Sequencing Heuristics for Flexible Flow Shop Scheduling Problems with Unrelated Parallel Machines and Setup Times

This paper presents an investigation of scheduling procedures to seek the minimum of a positively weighted convex sum of makespan and the number of tardy jobs in a static flexible flow shop scheduling environment. The flexible flow shop problem is a scheduling of jobs in a flow shop environment consisting of series of production stages, some of which may have only one machine, but at least one stage must have multiple machines. In addition, sequence and machine dependent setup times are considered. No preemption of jobs is allowed. Some dispatching rules and flow shop makespan heuristics are adapted for sequencing in the flexible flow shop problem. The improvement heuristic algorithms such as shift and pairwise interchange algorithms have been proposed. Upon these heuristics, the first stage sequence is generated by using them. The first stage sequence will now be used, in conjunction with either permutation or FIFO rules, to construct a schedule for the problem. The solution is then set equal to the best function value obtained by both rules. The performance of the heuristics is compared relative to the optimal solution on a set of small-scale test problems.