Cross-docking: State of the art

Cross-docking is a logistics strategy in which freight is unloaded from inbound vehicles and (almost) directly loaded into outbound vehicles, with little or no storage in between. This paper presents an overview of the cross-docking concept. Guidelines for the successful use and implementation of cross-docking are discussed and several characteristics are described that can be used to distinguish between different cross-dock types. In addition, this paper presents an extensive review of the existing literature about cross-docking. The discussed papers are classified based on the problem type that is tackled (ranging from more strategic or tactical to more operational problems). Based on this review, several opportunities to improve and extend the current research are indicated.     

A comparative study of formulations for a cross-dock door assignment problem

A cross docking facility is a type of warehouse in supply chain management that allows orders to be prepared with or without going through the phase of storing products in the warehouse and subsequently selecting them for delivery. The goods are unloaded from incoming trucks called origins on inbound doors of a cross-docking facility platform and, using a handling device inside the platform such as a forklift, immediately transferred to outbound doors to be loaded into outgoing trucks named destinations or delivery trucks for distribution to customers. Contrary to a traditional warehouse, goods are unloaded and loaded without placing them in temporary storage inside the cross-docking facility. The goal of the cross-docking assignment problem (CDAP) is to assign origins to inbound doors and destinations to outbound doors so that the total cost inside the cross-dock platform is minimized. To the best of our knowledge, there are only three mixed integer programming (MIP) formulations of the CDAP in the literature. We propose eight new MIP models and demonstrate the mathematical equivalence of all 11 models, together with rigorously proving some of their properties. In order to detect which of these 11 models is best, we conduct an extensive comparative analysis on benchmark instances from the literature, which discloses that the best model is one proposed in this paper for the first time.     

越库配送下考虑时空距离的库门分配与车辆调度优化

针对越库配送下考虑时空距离的库门分配与车辆路径问题,建立以车辆派遣成本、运输成本、时间惩罚成本、越库内部操作成本总和最小化为目标的库门分配与车辆路径优化模型。根据问题的特征设计改进的自适应遗传算法,并根据时空距离生成初始解。通过对不同规模的算例进行对比和分析,验证了模型的正确性和算法的有效性,结果表明,所得出的库门分配和车辆调度优化方案可以有效降低越库配送中心的运营成本。研究成果拓展和丰富了越库配送下的车辆路径问题研究,能为物流企业优化配送方案提供理论依据。     

A joint economic lot size model for raw material ordering,manufacturing setup,and finished goods delivering

In this research we consider a single-manufacturer single-buyer supply chain problem where the manufacturer orders raw materials from its supplier, then using its manufacturing processes converts the raw materials to finished goods, and finally delivers the finished goods to its customer. The manufacturer produces the product in batches at a finite rate and periodically delivers the finished goods at a fixed lot size to its customer, who has a constant demand rate. An integrated inventory control model, making joint economic lot sizes of manufacturer's raw material ordering, production batch, and buyer's ordering, is developed to minimize the mean total cost per unit time of the raw materials ordering and holding, manufacturer's setup and finished goods holding, the buyer's ordering, and inventory holding. Numerical examples are also setup to illustrate that jointly considering the inventory costs above results in less mean total cost than that of considering them separately.     

A solution framework for the multi-mode resource-constrained cross-dock scheduling problem

In this paper we propose a framework for shift-level container scheduling and resource allocation decisions at a cross-dock facility. The Multi-Mode Resource-Constrained Cross-Dock Scheduling Problem (MRCDSP) approach minimizes material flow and schedules inbound and outbound containers to dock-doors such that the total processing time is minimized subject to the resource constraints at the cross-dock. While container scheduling and resource allocation problems at cross-dock facilities have been studied previously in isolation, our work is the first to consider a complete view of cross-dock operations providing optimal container to dock-door allocation, and a makespan minimizing schedule of containers to the cross-dock. We present a comprehensive framework that includes identification of container clusters to reduce the problem size, a container-to-dock-door assignment algorithm, and a container clusters scheduling model that is solvable for practically sized problems. In a comparative numeric study based on data simulating a cross-dock facility, our approach is shown to outperform current practice, reducing the average time required for processing a set of containers by 37% and reducing the weighted-distance material traveled within the cross-dock by 45%.     

