| Quarter Billion dollars could be saved annually by double stacking pallets. A forklift storing 100 double stacked pallets saves 2.5 working hours versus single pallets. More than one billion pallets and cases handled between Wal-Mart distribution centers according to BEA White Paper (2006) [1], assume only 500 million were stackable pallets. This translates to 12.5 million working hours. If a forklift driver earns ;Moreover, handling double stacked pallets takes up to 46 % of total time to pick and store. This is a significant element that was ignored in literature. All previous research focused only on travel time that is just part of the total time.;In this dissertation we model dual command operations to find optimal path with minimum travel time. Combination of both picking and storage activities is also known as dual command. Our environment is a manual warehouse where full pallets can be double stacked. Accordingly, three time-based models were developed as 123 steps to reach dual command model; order picking model, storage model and combined storage and order picking model. The mathematical models find the optimal sequence of storing and picking pallets that leads to the minimum travel time. Using those models allow double stacking pallets, therefore around half of material handling time, labor cost, and equipment cost will be saved compared to single stacked pallet operations. Two heuristics were also developed that gave sub optimal but quicker solutions that can also be used by the warehouse management and reduce the travel time significantly as well. |
