The OEE, Overall Equipment Effectiveness, a key performance indicator
The OEE is a key indicator whose analysis provides both performance measurement and action plans for improvement. As such, it is an effective investigative tool.
The implementation of a targeted approach to improving the OEE generally makes it possible to improve productivity. But also to free up capacity while delaying investment in additional equipment or the replacement of machines deemed too inefficient.
Explanation of the OEE, Overall Equipment Effectiveness
To know with precision the situation and to carry out improvement actions, the TPM proposes an indicator which integrates all the components of the machine output, the OEE. The OEE or Overall Equipment Effectiveness 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 bases its action on a strong involvement of the operating personal, permanently with the machines. He knows better than anyone what's right or wrong. By giving it the means to involve the support services on the problems it has, the production tool can only improve, become more reliable, so more efficient and more profitable.
The OEE expressed in % represents the proportion of time the machine produces good parts. Thus a production line with a OEE of 40% produces parts that are good for the customer only 40% of the time it is used. The other 60% are losses that must be tackled in order to reduce or even eliminate them.
The search for the causes of productivity losses, i.e. differences between actual production and planned production, leads to the identification of influential factors. To increase productivity, it is therefore necessary to reduce all losses linked to these various non-productive factors. Productivity measurement consists of comparing useful time with a reference time such as:
The time required: the OEE reflects the use of means when they are used to produce.
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 and so to identify speed deviations.
- Manual entry
Manual entry is the easiest and fastest way to do this. The operators fill in the records of all the data (production, time, defects...). They are specific to downtime with a view to a targeted study to improve OEE. The data collected must then be re-entered into a computer system for operation.
Although this method is fast, inexpensive in terms of investment, 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 consists of a help for entering causes which can be carried out by reading bar codes, pre-programmed buttons, a specific keyboard, etc. A more advanced level of semi-automatic entry is the automatic acquisition of the duration of the stop, the operator only informing the cause of the stop and the authorisation 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 the rigour of the operators.
- Automatic data entry
Automatic data entry is based on a "cookie" system directly available on the machine or reported. 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, all the information not always being 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 the OEE is financial. Indeed, when the OEE goes from 40% to 80% (which is a frequent example), productivity doubles with equal staff and investment. This gain can avoid an investment. When the 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), 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 to be undertaken to improve the means. This unifying aspect makes it possible to better organize the site's human and technical resources. Each ensures its mission in coherence with the others.
OEE losses are often due to small slowdowns that recur frequently. This problem is not likely to interest the technical services spontaneously. On the other hand, their harmful impact does not escape the operator who is confronted with them 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. What the performance improvement staff is most interested in is the 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:
- Organisational problems: lack of parts or raw materials; absence or delays in personnel, sub-optimal planning, long series changes...
- Shutdowns (planned or not): maintenance, supplies, changes of series, controls...
- Power failures or defects: mechanical, electrical, hydraulic...
- Micro-stops and rate slowdowns
To treat OEE losses, it is necessary to obtain the support of all and quickly resolve all problems encountered, it is imperative to strike while the iron is hot. This dynamic is based on the generalization of a structured methodology, the "PDCA" continuous improvement cycle.