A bi-objective mathematical model for product allocation in block stacking warehouses

Put-away and picking operations in warehouses play a critical role in determining operating costs and customer response time. While the place where products are put away has an important effect on picking efficiency due to accessibility, it also affects space usage, which is critical for space availability and space costs. Hence, this study focuses on put-away operations in pallet-in pallet-out block stacking warehouses. We develop a unique bi-objective mathematical model and a constructive heuristic algorithm to allocate products to storage lanes while considering two objectives simultaneously: minimizing total travel distance and maximizing average storage usage. We test our model and heuristic through a real company case study and randomly generated large-sized problem instances. We show that the model and heuristic offer better storage usage with reduced travel distance than the company's approach when the two objectives have equal weight. We also present a set of nondominated solutions for each problem instance. We present that the heuristic seems beneficial for the warehouse industry due to its short run time and effective solutions.