Work scheduling in FMS under tool availability constraints†

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Abstract
Various of the planning problems in FMS are introduced and the impact of tooling considerations observed. The effect of tool variety, product variety and product similarity on the frequency of two types of tool change, due to product variety and due to tool wear, are identified. It is shown that when variety is great tooling availability constrains scheduling decisions. The problem area is illustrated with reference to an example FMS, for which it is shown that tool capacity constrains scheduling decisions. The possibility of developing some part launch sequence which would minimize the need for tool changes is considered but found ineffective. Dynamically selecting jobs from queues so as to minimize tool change is also found ineffective. A linear programming mode, due to Menon and O'Gradey (1984), is described, but found to require further evaluation. A tooling post-processor for a simulation model is presented which computes the number of tool changes in any work schedule. For the FMS considered it is found that the number of tool changes due to product variety is small compared to those due to tool wear. It is concluded that the assumptions underlying some of the FMS planning problems must be reconsidered in view of this result.

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