Improving global spare parts distribution chain performance through part categorization: A case study

Spare parts inventory management is a complex problem and in most cases part categorization is needed to create a manageable number of control groups to focus management efforts more effectively. Usually multi-dimensional or multi-criteria classifications are used, and there are several examples of classification schemes available in the literature. The complexity increases even more when taking into consideration that a distribution chain consists of many parties. Thus, in addition to internal inventory control factors, external factors such as supplier performance, customer behavior and related demand patterns affect the controllability of the various parts.In the paper we try to expand existing classification schemes that cover only one part of the supply chain into a decision tool covering three sides of the chain: the company's distribution center with its internal processes, supplier with supply processes and customer with demand processes. The complexity that is created by the expanded view is reduced by considering two separate links: demand link and supply link. At first the links are analyzed separately considering the most relevant factors of each one and afterwards they are combined into a categorization matrix to classify the parts.The categorization scheme is tested in a large international company for improving its spare parts distribution chain performance. In the case company's demand link, part value and demand variability were used as the factors to create seven categories. In supply link, three categories are created by using availability risk of the material as the categorizing factor. The spare parts distribution chain performance is analyzed with service performance and stock-out cost key performance indicators before and after improvement actions. Finally, it is discussed how widely the insights from the case experience can be generalized towards developing a generic management tool for such a complex situation.     

Reducing the mean supply delay of spare parts using lateral transshipments policies

Lateral transshipment has been studied lately as a promising policy for increasing the performances of multi-echelon spare parts inventory system. By lateral transshipment spare parts can be moved from one location with excess inventory to another location, at the same echelon, in shortage, with the aim of reducing supply delays of spare parts. This paper will examine the relative effectiveness of two lateral shipments approaches in reducing the mean supply delay (MSD) of a non-repairable item, with respect to a classical policy of no lateral shipments. A simulation model of a two echelon supply network has been implemented and an experiment has been performed by varying different parameters of the supply network, such as the number of warehouses (locations at the lower echelon), the supply lead time from the central depot, the spare parts demand uncertainty, and the size variability of the warehouses. Results show appreciable reductions of MSD when lateral shipments are allowed with respect to the classical policy, in almost every network configuration.     

On how buyback and remanufacturing strategies affect the profitability of spare parts supply chains

The purpose of this paper is to provide a case-based framework to offer insights on the opportunity of recovering parts. We consider a two-stage spare parts supply chain, where independent repair shops are responsible for handling the repair process. There are two options to meet spare parts demand: repair shops may replace the part with a new one (ordered from the OEM) or they may use a part that they themselves repaired before. While repair shops achieve a larger profit by repairing parts, the OEM would prefer the use of new parts. However, he has no control over demand which might be obtained by offering buyback of broken parts. Furthermore, the OEM could recover these parts on a higher level, thus reducing production/procurement of new parts. The main contribution of this paper is the provision of a simple deterministic framework for answering the question whether a buyback option should be offered by the OEM to the repair shops, and which buyback price should be paid for each returned core. We further highlight the impact of remanufacturing performed at the OEM on the profitability of buyback.     

An analysis of the inventory behavior in a q-theoretic framework

This paper develops a generalized q-model in which a monopolist with perfect foresight holds inventories. This model permits an analysis of the dynamics of inventories in the presence of various types of deterministic demand and supply shocks. The results suggest that if only positive inventories are allowed, inventories are more successful in smoothing expected upward than downward variations in demand. If unfilled orders are permitted, then production smoothing accompanies any type of demand shock, but inventories are generally negative. The estimation of the linear quadratic model on data generated using the two versions of the generalized q-model shows that incentives to smooth production appear only when the firm is allowed to have negative inventories.     

A supply chain as a series of filters or amplifiers of the bullwhip effect

The bullwhip effect refers to the phenomenon of amplification and distortion of demand in a supply chain. By eliminating or controlling this effect, it is possible to increase product profitability reducing useless costs such as stock-out and obsolescence costs. The main focus of this work is to study a single-product serial supply chain in which a control parameter can switch the chain from a series of filters to a series of amplifiers of the bullwhip effect and to analyse how the optimal values of the parameters change when discontinuities in order policy are considered. Furthermore, it is also shown that the bullwhip itself it is not a good index of the chain's performance, because it does not consider the oscillations that occur in the inventories, which also may affect the supply-chain performance.     

