Overall Equipment Effectiveness, OEE
Equipment is one of the most valuable assets of any manufacturing facility. Effective asset management assumes that production assets must work as long as possible with the maximum allowable utilization rates. That is, the equipment should not only be in working order but in good technical condition, which is achieved through regular preventive maintenance and systematic elimination of losses associated with equipment changeovers, loading raw materials, and other production processes. The Total Equipment Maintenance (TPM) concept helps to achieve these goals. It is important to understand what metrics help in assessing the availability of equipment for uninterrupted operation.
Overall equipment effectiveness (OEE) is an integrated measure of equipment performance designed to monitor and improve production efficiency, based on the measurement and processing of specific performance indicators.
The OEE indicator makes it possible to analyze productivity losses and identify problem areas of production. It allows you to get an answer to the most important question for an enterprise manager — how can you quickly and significantly increase output without increasing production capacity?
The OEE toolkit is widely used as key performance indicators (KPI), which, when combined with lean manufacturing technologies, allows an enterprise to increase its competitiveness.
- The OEE is calculated using the following formula
OEE = A * P * Q
where:
A — criterion of availability (availability) of equipment (Availability)
P — performance criterion (Performance)
Q — quality criterion (Quality).
Each of the three criteria is calculated using a separate formula. - Calculation of the criterion of availability
A = OT / PPT
Here
OT is the operating time, i.e. the time when the equipment actually worked and produced products.
PPT stands for planned production time or planned production time.
The operational time is defined as the difference between the planned PPT production time and the DTL unscheduled downtime loss:
OT = PPT — DTL
A distinction should be made between the time of unplanned DTL outages and the time of planned shutdowns (PSD), which is excluded from the effectiveness analysis.
The availability criterion analyzes stop loss (DTL), which includes any unplanned outages, such as equipment breakdowns and failures, stops due to a lack of raw materials or lack of storage space, etc. - Calculation of the performance criterion
P = (TP / OT) / IRR
Here
TP — production output (total pieces), i.e. the actual number of units produced during the operating time OT,
IRR — ideal run rate — the maximum amount of products theoretically produced per unit of time.
The performance criterion takes into account the losses associated with a decrease in the production rate SL (speed loss). The production speed can be reduced due to the wear and tear of equipment, the use of materials of poor quality, the influence of the human factor. - Calculation of the quality criterion:
Q = GP / TP
Here
GP — the number of good pieces released during the operating time OT,
TP is the total number of products (total pieces) produced during the operational time OT.
The quality criterion takes into account the losses associated with the low quality of the product (quality loss).
The global standards for these criteria are currently:
Availability 90%, Productivity 95%, Quality 99%, resulting in an OEE of 85%
In international practice, it is generally accepted that the OEE indicator
- of more than 75% is good.
- from 65% to 75% — satisfactory.
- less than 65% is bad.
The purpose of calculating the OEE is not to find out how far the company lags behind international standards, but to get closer to them. A one-off OEE calculation is not enough for this. It is necessary to find out at what stage of production the main losses occur, to take measures to eliminate them, and in the future to track the dynamics of changes in OEE, quickly finding out the reasons for its decrease and reacting to it just as quickly. This requires:
- in each work shift, record the time that the equipment is in working and non-working condition, as well as register the transitions from one to another.
when registering, indicate the reasons for these transitions. - register the number of products produced, the number of defects, the reasons for the appearance of defects for each shift
calculate the indicator with an appropriate sample of data so that you can compare work shifts, production lines, or sections by their contribution to the final OEE — by shifts, lines. - make calculations for different periods of production.
after corrective actions aimed at eliminating the causes of losses, monitor their effectiveness, that is, evaluate the new OEE value and conduct analysis in the required sections. - monitor OEE continuously.
All information should be accumulated, stored and available to the enterprise management for analysis in the form of histograms or graphs.
Calculation and monitoring of OEE using paper media and Excel spreadsheets are only possible for small businesses. For a large enterprise, this task can only be solved with the help of a corporate information system, which will ensure the creation of a single repository of OEE data for all involved persons — managers of different levels, production, and maintenance personnel.