The availability factor (also called availability) is a measure for losses due to the total of unplanned machine downtimes. According to eq. 1, it is defined as follows:
Eq. 1: Availability factor = Operating time / Oberating time + Downtime
The availability factor is reduced due to unplanned machine or equipment downtime as a result of the following exemplary events:
The availability factor is used to calculate the Overall Equipment Effectiveness (OEE).
For foundries, a agreement has to be made at what time an unplanned downtime is present. For keeping the time registration efforts under control, most foundries consider a registration limit of 1 minute of downtime to be a practical approach. All downtimes of less than one minute are included in the performance factor.
Whether setting reduces the OEE is a question of company-sepcific definition. If setting activities reduce the OEE, there is a motivation to reduce setting times through SMED (Single Minute Exchange of Die). On the other hand, this also results in an OEE increase through fewer modifications and higher batch sizes. However, this is contrary to the lean production principle. If, as agreed, setting activities do not reduce the OEE, there is the danger that disruptions are declared as setting activities which in fact they are not. The best way to handle setting times is to use standard setting time values. Planned setting times do not reduce the OEE, setting timeouts, however, do. For this purpose, standard setting time values have to be present, if necessary different values for different setting variants. The effort under these conditions might be very high.
Compared to the other OEE factors - use and quality factor - the availability factor is the easiest to determine. For this reason, OEE initiatives in foundries often begin with the availability factor determination.
Modern software with process data and time registration makes it possible to capture and visualize the availability factor.