hours, 15 minutes (375 minutes) times 10 units per minute. If the actual number of units processed is 3000, then OEE Performance is 80% (calculated by 3000 / 3750).
OEE Quality is the ratio between good units produced and the total units that were started. The inefficiency of out-of-spec units that could have been good units is reflected in Quality.
Taking the number of units produced from above of 3000, if 200 units were rejected at the quality inspection station, then 2800 good units are produced. The OEE Quality is 93% calculated from 2800 divided by 3000.
This is the final calculation that measures Overall Equipment Effectiveness and is a combination of all three OEE sub-values. It is important to know that the OEE sub-values are isolated from each other. If equipment is down, then only Availability is affected while Performance and Quality remain the same. If the equipment is running slow, then only Performance is affected while Availability and Quality remain the same, etc.
Using all the numbers from above, 89% x 80% x 93% = 66%.
This may seem like a low number but it is important to keep 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; however, using Sepasoft’s OEE Downtime and Scheduling module allows much more than just comparing OEE results between production runs. It allows you to compare OEE results between equipment, departments, facilities, operators, shifts, products, or other factors you define (e.g. raw material vendor, humidity, etc.).