A dock-door assignment problem for the Korean mail distribution center

This paper addresses operational problems of the cross-docking system in a mail distribution center. The center has two types of doors, receiving doors and shipping doors. The assignment of destinations to shipping doors, clustering of destinations to form groups, and determination of the number of groups are major operational problems directly related with the efficiency of the center. To solve the problems, a non-linear mathematical model is developed with the objective of minimizing the travel distance of the pallets in the center. For the model, two solution methods, three-phase heuristic procedure and genetic algorithm, are developed. A lower bound is also found to evaluate the validity of the solution methods. A case with the real world data is solved and a substantial improvement is obtained by the model compared with the current operating system.