Dimitris Mourtzis et al. / Procedia CIRP 79 (2019) 574–579
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Fig. 1. Workflow of the proposed methodology.
12. Calculate average inventory 13. Calculate the inventory cost
It has to be pointed out a set of assumptions have been made to tackle the obstacles in the following categories: a) demand uncertainty, b) Constant Order Quantity, c) Constant Re-Order Point, d) Suppliers/Production Inconsistency and e) Economic Order Quantity model. The methodology consists of two basic parts with a total number of 23 steps; warehouse design (18 steps) and warehouse simulation (5 steps) as presented in Figure 1. 3.1 Warehouse Design The design of a well-structured warehouse system concerns a large number of interrelated decisions/ steps which have to be placed in a hierarchical framework. Input data are crucial for reaching a viable verdict on the proper operation. In our methodology, three input data are inserted: products, orders and demand profiles. Then, the proposed methodology is followed to define the warehouse design requirements. The steps of the proposed methodology are listed below (also presented Figure 1 in blue color): 1. Based on the real demand, the forecast for the next month is created 2. its deviation from the real demand is calculated 3. The mean and standard deviation for each product is calculated 4. Define the desired service level and based on that, the z value 5. Calculate safety inventory and the annual consumption 6. Calculate storage cost and parcel price 7. Calculate the deviation between forecasted and actual demand
14. Define product consumption and required warehouse size 15. Calculate final warehouse metrics (size, inventory costs, productivity) 16. Re-run for different values for service level, storage cost and production cycle 17. Define the optimal scenario, which minimizes inventory costs and warehouse size 18. Design the warehouse layout. 3.2 Warehouse simulation Warehouse simulation is a way of testing different scenarios in real life without any interruption in the production rate. As a result, it gives the opportunity to compare and select the best scenario which will cover warehouse demands. According to warehouse design data, the warehouse model is built. The warehouse model includes: a source for each product, a queue before and after each palletizing station, forklifts according to warehouse capacity which carry pallets to warehouse, the calculated warehouse area where products are stocked, forklifts according to warehouse capacity which carry pallets from warehouse area to each loading area/ exit and a queue to each loading area-exit. All the above are properly linked and programmed so as to simulate a virtual warehouse environment and operation, while the parameters of each testing scenario are defined. Then, the possible warehouse layouts are defined and run, while their performance is compared and the optimum solution is selected. The result is then verified, comparing the results from the simulation and the design methodology, and if valid, is applied in the warehouse. 3.3 Augmented Reality application for inventory management Together with the new layout that will be suggested, an application that will support inventory management and
8. Calculate Economic Order Quantity 9. Define the number of annual orders 10. Calculate time for inventory re-ordering 11. Define the size of order
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