A MILP optimization model for the dock-assignment in a multi-door cross-docking hub

Cross-docking is a logistic strategy for shipping goods from suppliers to customers without intermediate storage, using a hub to exchange freights from one truck to another. Goods are collected from several suppliers via inbound trucks, unloaded in the cross-dock hub, reconsolidated with other goods and loaded into outbound trucks heading toward the customers. This study focuses on optimising the handling activities required to unload, move, and reload the goods inside cross-dock terminals by developing and applying an original mixed-integer linear programming model. This model aims to determine the optimal solution for formulating the dock-assignment problem in a multi-door cross-docking system, where multiple trucks can simultaneously unload (inbound) and reload (outbound) palletised until-loads. The objective function minimises the travelling time spent by forklifts moving palletised until-loads from inbound to outbound docks. Furthermore, a twin hub nearby provides extra doors for cross-docking operations. The model identifies and controls the trade-off between truck-based and shuttle-based transferring activities among hubs. The proposed model is applied to a cross-docking hub made of two twin facilities owned by an Italian company specialised in the fast delivery of palletised unit-loads (called loads). A comparative what-if multi-scenario analysis demonstrates the effectiveness of the proposed model in reducing the time-to-shipping of loads.