Combining matheuristics and MILP to solve the accessibility windows assembly line balancing problem level 2 (AWALBP-L2)

We propose an approach combining a matheuristic and a MILP model to solve the variant Level 2 of the Accessibility Windows Assembly Line Balancing Problem (AWALBP-L2). This is a novel problem that arises in those real-world assembly lines where, in contrast to the most common ones, the length of the workpieces is larger than the widths of the workstations. This means that, at any time, a workstation cannot access an entire workpiece, but only a restricted portion of a workpiece or two consecutive workpieces. As a result, a workstation can only perform, at any time, the subset of tasks that fall inside its accessible area. The problem is to solve the task assignment and the movement scheme subproblems, while minimizing the cycle time. The proposed solving approach consists of (i) a matheuristic to generate good feasible solutions and compute bounds and (ii) a MILP model that makes use of the obtained bounds. A computational study is carried out to compare the performance of the proposed approach with the existing literature.