Image: Sample illustration
Availability is a percentage indicator. It describes the extent to which a machine’s capacity is used for value-adding functions in relation to its planned availability. It is calculated as the ratio of the actual production time to the planned busy time.
The planned operating time results from the total reference period (e.g., one calendar week) minus non-production periods (e.g., weekends) and scheduled downtimes (e.g., routine cleaning and machine maintenance).
To determine the main operating time, actual stoppages, breakdown-related interruptions and the actual setup time are deducted from the planned operating time; the main operating time is therefore an actual time, i.e., one measured in reality, which makes it crucial for an accurate OEE calculation to record this time as precisely and immediately as possible. As mentioned above, availability is obtained as a percentage by dividing the main operating time by the planned operating time.
Availability =
Planned Operating Time
From this formula it follows that availability must always refer to a specific time interval. It is generated periodically and on demand. Values range from 0 % up to a maximum of 100 %. The larger the number—meaning the higher the utilisation of the machine relative to the planned time—the better. In the context of OEE, availability is also called the utilisation rate and forms the third factor, alongside performance and quality rate, in the equation. Availability, like the OEE derived from it, is relevant for shop-floor operators, plant management and executive leadership, because OEE is widely accepted as the benchmark and key indicator of an industrial facility’s productivity.
Source: VDMA 66412-1 : 2009-10