Distribution contracts to support optimal inventory holdings under demand uncertainty

When suppliers produce products for which demand is uncertain, they face a problem of inducing downstream distributors to stock inventory levels that the suppliers prefer. This paper considers a wide array of alternative supply contracts, each of which consists of a mixture of constant per-unit wholesale prices, buy-back arrangements, and post sale payments contingent on sales made, such as revenue sharing or buybacks. We show that linear supply contracts specifying any combination of two of these three instruments can implement the vertical integrated outcome for a monopoly, thereby generating the supplier's preferred inventory configuration and price distribution. We extend our results to differentiated product oligopoly, demonstrating that each supplier obtains its preferred inventory configuration and price distribution, given the choices of its rival. Distributors choose optimal inventories from the suppliers' standpoint, even if suppliers do not know the distribution of demand uncertainty, and, given the perfect competition among distributors, all profits in the supply chain are captured by suppliers. Thus, suppliers are able to deal with demand uncertainty with remarkably little information about demand, and without the need to control dealer actions in detail. In particular, suppliers need not specify either dealer inventories or resale prices, but instead encourage distributors to order based on information in their possession and to set prices that generate desirable resale price dispersion.     

供需结构优化、分配结构演化与2035年共同富裕目标展望

共同富裕是社会主义的本质要求,中国推动经济社会发展,归根结底是要实现全体人民共同富裕。新发展阶段下中国既要优化供需结构以加快构建新发展格局,又要改善分配结构以全面贯彻新发展理念,而供需结构优化与分配结构演化又是紧密关联的。本文建立了一个包含供给结构、需求结构和分配结构的多部门动态一般均衡模型,将分配结构演化分解到供给结构与需求结构转型上,提出了需求结构通过影响供给结构进而影响分配结构的理论机制。本文对近三十年全球四十余个经济体劳动收入份额和技能溢价的演化进行了发展核算,展示了中国分配结构演化的特征事实、供需动因与国际比较。研究发现,中国分配结构演化道路具有一定的特殊性:一方面,劳动收入份额转为上升,供给侧(需求侧)最主要的推动力是持续提高的劳动密集型产业(消费品)的劳动密集程度;另一方面,技能溢价不断扩大,供给侧(需求侧)最主要的推动力是持续提高的产业内部(消费品)的技能密集程度;供需结构转型在其中也发挥了重要作用。本文还基于历史趋势定量预测了未来中国分配结构的演化趋势,为实现2035年共同富裕目标提供了现实依据与政策参考。     

A model for supply management of agile manufacturing supply chains

This paper addresses the configuration problem of Manufacturing Supply Chains (MSC) with reference to the supply planning issue. Assuming that the manufacturing system is composed of different stages, we present a technique for the strategic management of the chain addressing supply planning and allowing the improvement of the MSC agility in terms of ability in reconfiguration to meet performance. More in detail, we enhance a previous design method by some of the authors that employs digraph modeling and integer linear programming to optimally design the MSC. The original approach avoids supply chain disruption and stock out and, at the same time, can manage spare parts distribution. In order to take into account the level of demands and maximum production capacities with single/multiple sourcing, in this new formulation we introduce supplier capacity constraints. A case study is presented describing the optimal MSC configuration of an Italian manufacturing firm. The obtained results show that the design method provides managers with key answers to issues related to the supply chain strategic configuration and agility, e.g., choosing the right location for distributors and retailers for enhanced MSC flexibility and performance.     

An organizational perspective on inventory control: Theory and a case study

Inventory control is a well-covered area in literature. Nowadays, many concepts and techniques are available for effectively controlling inventories. Eminent examples are stochastic models to determine order quantities, techniques for forecasting demand and different kinds of ABC analysis. Remarkably enough, the theoretical backgrounds of these concepts and techniques show a great deal of similarity: they all stem from the field of operations management and operations research. Despite the value of the available concepts, such a one-sided approach has its limitations in practice. In this article it is argued that it is important to take a broader view when dealing with practical inventory control problems. First of all, an organizational perspective on inventory control is developed. The main idea behind this perspective is the importance of the organizational context of inventories. This means that in addition to the traditional points for attention, such as order quantities and replenishment strategies, other aspects need attention as well. They are, for example, the allocation of responsibilities and authorities regarding inventory management, the quality of inventory information and the relevant decision-making processes. These contextual factors as well as the traditional factors are mapped out and integrated into a framework to be used in solving practical inventory control problems. One of the main features of the framework is that it is useful in both analyzing and redesigning an inventory situation. Secondly, this article describes the results of a case study regarding the application of the organizational perspective to a practical inventory control problem. The central issue of the case study is the spare parts inventory of a missionary aviation organization in Africa. The case study shows that the organizational perspective on inventory control is very helpful in dealing with inventory control problems. It is illustrated that taking into account the organizational context of inventories, especially the responsibilities and authorities of the persons concerned, is a necessity to accurately understand inventory control problems. In addition, it is illustrated that the organizational perspective leads to a more appropriate redesign.     

