A flexible approach to part type selection in flexible flow systems using part mix ratios

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Abstract
The short-term production planning function for setting up a flexible manufacturing system (FMS) prior to production should be developed so as to interact well with the operation of the system over time. During FMS operation, planning for system set-up has to be performed somewhat periodically, for example, when the part mix is changed, or when the production requirements are finished for some part types, or when a machine breaks down. Since all cutting tools required for all part types that need to be machined cannot usually fit in the machines' limited capacity tool magazines, decisions need to be made concerning which part types will be produced next. This paper suggests a more flexible approach than is typical for short-term production planning. The differences between the proposed flexible approach and previous approaches taken in the literature and in industry to solve these problems are provided. A description of when either a batching or a flexible approach is appropriate is provided. An existing mathematical programming procedure that determines balanced (or unbalanced) part mix ratios for part types to balance machine workloads is adapted to solve another planning problem of selecting part types to be machined together over the upcoming time period. A simulation model is developed to demonstrate the implementation of both the suggested flexible approach and batching on a realistic flexible flow system (FFS) having pooled machines of unequal sizes. The research results indicate that: (1) the flexible approach usually leads to better system utilization and makespan than batching; (2) using the flexible approach enables the system to be utilized more constantly; and (3) the flexible approach requires fewer fixtures dedicated to particular part types than batching to complete the production requirements of all part times. Computational results are presented to demonstrate the performance of the part type selection approaches. Further research needs are also discussed.