What is Overall Equipment Effectiveness Score OEE and Why Does it Matter?
Machine Acceptance OEE (Overall Equipment Effectiveness) is the benchmark for measuring manufacturing productivity. Simply put – it identifies the percentage of manufacturing time that is truly productive. An OEE score of 100% means you are manufacturing only Good Parts, as fast as possible, with no Stop Time. In the language of OEE that means 100% Quality (only Good Parts), 100% Performance (as fast as possible), and 100% Availability (no Stop Time). It is extremely important that OEE is part of your User Requirement Specification (URS) at the beginning of your project so that your expectations are clearly laid out prior to Factory Acceptance Training (FAT’s).
OEE = Quality * Performance * Availability
Each of these key parts are taken into account when looking at OEE within a planned production time. The aim of the OEE is to discover any productivity and efficiency losses within a production time such as plant shut downs, lunch and break times etc. and taking steps towards mitigating these losses.
Quality relates to the quality of parts produced with the manufacturing process. Defects and rejects are parts which require rework so in order to obtain a 100% quality score the parts produced within the cycle would all be parts that are of perfect quality with no rework required.
Performance is all about time taken for parts to be produced. Minor stops and/ or slow cycles have an effect on the performance score. When running, the production process should be as fast as possible with no speed losses and an ideal cycle time to ensure a 100% score for performance.
Taking into account planned and unplanned stops, the availability score is that ratio of run time to the scheduled production time. If the production process is fully running when scheduled to do so this would indicate a 100% availability score.
For an Overall Equipment Effectiveness (OEE) score to be 100% then it could be said that the asset is not producing any waste parts, only high quality requiring no rework (100% quality), at a maximum speed (100% performance), with no stops or interruptions (100% availability).
The Six Big Losses
The most common losses for productivity within manufacturing can be found using what is known as The Six Big Losses. A main aim when looking at Overall Equipment Effectiveness (OEE) is to, as much as possible reduce these Six Big Losses and in turn increase efficiency and productivity.
The first part of availability lost is equipment failure and is related to lost time when the process cannot run because of failure. Bottlenecks in the production line, unplanned maintenance and breakdowns as well as lack of operators can lead to this.
Setup and Adjustments
Setup and adjustments are the second part which make up availability loss and are as a result in the time lost in production because of change over of parts, equipment and/or quality checks and inspections. Part cleaning and warm up time can also lead to this loss.
To improve overall equipment effectiveness (OEE) is it critical to reduce both equipment failure and setup stoppage time because they other OEE factors cant be improved when the manufacturing process is down.
Idling and Minor Stops
Idling and minor stops are categorised as a performance loss, as such stops are due to factors such as equipment jams, misalignment of parts, incorrect settings or quick alterations during a process. These stops are not usually predictable and are often considered part of normal operation, thus are commonly overlooked.
Reduced Speed accounts for time where equipment runs slower than the Ideal Cycle Time (the theoretical fastest possible time to manufacture one part). Another name for reduced speed is slow cycles. Reduced speed is a Performance Loss. This situation may occur due to incorrect control and operation of the equipment, inappropriate materials or worn-out tools.
Process Defects account for defective parts produced during stable production. This includes scrapped parts as well as parts that can be reworked, since OEE measures quality from a First Pass Yield perspective. Process defects are a Quality Loss.
Examples of common reasons for process defects include incorrect equipment settings, operator or equipment handling errors, and lot expiration (e.g., in pharmaceutical productions).
Classed as the second aspect of quality loss. Reduced yield is similar to process defects, however, reduced yield is produced during the beginning of production. That is, parts produced from the machine start-up to the point that steady-state operation is obtained. These parts may be waste/ scrap, or may need further work to reach the expected part quality. Reduced yield can be a result of inappropriate machine settings or the need for warmup cycles.
Using The Six Big Losses
Using the Six Big Losses framework creates a concrete path to improve your OEE score.
- Working to reduce Availability Loss in the form of Equipment Failures or Setups and Adjustments protects you against preventable unplanned stops or downtime, as well as minimises any planned stops.
- Addressing Performance Loss that results from Idling and Minor Stops, as well as Reduced Speed, prevents small stops and slow cycles from accumulating.
- Minimising Quality Loss in the form of Process Defects and Reduced Yield reduces the number of unusable parts produced before and during steady state production.
The Six Big Losses name and categorise problems that manufacturers face every day. Consistently working within this framework to take action, one loss at a time, will result in a consistently improving OEE score.
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