The benefits of a cross-docking delivery strategy: a supply chain collaboration approach

In this study, two models are developed to co-ordinate both production and distribution in order to reduce the relevant costs in a supply chain. According to the functions of the distribution centre, there is a distinction between an inventory co-ordination point and an inventory storage point. The former is a cross-docking strategy, and the latter is a traditional warehousing strategy. The manufacturer has distinct production processes when co-operating with the distribution centre. Case study analysis is used to illustrate the models developed, in which the following conclusions can be obtained: the cross-docking distribution strategy will result in tremendous savings in the total system cost for the supply chain. This study makes two important contributions to the production, and logistics literature. First, the range of applications was extended by studying a new combinatorial problem that incorporates cross-docking in a supply chain environment. Second, computational performance with cross docking was evaluated. The benefit delivery policy for a distribution centre was found by means of integrating manufacturer production planning and a distribution centre delivery policy.     

Modeling the manager's match-or-wait dilemma in a make-to-forecast production situation

The make-to-forecast manufacturing environment is characterized by the manufacture of individual, expensive-to-store units which come in alternative configurations or models. Since the production lead times are longer than customers are willing to wait, production is started in anticipation of orders for particular models and then modified while in production, if economically desirable, to match the actual customer orders. Ideally, no finished goods inventory occurs in this process. Occasionally, however, such unsold finished items (called “orphans” here) are generated. Since their holding cost is substantial, especially if they are physically large and hard to store, the orphans become a serious managerial problem. The dilemma management faces with an orphan is: should the orphan be modified (to the specifications of a new order) to dispose of it now, perhaps even at a loss, or should it be held another period (thereby incurring the substantial holding cost) for a possibly better matching order with a more tolerable modification cost?     

基于消费者搜寻成本的商圈形成机理研究

基于Nelson搜寻成本节约相关理论,通过引入购物成本、品味搜寻成本Ι、品味搜寻成本ΙΙ以及区位搜寻成本等概念,在深入阐释消费者搜寻与购物行为基础上,构建了消费者商圈搜寻期望经济学模型。研究结果表明:第一,商圈商品所能提供的满意度随消费者对商品要求提高或商圈内搜寻新店成本减小而增加;第二,孤立企业商品所能提供的满意度随消费者对商品要求提高、商圈内企业数量增加或商圈内搜寻新店成本减小而增加;第三,商品的区位搜寻成本,以及商圈到孤立企业间距离的影响则由商圈与孤立企业各自所能提供商品的满意度比较情况而决定。同时,结合徐家汇商圈形成案例的分析对以上结论进行了进一步探讨与分析。     

零售物流中心运作优化的一种T型补货策略

现代零售物流中心一般都包含数十万个大大小小的货位,每日需处理几万到数十万货位品类（SKU）的物流运作。如何合理存储货品并将货品从存储位补充至拣货位,即补货,是仓储管理中常见的瓶颈流程,直接决定了零售物流中心的作业效率。该研究基于虚拟商务理论提出了一种新的T型补货策略,即以拣货位为基点,呈T字形搜索寻址来上架存储货品,并按照先入先出和就近原则将货品补充至拣货位。与常规补货策略相比,T型补货策略不只是考虑单一货品的补充距离,更注重物流中心存储的整体合理性。最后以中国某百强连锁零售企业在上海的物流中心为例,抽取了采用T型补货策略前后的10000条数据并进行分析,结果显示T型补货策略极大地提升了物流中心的补货效率。     

蓄冷式多温集配路径优化模型

现实中,由于配送中心选址对占地面积、土地成本等要求较高,加之物流企业资金有限或交通拥堵等限制,配送中心的设置通常会远离市中心。为了减少集货与配送车辆往返配送中心的次数以及车辆行驶距离,本文以总成本最小化,包括车辆派遣成本、行驶成本、碳排放成本、违背时间窗的惩罚成本、保温柜/箱成本、非整箱货物的配送成本,构建了1个配送中心由大型车辆为m个供应商采用蓄冷柜/蓄冷箱集货,由1个虚拟接驳点(中型车辆)结合小型车辆为n个零售门店采用蓄冷箱多温共配的路径优化模型,并设计了基于蚁群算法的混合更新信息素策略。以20个零售门店与6个海鲜供应商的三种品温海鲜品为仿真算例,验证了模型的有效性。实例分析发现：引入虚拟接驳点的配送线路数低于单纯的配送线路数;时间窗限制越宽松,引入虚拟接驳点的优越性越突出;具有虚拟接驳点的多温集配总成本低于自配送中心的集配总成本;具有虚拟接驳点的蓄冷式多温集配尤其利于低碳环保的冷链系统构建。     

