Capacity planning and control

Overall equipment effectiveness = availability rate X performance (or speed) rate X quality rate.

Some of the reduction in available capacity is caused

• by time losses such as set-up and changeover losses (when the equipment or process is being prepared for its next activity),

• and breakdown failures when the machine is being repaired. 

Some capacity is lost through speed  losses 

• when equipment is idling (for example when it is temporarily waiting for work from another process)

• when equipment is being run below its optimum work rate.

Finally, not everything processed by a  piece of equipment will be error free. 

So some capacity is lost through quality  losses.

Taking the notation in Figure 11.5,

OEE = a x p x q

For equipment to operate effectively, it  needs to achieve high levels of performance  against all three of these dimensions.

Viewed in isolation, these individual metrics are important indicators of plant performance, but they do not give a complete picture of the machine’s overall effectiveness.

This can be understood only by looking  at the combined effect of the three  measures, calculated by multiplying the three  individual metrics together. 

All these losses to the OEE performance  can be expressed in terms of units  of time – the design cycle time  to produce one good part. 

So, a reject of one part has an  equivalent time loss. 

In effect, this means that an OEE  represents the valuable operating time as  a percentage of the design capacity.

WORKED EXAMPLE

In a typical seven-day period, the planning  department programs a particular machine to work for 150 hours – its loading time.