OEE Overall Equipment Effectiveness

Overall equipment effectiveness (OEE) is a major part of any total productive maintenance (TPM) program implemented as part of Lean Manufacturing or six Sigma. OEE is a simple performance measure that reflects the health and efficiency of individual machines or processes.

OEE is a percentage figure calculated from three measures of how your machines or processes run; Availability, performance and quality. Note; it is only relevant for one machine or process, multiplying the figure across a plant or series of machines is meaningless.

These three measures are based on the six big losses of TPM and are detailed within the following sections.

Availability is the number of minutes within the working shift that the machine is available to work. The losses that can occur are due to your breakdowns and through your changeovers;

Changeovers

These are the losses in minutes due to setups and adjustments within your process, a setup being the time taken to go from the last good part of one product to the first good part of the next product.

Even when you have achieved the first good part of the next product you may not have achieved full production speed and any adjustments here causing lost time should be recorded also.

Breakdowns

These are unplanned stoppages taking more than 10 minutes (usually) and are due to mechanical (electrical, pneumatic, hydraulic, etc.) failure of some description The time taken to repair and get back to work should be recorded.

Example

You may have an 8 hour shift which is 8x60 = 480 minutes

Your changeovers may have taken 40 minutes and your breakdowns an additional 20 minutes for a total of 60 Minutes.

Your availability then is 480-60 / 480 or 88%

The machines performance is the actual speed vs what should be expected, normally measured in terms of output. So if you have 400 minutes of available working time and the cycle time is 1 minute then you should have 400 products, however we often experience losses in output due to running at reduced speeds or because of minor stoppages;

Minor Stoppages

These minor stoppages are often the most significant loss of productivity within your working shift, these are often difficult to measure exactly as they are frequent and take only a short period of time (less than 10 minutes.) These should be recorded on tally charts to gain an understanding of where your lost time is occurring. Typically these minor stoppages are things like clearing waste, changing tools, jams and similar minor problems and adjustments.

Reduced Speed

We also often find that we have machines running at less than design speed due to a host of issues such as worn machinery, incorrect setups and so forth.

Example

If you have a 30 second cycle time and you produced 800 parts in an available 420 minutes then your performace would be; 800 / (420 x 2) = 95%

Quality for OEE is a ratio of good parts produced compared to total number of parts produced; that is good parts plus all defectives.

Defects

Defects are any parts that do not meet the required specifications for the process / product and could be due to a host of reasons. Use of root cause analysis tools such as the 5 whys should be used to try to eliminate the causes of defects.

Setup scrap

The unusable parts created during the setup process are also recorded within your quality calculation for OEE.

Example

If you produced a total of 800 parts in the shift but 100 of these were defective your quality percentage would be 700 / 800 = 88%

Your OEE is calculated from your 3 measures above; Availability x Performance x Quality as a percentage.

So using the examples above our OEE calculation would be 88% x 95% x 88% = 74%

OEE (Overall equipment efficiency) like any other measure of performance is only of any value if we act on what we learn from it. OEE should be recorded graphically and the graph kept at the machine along with graphs showing the individual elements that constitute its makeup.

Kept at the workplace along with fishbone diagrams mapping out various causes of loss and action sheets recording what is being done to eliminate the various problems you can focus attention on improving your OEE.

These charts and action sheets should be the focus of regular shop floor meetings to drive continuous improvement.

Many performance measures can cause behavior that improves the measure but does not enhance the service to your customer; OEE is no different.

Focusing on improving OEE can cause behavior that prevents the wrong parts from being produced rather than those scheduled, the cell producing those parts that are easier to produce rather than what the customer really wants. A measure of schedule attainment should also be kept or you may fall foul of this problem.

OEE should be improved through setup reduction using tools such as SMED and through eliminating minor stoppages using the seven quality tools; not through running larger batches and reducing the number of changeovers that are completed.

Operators may not want to run products that have historically higher defect rates as it will harm their OEE figure!