Customer‐Base Concentration and Inventory Efficiencies: Evidence from the Manufacturing Sector

What is the link between customer‐base concentration and inventory efficiencies in the manufacturing sector? Using hand‐collected data from 10‐K Filings, we find that manufacturers with more concentrated customer bases hold fewer inventories for less time and are less likely to end up with excess inventories, as indicated by the lower likelihood and magnitude of inventory write‐downs and reversals. Using disaggregated inventory disclosures, we find that inventory efficiencies primarily flow through the finished goods inventory account, while raw material efficiencies are offset by higher work‐in‐process holdings and longer work‐in‐process cycles. In additional analysis, we document a valuation premium for more concentrated manufacturers after controlling for other firm characteristics, including default risk and cost of capital estimates. We conclude that investors trade off the costs and benefits of relationships with a limited number of major customers and, on balance, consider customer‐base concentration as a net positive for firm valuation. Overall, our study adds to interdisciplinary research in accounting and operations management by shedding new light on the relevance of major customer disclosures for fundamental analysis and valuation in the manufacturing sector.     

On‐Shelf Availability,Retail Performance,and External Audits: A Field Experiment

A potential answer to retailer's shelf out‐of‐stocks (OOS), where the item is in the store but customers cannot find it, is to employ third‐party service providers to execute audits and corrections. However, given the nontrivial cost of executing external audits, it is still necessary to assess whether external audits are capable of reducing shelf‐OOS, whether they can be performed in an economical way, and whether the benefits from the audits translate into higher sales. In an effort to address these questions, we partnered with a product manufacturer and a retail service provider and conducted a field experiment in a national retailer's store set. We used transactional data to detect abnormal operations and respond to possible shelf‐OOS by sending auditors to correct empty shelves and incorrect inventory records. At the conclusion of the experiment, we found that Stock Keeping Units in the treatment group were less likely to have shelf‐OOS and inventory record inaccuracies, and that our intervention had a positive effect on sales. Furthermore, we found that the external audit initiative is economically viable since these improvements required low auditing efforts after a transitional period, and in steady state the cost of running the program is a small fraction of the benefits it generates. We discuss the limitations of our study and the implications of our findings for researchers and practitioners.     

部分短缺量拖后下基于顾客敏感度的补货策略适用范围研究

顾客对缺货数量和等待时间的敏感度影响着部分短缺量拖后率。基于此,根据顾客对缺货数量和等待时间的敏感度以及成本结构,对部分短缺量拖后下不同补货策略的适用范围进行了研究,得出以下结论:(s,S)连续性检查策略适用于单位缺货和丢单成本较高的库存系统;(t,S)周期性检查策略和(t,s,S)混合策略适用于单位缺货和丢单成本较低的库存系统;在单位缺货和丢单成本较低的库存系统中,当顾客对缺货数量较敏感时,(t,s,S)混合策略的运作成本更低,否则(t,S)周期性检查策略更适用,而顾客对等待时间的敏感度对补货策略适用范围的影响不明显。     

The effects of learning and forgetting on the optimal lot size quantity of intermittent production runs

This paper studies the effects of learning and forgetting on the production lot size problem with infinite and finite planning horizons. It is assumed that the determination of the economic manufactured quantity (EMQ) in the succeeding production run is dependent on: (1) the maximum inventory accumulated prior to interruption; (2) the length of the interruption period which incurs total forgetting; and (3) the level of experience in equivalent units remembered at the start-up of the next production run. The optimum operating inventory doctrines is obtained by trading off procurement cost per unit time and the inventory carrying cost per unit time, so that their sum will be a minimum. A numerical example is presented to demonstrate the application of learning and forgetting to the determination of the EMQ.     

