Minimizing Total Tardiness in a Hybrid Flexible Flowshop with Sequence Dependent Setup Times

In this paper, we propose different local search algorithms to solve a realistic variant of the flowshop problem. The variant considered here is a hybrid flexible flowshop problem with sequence-dependent setup times, and with the objective of minimizing the total tardiness. In this variant of flowshop, stage skipping might occur, i.e., not all stages must be visited by all jobs. This scheduling problem is frequently used in batch production, helping to reduce the gap between research and operational use. While there is some research on minimizing the makespan, to our knowledge no work has been reported on minimizing the total tardiness for this problem. The proposed approaches present different neighborhood searches. Numerical experiments compare the performance of the different algorithms on new benchmarks generated for this problem. Keywords—hybrid flexible flowshop; sequence dependent setup times; total tardiness; local search; scheduling.