The impact of lot sizing and sequencing on manufacturing performance in a two-stage hybrid flow shop

This paper deals with the problem of production scheduling in a two-stage hybrid flow shop, which consists of one machine in the first stage, and multiple process lines in the second stage. In the first stage, materials are batch-processed, which are then fed into one of several process lines in the second stage, depending on the final product specifications. First, the authors formulated the total flow time or makespan, the capacity utilization and the maximum work-in-process level as measures of manufacturing performance. They analysed, through a series of numerical experiments, how these performance measures are affected by lot sizing, sequencing rules and the scheduling scenario. The following points were clarified. (1) The ratio rule yields the best performance with regard to the makespan, but the LPT rule yields the best performance with regard to the maximum work-in-process level. (2) The optimum lot size is also affected by such operation conditions as the unit processing time, the setup time, and the ratio of unit processing times in the two stages. (3) The starting point for making a schedule should be set in the bottleneck stage with regard to the makespan.