The Impact of the Online Channel on Retailers' Performances: An Empirical Evaluation

The use of the Internet as an additional sales channel offers traditional retailers opportunities to reach expanded markets while improving the efficiency of their operations. Although the potential benefits of the online channel are clear, there are significant variations in the scope and depth of online channel use among retailers. Drawing from data on more than 100 publicly traded companies, this study examines the impact of online‐channel use on retailers’ performance. The results suggest that the online channel provides significant improvements in sales, cost, inventory, and return on investments. In addition, we find that the timing of online‐channel adoption does not play a significant role in performance improvement, but having a local store presence does.     

The resource constrained single-item inventory problem with demand-dependent unit cost

In this paper, we present an economic order quantity (EOQ) with both demand-dependent unit cost and restrictions. An analytical solution of the EQO is derived using a recent and simple method, which isthe geometric programming approach. The EOQ inventory model with demand-dependent unit cost without any restriction and the classical EOQ inventory model are obtained.     

Combined Pricing and Portfolio Option Procurement

In this paper, we study a single‐product periodic‐review inventory system that faces random and price‐dependent demand. The firm can purchase the product either from option contracts or from the spot market. Different option contracts are offered by a set of suppliers with a two‐part fee structure: a unit reservation cost and a unit exercising cost. The spot market price is random and its realization may affect the subsequent option contract prices. The firm decides the reservation quantity from each supplier and the product selling price at the beginning of each period and the number of options to exercise (inventory replenishment) at the end of the period to maximize the total expected profit over its planning horizon. We show that the optimal inventory replenishment policy is order‐up‐to type with a sequence of decreasing thresholds. We also investigate the optimal option‐reservation policy and the optimal pricing strategy. The optimal reservation quantities and selling price are shown to be both decreasing in the starting inventory level when demand function is additive. Building upon the analytical results, we conduct a numerical study to unveil additional managerial insights. Among other things, we quantify the values of the option contracts and dynamic pricing to the firm and show that they are more significant when the market demand becomes more volatile.     

An echelon inventory-based single-stage cost function for a two-station tandem system

We propose an alternative cost-accounting function for inventory control problems on a make-to-stock setting. Our proposal is based on observing that the traditional holding and backlog parameters introduce some odd short term distortions on the inventory state space. Our single-stage cost function accounts for echelon inventories and possesses a pair of cost parameters for each echelon inventory variable, depending on whether it is positive or negative. With the modified cost-accounting function, we study a twostation tandem system producing a single product, and investigate how it compares with the performances obtained with the usual single-stage cost function. The results available so far show that the optimal policies approach a multi-echelon base stock structure for each machine. Also, the service levels achieved are better under the modified function without increasing the levels of finished goods inventory.     

含服务水平约束的可控提前期供应链Staekelberg模型与协调机制研究

为了有效地缩短订货提前期与降低库存成本,首先从Stackelberg主从对策角度建立了含服务水平约束的可控提前期供应链库存优化模型,提出了该模型的求解算法;然后从集中决策角度建立了另一类含服务水平约束的可控提前期供应链库存优化模型,并提出该模型的求解算法。利用数值分析对两类模型的优化效果进行比较,结果表明:集中决策模式下的优化效果明显优于Stackelberg主从对策模式下的优化效果,但在缺乏合理的激励机制情形下,供应链各参与方未必有足够积极性接受集中决策模式。为此,提出一种库存费用分担机制来激励供应链各参与方接受集中决策模式。     

A Production–Inventory Model for a Push–Pull Manufacturing System with Capacity and Service Level Constraints

We study a hybrid push–pull production system with a two‐stage manufacturing process, which builds and stocks tested components for just‐in‐time configuration of the final product when a specific customer order is received. The first production stage (fabrication) is a push process where parts are replenished, tested, and assembled into components according to product‐level build plans. The component inventory is kept in stock ready for the final assembly of the end products. The second production stage (fulfillment) is a pull‐based assemble‐to‐order process where the final assembly process is initiated when a customer order is received and no finished goods inventory is kept for end products. One important planning issue is to find the right trade‐off between capacity utilization and inventory cost reduction that strives to meet the quarter‐end peak demand. We present a nonlinear optimization model to minimize the total inventory cost subject to the service level constraints and the production capacity constraints. This results in a convex program with linear constraints. An efficient algorithm using decomposition is developed for solving the nonlinear optimization problem. Numerical results are presented to show the performance improvements achieved by the optimized solutions along with managerial insights provided.