Page 412 - Intro Predictive Maintenance

World-Class Maintenance 403

mance, and the quality rate. This allows all departments to be involved in determin-
ing equipment effectiveness. The formula could be expressed as:

Availability ¥ Performance Rate ¥ Quality Rate = OEE
The availability is the required availability minus the downtime, divided by the
required availability. Expressed as a formula, this would be:
Required Availibility - Downtime
¥100 = Availability
Required Availability
The required availability is the time production is to operate the equipment, minus the
miscellaneous planned downtime, such as breaks, scheduled lapses, meetings, and so
on. The downtime is the actual time the equipment is down for repairs or changeover.
This is also sometimes called breakdown downtime. The calculation gives the true
availability of the equipment. This number should be used in the effectiveness formula.
The goal for most companies is greater than 90 percent.

The performance rate is the ideal or design cycle time to produce the product multi-
plied by the output and divided by the operating time. This will give a performance
rate percentage. The formula is:

Design Cycle Time ¥ Output
¥100 = Performance Rate
Operating Time
The design cycle time or production output will be in a unit of production,
such as parts per hour. The output will be the total output for the given period. The
operating time will be the availability value from the previous formula. The result
will be a percentage of performance. This formula is useful for spotting capacity
reduction breakdowns. The goal for world-class companies is greater than 95 percent.
The quality rate is the production input into the process or equipment minus
the volume or number of quality defects divided by the production input. The formula
is:

Production Input - Quality Defects
¥100 = Quality Rate
Production Input
The product input is the unit of product being fed into the process or production cycle.
The quality defects are the amount of product that is below quality standards (not
rejected; there is a difference) after the process or production cycle is finished. The
formula is useful in spotting production-quality problems, even when the customer
accepts the poor-quality product. The goal for world-class companies is higher than
99 percent. Combining the total for these goals, it is seen that:

90% ¥ 95% ¥ 99% = 85%
To be able to compete for the national total productive maintenance (TPM) prize in
Japan, the equipment effectiveness must be greater than 85 percent. Unfortunately, the