Availability of CNC machines: multiple-input transfer-function modeling

Computer numerical control (CNC) machines are an integral part of FMSs (flexible manufacturing systems). Frequent breakdown of CNC machines can lead to an unacceptable level of downtimes in FMSs. The acquisition of CNC machines has been justified on economic grounds; however, some analyses do not consider the breakdown of CNC machines. The interrelationship between the downtimes, type of breakdown, and uptimes of CNC machines is explored. The data are analyzed using multiple-input transfer-function modeling. The authors´ approach is a prototype for the analysis of reliability data involving three interrelated sources of data. They show that: (i) uptime is not a leading indicator of downtime; (ii) downtimes and uptimes are not importantly related in the same period, and (iii) each CNC machine downtime has a forward effect on the uptime; however, influence is delayed from 1 to 7 downtime periods. The modeling provides management with useful information for assessing maintenance policies, making replacement policy decisions, and evaluating the availability and readiness of CNC machines. The models can provide decision makers with superior short-term forecasting and important maintenance information which could be used in the development of production plans and future machine requirements