Robust Storage Assignment in Unit-Load Warehouses

Published version made available in SMU repository with permission of INFORMS, 2014, February 28</p

Class-based storage location assignment : an overview of the literature

Storage, per se, is not only an important process in a warehouse, also it has the greatest influence on the most expensive one, i.e., order picking. This study aims to give a literature overview on class-based storage location assignment (CBSLAP). In this paper, we discuss storage policies and present a classification of storage location assignment problem. Next, different configuration of classes are presented. We identify the research gaps in the literature and conclude with promising future research directions

Warehouse design and product assignment and allocation: A mathematical programming model

Warehouses can be considered one of the most important nodes in supply chains. The dynamic nature of today's markets compels organizations to an incessant reassessment in an effort to respond to continuous challenges. Therefore warehouses must be continually re-evaluated to ensure that they are consistent with both market's demands and management's strategies. In this paper we discuss a mathematical programming model aiming to support product assignment and allocation to the functional areas as well as the size of each area. In particular a large mixed-integer programming model (MILP) is presented to capture the tradeoffs among the different warehouse costs in order to achieve global optimal design satisfying throughput requirements

Un modelo de optimización analítica para el diseño de centros de distribución baja políticas de alamacenamiento basadas en clases

The aim of this paper study the impact of class-based storage policy based on the optimal configuration of U-flow single command warehouses using a on an ABC product classification. For that purpose, the authors propose a non linear optimization model to minimize the expected travel distance of the warehouse and use analytical methods to solve it. The most important contribution is to provide a mathematical proof that regardless of the storage policy (It does not matter the specifics of the turnover pattern of the products), the optimal warehouse has a width that is the double of its length, and the pick and deposit point should be located in the middle of the width of the warehouse. In addition, authors perform a sensitivity analysis that indicates that the optimal solution is robust, meaning that a certain deviation from the optimum layout does not impose a significant penalty on the expected travel distance of the warehouse.Este artículo estudia el impacto de las políticas de alamacenamiento basadas en clases en el diseño de centros de distribución . Se asume una operación con una sola entrada y salida para los montacargas, los montacargas pueden transportar una unidad de carga al tiempo, y la política de almacenamiento es basada en la clasificación ABC de los productos. Se presenta un modelo de optimización no lineal para minimizar el valor esperado de la distancia por viaje del montacargas — un estimativo del costo de manejo de materiales — y se resuelve utilizando métodos analíticos. La contribución mas revelevante de este artículo es una demonstración matemática de que no independiente de la curva de distribución de la rotación de inventario de los productos, el diseño óptimo del centro de distribución es el mismo. Finalmente, el análisis de sensibilidad muestra que pequeñas desviaciones del desiño óptimo no afecta significativamente el costo de manejo de materiales

Maximizing space utilization in unit-load warehouses.

In a unit-load warehouse, products are stored and retrieved in pallet quantities. Examples include retail distribution centers (DC), third-party DCs, and transshipment hubs in freight transportation. Expenses related to space are a significant component of the operational cost of unit-load warehouses; therefore, maximizing space utilization is important. Moreover, the continuing revolution of retail e-commerce is changing the role and design of modern distribution centers (Boysen et al., 2018). An important trend with serious implications for design is the desire of many distributors to locate DCs in or near metropolitan areas in order to support same-day service or better (Thuermer, 2018). Land in these areas is very expensive, so there is a need to make the best use of existing space. The ability to store more products in the same space increases inventory availability and therefore service, and the ability to store the same inventory in a smaller footprint reduces costs. In this dissertation, we propose two strategies to improve space utilization in unit-load warehouses. We aim to minimize what we called loss of vertical space within slots (LVS)—the mismatch between the height of the pallet and the height of the slot where it is stored. LVS is a significant problem because it is standard practice to design storage racks in unit-load warehouses with all slots of equal height (maximum pallet height) such that every pallet can fit in every slot; however, pallet heights vary greatly. We propose the use of storage racks with multiple slot heights so that slot heights can better match the distribution of pallet heights. We analyzed historic (forecasted) inventory levels and the pallet heights to determine a robust design that guarantees a desired storage service level. Our method addresses the new warehouse design decisions that arise when having multiple slot heights: How to arrange the different slot heights in the rack-bays? How to organize the layout? How to avoid storage shortages? How do different slot heights affect travel times? We found that using multiple slot heights in unit-load warehouses has significant benefits in terms of footprint, expected travel time, and racking cost. For a typical warehouse, we expect space savings of 25–35 percent, depending on the number of slot types, and savings of 15–25 percent in annual operating cost. Although using multiple slot heights significantly decreases the loss of vertical space within slots, it does not completely eliminate it, and in warehouses where inventory levels are highly variable or product mixes change rapidly, this wasted space can still be significant. Examples of this situation in practice include warehouses with correlated order profiles, demands with seasonal peaks, new product launches, and distribution network consolidations. For such business environments, we propose pallet racks with dynamic heights as a way to maximize space utilization. Contrary to traditional pallet racks, the uprights and beams of pallet racks with dynamic heights are equipped with a mechanism to adjust slot heights easily. We found that pallet racks with dynamic heights have expected space savings of 16–30 percent when compared to traditional pallet racks

Advanced Storage and Retrieval Policies in Automated Warehouses

Warehouses are key components in supply chain. They facilitate the product flow from production to distribution. The performance of supply chains relies on the performance of warehouses and distribution centers. Being able to realize short order delivery lead times, in retail and ecommerce particularly, is important for warehouses. Efficient and responsive storage and retrieval operations can help in realizing a short order delivery lead time. Additionally, space scarcity has brought some companies to use high-density storage systems that increase space usage in the warehouse. In such storage systems, most of the available space is used for storing products, as little space is needed for transporting loads. However, the throughput capacity of high-density storage systems is typically low. New robotic and automated technologies help warehouses to increase their throughput and responsiveness. Warehouses adapting such technologies require customized storage and retrieval policies fit for automated operations. This thesis studies storage and retrieval policies in warehouses using several common and emerging automated technologies

Progress in Material Handling Research: 2012

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Operational-level Optimization of Inbound Intralogistics

This study is concerned with optimizing inbound operations at distribution centers (DCs), warehouses, and cross-docks with staging areas. The objective of the problem is to minimize the makespan required to move all unit loads from the trailers to the flow racks, and from the flow racks to their respective storage locations. It is assumed that a set of inbound trailers with known composition have been assigned and sequenced to inbound dock doors. The following three inbound logistics decisions are simultaneously considered: i) unloaders’ assignment and scheduling, ii) loads-to-flow rack assignment, and iii) assignment and haulers’ scheduling. In this study we describe the relationship between the problem of minimizing makespan and an unloader-hauler balancing problem. Three rule-based heuristics are proposed and evaluated in an instance of the problem

Progress in Material Handling Research: 2010

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