Group Scheduling Problems in Flexible Flow Shops

Flexible flow shops are becoming increasingly common in industry practice because of higher workloads imposed by jobs on one or more stages, thus requiring two or more units of the same machine type. We present a methodology for solving this important problem, namely group scheduling, within the context of cellular manufacturing systems in order to minimize the total completion time of all groups of jobs considered in the planning horizon. Two different setup options, namely single setup and multiple-setups, are investigated for jobs within the same group. A combined heuristic solution algorithm, comprised of singleand multiple-pass heuristics, is used for solving the problem. An example problem, consisting of three different problem instances of the same structure, is used to not only demonstrate the applicability of the solution algorithm, but also to identify the setup to average job run time ratios that should simultaneously prevail across all stages represented by two or more identical units in order to select multiple-setups over single setup or vice versa.