Understanding Total Preventative Maintenance (TPM)

Total Preventative Maintenance or TPM is a set of techniques which ensures that each and every machine in the production process is always able to perform its required task. This is done by placing the emphasis on production operators being trained to handle routine maintenance on a regular basis – they feel empowered, with a shared responsibility for the equipment and it frees up engineers to be available for more specialised tasks.

The approach needs to be Total in that it requires the participation of all employees, not only those personnel on the line but managers, engineers and operators. Secondly, it seeks the total productivity of all the equipment by focusing on the elements which account for the usual major losses that occur to equipment; downtime, change over time, minor stops, speed losses, scrap and rework.

The principle of TPM is that operators complete routine maintenance activities such as lubricating, cleaning, tightening and inspecting equipment. It blurs the distinction between the roles of production and maintenance by empowering operators to help maintain their equipment.

Overall Equipment Effectiveness or OEE is a TPM measure as to how effectively equipment is being used. OEE is calculated using three elements; the availability rate, the performance rate and the quality rate.

Availability Rate – downtime losses from equipment failures and adjustments as a percentage of scheduled time

Performance Rate – operating speed losses; running at speeds lower than the design speeds and any stops that last a few seconds

Quality Rate – losses due to scrap and rework as a percentage of total parts run

These three elements are used to calculate OEE with the following formula:

What is considered a good OEE score?

An OEE score of 100% is perfect production: manufacturing only good parts, as fast as possible, with no stop time.
An OEE score of 85% is considered world class for discrete manufacturers. For many companies, it is a suitable long-term goal.
An OEE score of 60% is fairly typical for discrete manufacturers but indicates there is substantial room for improvement.
An OEE score of 40% is not at all uncommon for manufacturing companies that are just starting to track and improve their manufacturing performance. It is a low score and in most cases can be easily improved through straightforward measures (e.g. by tracking stop time reasons and addressing the largest sources of downtime – one at a time).