Abstract:

Being a common issue faced by nowadays production managers, the problem of minimizing the makespan of batch production schedules of items by using the lot streaming strategy in hybrid flow shops is insufficiently studied by operations researchers. To address to the limitations found in the literature concerning the subject, this paper formulates two comprehensive mathematical models for the problem, a linear programming model and an enumeration model. These models accounts of the following application conditions for lot streaming strategy in a hybrid flow shop: a prescribed cycle time limit must be met by the batch production process of item; no-idling of batch operations is to be ensured; transportation times of streamed lots between processing stages and alternative processing schemes for lots by parallel machines in each stage are considered; setup times for stage operations and alterative schemes for scheduling setup work are assumed; a fixed number of streamed lots and an equal size of lots must be used. The implementation of the models with convenient spreadsheet optimization tools is also presented. An optimization add-in for Microsoft Office Excel was used for solving the linear programming model, and a VBA procedure was coded for the enumeration model. A numerical example for the utilization of the models is finally given, in order to discuss the quality of scheduling solutions under different models’ settings, and also to compare these solutions using equal-size lots with other provided scheduling solutions using optimally sized, different in size lots.