Page 17 - Intro Predictive Maintenance

8 An Introduction to Predictive Maintenance

the new equipment throughout its life cycle, long-term costs will be mini-
mized. Low purchase prices do not necessarily mean low life-cycle costs.

Overall equipment effectiveness (OEE) is the benchmark used for TPM programs. The
OEE benchmark is established by measuring equipment performance. Measuring
equipment effectiveness must go beyond just the availability or machine uptime. It
must factor in all issues related to equipment performance. The formula for equip-
ment effectiveness must look at the availability, the rate of performance, and the
quality rate. This allows all departments to be involved in determining 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 Availability 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 the
like. 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 Japanese 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 is in a unit of production, such as parts
per hour. The output is the total output for the given time period. The operating time
is the availability value from the previous formula. The result is a percentage of per-
formance. This formula is useful for spotting capacity reduction breakdowns. The goal
for most Japanese 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