A Hybrid Metaheuristic Algorithm for Robust Two-stage Flexible Flow Shop scheduling with Dedicated Assembly Lines under Uncertainty

In this paper, the problem of scheduling and sequencing of multi-objective two-stage flexible flow shop with dedicated assembly lines, which produce various products during multiple planning periods, is proposed. The objectives of the proposed model are minimizing maximum completion time of products and total average weighted tardiness of production products. The first stage of the proposed flexible flow shop involves of several different parallel machines in site I and one machine in site II, and the second stage involves of two specific dedicated assembly lines. Each product has a specific bill of materials as well as has its own specific configuration which leading to difference processing times to assemble. Products composed of only single-process components are assigned to the first assembly line and products composed of at least a two-process component are assigned to the second assembly line. Components are placed on the associated dedicated assembly line in the second phase after completion of production process on the assigned machines in the first phase and final products will be produced by assembling the components. Uncertainty of demand of final products is handled via robust optimization technique based on the concept of uncertainty budget. The main contribution of this paper is development of a new mathematical model in flexible flow shop scheduling problem with dedicated assembly lines under uncertainty and presentation of a novel hybrid meta-heuristic for solving the proposed model. Due to the NP-hard nature of the proposed multi-objective problem, a hybrid evolutionary metaheuristic based on the strange Pareto evolutionary algorithm II is developed that incorporates a customized adaptive large neighborhood search as its local search heuristic. Extensive computational results illustrate the efficiency of the proposed model and solution algorithm in dealing with robust multi-objective flexible flow shop problem.