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* Best scores for use in calculation of best of best Figure 5.3 Equipment history record for OEE calculation

Potential improvement The first improvement objective is to obtain consistently, through standardization and stabilization, the best of the best in each of the three categories: availability, performance and quality. Beyond this point there must be continuous improvement towards world-class levels.

The OEE formula is as follows:

Overall equipment effectiveness availability of the asset performance rate when running quality rate of product produced

The three factors in the OEE calculation are all affected to various degrees by the six big losses which were outlined in Chapter 3 and are shown in Figure 5.4. It is only by a single-minded and sustained attack on these losses that the TPM process can become effective - a change that will be demonstrated by improvements in the OEE.

• Availability will be affected by breakdown losses and by set-up (or changeover) and adjustment losses. (A breakdown requires the presence of a maintenance engineer to correct it.)

• Performance will be affected by idling and minor stoppage losses and by reduced speed losses. (A minor stoppage can be corrected by the operator and is usually of less than 10 minutes' duration.)

• Quality will be affected by defect and rework losses and by start-up losses.

In detail, the calculation of the three factors whose product determines the OEE is as follows:

Availability total available time - actual downtime total available time

Total available time is total attendance time less downtime allowances (i.e. tea breaks, lunch breaks) and planned downtime. Unplanned downtime is caused by breakdowns and set-ups and changeovers.

Overall equipment effectiveness = Availability x Performance rate x Quality rate

Figure 5.4 OEE and the six losses

Figure 5.4 OEE and the six losses

Performance = operating speed rate x operating rate

Ideal cycle time actual cycle time x output

Actual cycle time operating time

Ideal cycle time is the cycle time the machine was designed to achieve at 100 per cent. Output is output including defects. Operating time is total available time minus unplanned stoppages (i.e. available time).

Quality total output - number of defects x 100%

total output

Off calculation for welding cell

Calculation of OEE can best be demonstrated by using the values in Figure 5.3. The roman numerals refer to the columns in the figure.

Average OEE calculation

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