OEE, or overall equipment effectiveness, is a calculation used by in manufacturing to gain visibility and improve inefficiencies in the manufacturing process. The calculation is composed of three factors:

OEE = Availability x Performance x Quality
OEE is part of the lean manufacturing approach. It's objectives are to continuously improve operating margins and maximize the use of resources. OEE analysis starts with plant operating time, or the amount of time a plant is available for operation. From plant operating time, you subtract planned shut down, which includes any events that should not be included in efficiency analysis. (Events such as breaks, scheduled maintenance, or periods when there is nothing to produce). The remaining time is considered planned production time.

OEE begins with planned production time and scrutinizes efficiency and productivity losses that occur, with the goal of reducing or eliminating these losses. There are three categories of loss to consider. Downtime, speed loss and quality loss. Availability
Availability takes into account downtime. Examples of downtime include equipment failures, material shortages, and changeover time. Changeover time is considered a form of down time. It may not be possible to eliminate changeover time, but in many cases it can be reduced. The remaining available time is called operating time.

Performance
Performance takes into account speed loss, which includes any factors that cause the process to operate at less than the maximum possible speed, while running. Examples include machine wear, substandard materials, misfeeds, and operator inefficiency. The remaining available time is called net operating time.

Quality

Quality takes into account quality losses, which account for produced pieces that do not meet quality standards, including pieces that may be reworked. The remaining time is called fully productive time. The goal is to maximize fully productive time.

The concepts of OEE are simple and really help manufacturers focus on the underlying causes of productivity loss. The following are some common causes of loss, and reduced OEE. Downtime losses can be due to tooling failures, general breakdowns, setup, unplanned maintenance, change over, operator shortagesm material shortages and warm-up time. Speed losses can be due to rough running, component jams, sensor blocks, delivery blocks, misfeeds, cleaning, checking, under design capacity, under nameplate capacity, equipment wear and operator inefficiency. Quality losses can be due to in process damage, in process expiration, incorrect assembly, rejects during warm up, start up or production.

Eliminating unplanned down time is critical to improving OEE. Other OEE factors cannot be addressed if the process is down. It is not only important to know how much downtime your process is experiencing (and when) but also to be able to attribute the lost time to the specific source or reason for the loss (tabulated through reason codes). With downtime and reason code data available, analysis can begin starting with the most severe loss categories. Successful implementation of an OEE measurement system relies heavily on the existence of a complete and timely dataset. For effective use of an OEE management strategy, some thought needs to be directed at data availability and its sources.

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