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OEE (Overall Equipment Effectiveness), a Key Performance Indicator
OEE is a key indicator that provides both performance measurement and action plans for improvement. As such, OEE is an effective investigative tool.
Targeted improvement of OEE generally makes it possible to improve productivity, but it also frees up capacity while delaying investment in additional equipment or the replacement of machines deemed too inefficient.
To carry out precise improvements, TPM proposes an indicator which integrates all the components of the machine output. At its core, OEE is part of an approach to optimize the performance of the production tool. This approach tackles all forms of production loss: breakdowns, slowdowns, series changes, material shortages and non-quality.
To achieve this result, this approach relies on expert knowledge of an indicator. OEE requires an indicator to be stationed permanently at each machine so that it recognizes better than anyone what's operating correctly or incorrectly during production. Giving the indicator access to support services allows the production tool to improve and become more reliable, resulting in greater efficiency and profitability.
The percentage produced by OEE represents the proportion of time the machine produces good parts. Thus a production line with an OEE of 40% produces good parts for only 40% of the time it is in use. The remaining 60% are losses that must be tackled to reduce waste.
When examining the differences between actual production and planned production, we identify influential factors which need to be eliminated to increase productivity. Measuring productivity consists of comparing useful time with reference time such as:
The time required: OEE reflects the most efficient time required by equipment to produce a product.
OEE = useful time/time required or OEE = (number of good parts made x cycle time) / time required
Total time: the OEE reflects the use of investments in heavy means.
OEE = useful time / total time Or OEE = (number of good parts made x cycle time) / total time.
Several methods can be considered for recording production downtimes at a work center: manual, semi-automatic and automatic data entry.
The use of semi-automatic or automatic systems makes it possible to measure the actual speed of the machines to identify speed deviations.
Manual entry is the easiest and fastest way to record downtime. The operators fill in the records of all the data (production, time, defects.). The records are specific about downtime to enable a more targeted study to improve OEE. The data collected must then be re-entered into a computer system for operation.
Although this method is fast and inexpensive, it is tedious for operators, costly in terms of time (recording and processing) and the completeness and reliability of the records is difficult to guarantee.
Semi-automatic data entry
Semi-automatic entry relies on help to read bar codes, pre-programm buttons, record all collected data, and more. A more advanced level of semi-automatic entry offers automatic acquisition of the stop duration. In this instance, the operator only has to inform the cause of the stop and the authorization of the restart once the stop reason has been entered.
This method is more reliable and comfortable for the operator than manual input. However, its implementation requires a material investment and always requires a vigilant operator.
Automatic data entry
Automatic data entry is based on a "cookie" system directly reported or available on the machine. The reading system dialogues with the machine's computers (or PLCs) or reads the states of the various sensors placed judiciously. When this capture is done by adding sensors, it can be difficult to carry out in an exhaustive way, as not all of the information is accessible.
Heavy in terms of investment, this method can only be considered on highly automated machines where the capture of information is easy and where the measurement of the OEE is permanent over a long period.
A Key Indicator for Anomaly Management
The primary goal of OEE is financial savings. Indeed, when OEE goes from 40% to 80% (which is a frequent example), productivity doubles with equal staff and investment. This gain can avoid an investment in additional time and machinery. When OEE reaches 90%, malfunctions in the organization are very low and additional gains appear: no more urgent deliveries, no more emergency troubleshooting ("fireman" type intervention), and the elimination of customer troubleshooting actions.
The second advantage is organizational. The OEE optimization approach brings together the resources of a site on the means of production. The analysis of OEE losses highlights in a coherent way the actions that need to be undertaken to improve the means. This unifying aspect makes it possible to organize the site's human and technical resources in a more efficient manner. Both human and technical resources carry out a mission in coherence with each other.
OEE losses are often due to small slowdowns that reoccur frequently. This problem is not likely to interest the technical services, but the harmful impact does not escape the operator who is confronted with these issues on a daily basis. Also, through its strong staff involvement and its working methods, this OEE optimization approach ensures in-depth reliability of the production tool.
Understanding the Causes of OEE Losses
The OEE value indicates the level of performance achieved. The performance improvement staff is most interested in understanding what the 100% top-up is, i.e. the share of hazards responsible for losses or underperformance.
To determine the causes of underperformance, the share of non-quality can be checked and related problems can be addressed using a problem-solving methodology. The available data on downtimes are then evaluated and the causes of these time losses are checked.
Experience shows that most of the time we will find:
- Organizational problems: lack of parts or raw materials; absence or delays in personnel, sub-optimal planning, long series changes, etc.
- Shutdowns (planned or not): maintenance, supplies, changes of series, controls, etc.
- Power failures or defects: mechanical, electrical, hydraulic, etc.
- Micro-stops and rate slowdowns
To treat OEE losses, it is necessary to strike while the iron is hot by obtaining the support of all and quickly resolving all problems encountered. This dynamic is based on the generalization of a structured methodology, the Plan-Do-Check-Adjust (PDCA) continuous improvement cycle.