Enhancing the order picking process through simulation and optimization

Order picking is the most labour, time-consuming and cost-intensive process in warehousing. Besides its very own policies and practices, it is also affected both upstream from space allocation decisions and downstream by order reception and organization. As a result, the problems connected to planning and carrying out order picking operations can be dealt with by adopting a holistic-based approach offered by a proper decision support system. We propose a simulation-based optimization framework that benefits from mathematical programming models for the storage location assignment problem (SLAP) and the order picking problem, modelled as a variant of the Traveling Salesman Problem, i.e., the Picker Routing Problem (PRP). Then, simulation is used to mimic the overall order picking process occurring in a real distribution center. Preliminary numerical experiments are presented for different storage configurations and order picking strategies. Useful managerial insight follows scenario analysis in a rack-based warehouse featuring man-abroad vehicles that travel horizontally across the aisles according to an S-shape routing policy.