Green scheduling of a two-machine flowshop:Trade-off between makespan and energy consumption

Sustainability considerations in manufacturing scheduling, which is traditionally influenced by service oriented performance metrics, have rarely been adopted in the literature. This paper aims to address this gap by incorporating energy consumption as an explicit criterion in shop floor scheduling. Leveraging the variable speed of machineing operations leading to different energy consumption levels, we explore the potential for energy saving in manufacturing. We analyse the trade-off between minimizing makes pan, a measure of service level and total energy consumption, an indicator for environmental sustainability of a two-machine sequence depend entpermutation flow shop. We develop a mixed integer linear multi-objective optimization model to find the Pare to frontier comprised of makes pan and total energy consumption. To cope with combinatorial complexity, we also develop a constructive heuristic for fast trade off analysis between makes pan and energy consumption. We define lower bounds for the two objectives under some non-restrictive conditions and compare the performance of the constructive heuristic with CPLEX through design of experiments. The lower bounds that we develop are valid under realistic assumptions since they are condition alon speed factors. The Pare to frontier includes solution sranging from expedited, energy intensive schedules to pro-longed, energy efficient schedules. It can serve as a visual aid for production and sales planners to consider energy consumption explicitly in making quick decisions while negotiating with customers on due dates. We provide managerialin sights by analysing the are as a long the Pare to frontier where energy saving can be justified at the expense of reduced service level and vice versa