Integrating facility layout design and aisle structure in manufacturing systems: Formulation and exact solution

In manufacturing systems, aisles are paths which are used for the movement of workers, transportation devices, and materials. The aisle structure contributes to layout efficiency by reducing material handling costs, mean flow time and the amount of space needed, and providing smooth transportation. Therefore, to achieve a good layout, it is essential to determine the position of facilities such as machines and workstations, but also the corresponding aisle structure. In this article, we analyze the requirements for the design of an efficient aisle structure and propose a formulation of the corresponding layout problem as a mixed-integer linear programming model. This formulation allows the layout of unequal-area facilities and the aisle structure to be simultaneously optimized. In optimizing the aisle structure, issues such as optimizing the number, position, and width of the aisles, the position of the entrance and exit doors, and how to connect them to the aisles are studied. By optimizing the number and width of the aisles, the proposed approach contributes towards optimizing transportation traffic. A branch-and-cut algorithm, improved by adding optimality cuts and efficient branching and node strategies, is used to solve the problem. Finally, a set of computational experiments is performed to show the effectiveness of the proposed approach.