Routing flexibility and production scheduling in a flexible manufacturing system

A multiproduct, multiperiod, multistage network model is presented for the planning of order release and production scheduling in a flexible manufacturing system environment under the existence of alternate routings. It is assumed that premanufacturing decisions such as machine grouping and tool loading have been made, so that setup costs and setup times are negligible and can be included in the processing times. The decision process addressed by the model is the disaggregation of weekly production requirements to daily production requirements, the determination of production batch sizes for each operation of each part type, and the daily assignment of each batch to machine groups given the flexibility of alternate routings. The model also provides the interface and linkage between an MRP component planning system and the shop scheduling system. The model is solved using a price-directive decomposition technique with column generation. Experimentation is performed with the model for varying problem sizes to determine the impact of shop flexibility on total cost, inventory levels, existence of bottlenecks, shop utilization, and the number of setups and split lot production. The results indicate important cost-benefit trade-off implications for system design and acquisition. For example, if in fact setup costs and times are nonnegligible, then it is shown that increasing the routing flexibility of a system without a parallel decrease in setup costs and times is unlikely to reap significant benefits.