价值网络重构、分工演进与产业结构优化

中国的产业结构优化在全球化背景下面临如何冲破"瀑布效应"的难题。本文建立了一个价值网络分工深化模型,认为发展中国家和发达国家的不同分工水平是产生瀑布效应的根本原因。发展中国家要突破瀑布效应实现产业结构优化,必须通过产业链、供应链和价值链重组建立自主发展型的价值网络,推进分工深化,才能摆脱价值链被俘获的处境,掌握产业结构优化的主导权。本土的产业链系统集成商在产业结构优化过程中起到关键作用,它需要根据企业的内外部环境选择具有一定分工迂回程度的产品,发挥分工带来的新比较优势,才能逐步实现资源和能力的积累,最终获得竞争优势。在产业结构优化过程中,政府政策与企业战略的协同非常重要。     

引进火电机组设备备品备件的管理

备品备件是缩短检修时间重要的物质基础。引进机组在建设过程中,加强备品备件的管理还可为国家节省外汇。为此就引进电站工程在建设过程中,引进设备备品备件的分类方法、引进数量、管理的实用制度、错供漏供备品的补供以及工程峻工后备品的移交等问题进行了分析讨论。     

Moderating the impact of global sourcing on inventories through supply chain management

In recent years, companies have paid growing attention to supply chain management at a global level. With regard to the upstream part of the supply chain, the need for better suppliers, the research into specific competences and concerns related to international competition have forced companies to improve their ability to cope with suppliers located in different countries around the world. The literature suggests that the geographical distance of suppliers should create higher inventory levels primarily because of longer and more uncertain lead times. However, as this paper aims to demonstrate, companies can limit this effect by means of specific investments in the supply chain and in their relationships with suppliers. The empirical analysis is based on data from the last edition of the International Manufacturing Strategy Survey (IMSS). The results show that companies performing global sourcing have invested in supply chain management (SCM) and that this has been helpful in keeping their inventories under control.     

回收数量受价格和随机因素影响的定价模型

假设在再制造闭环供应链中,集中决策者、第三方和制造商分别从最终客户那里回收废旧品,其回收数量受回收价格和随机因素影响,制造商对获得的旧部件进行再制造,如果旧部件不能满足生产需求,制造商将从新部件供应商那里以高价格采购新部件来补充短缺。本文按照废旧品回收的供应链成员不同,建立了3个定价决策模型,证明了每个模型最优解的存在性和唯一性,然后在特殊情形下进一步求得各模型最优解的解析式,最后用具体算例对模型进行了验证。     

集群供应链网络的联结模式与共治框架

集群供应链作为一类新型网络组织形式,是依托于产业集群又突破产业集群地域限制的供应链网络的集合体,集群供应链网络治理问题对集群竞争优势创造与集群持续发展有着重要作用。本文首先阐明了供应链网络与集群供应链网络的区别,进而对集群供应链网络的结构及类型进行了分析,在此基础上研究了集群供应链网络的联结模式,提出集群供应链网络共治的参与者、集群供应链网络共治框架体系及各参与主体在集群供应链共治中的作用分工,以期对集群供应链网络的治理活动起到借鉴作用。     

Schedule evaluation in unstable manufacturing environments

This paper provides a new approach to validate the feasibility of schedules of multiple-step mixed-model unstable manufacturing environments with different changeover times. Traditionally, continuous lines in a manufacturing process run the same sequence in order to minimize WIP inventory and lead time. Nevertheless, multiple reasons such as different product mixes or setup times can lead managers to run different sequences in continuous lines. Unfortunately, lack of reliability of supply and demand in these environments makes it difficult to manage product inventories and often leads to starvation due to the discoordination between the schedules of both lines. This approach is based on a new type of visual representation of schedules and an estimate the probability of starvation. It assumes stochastic supply and demand and a predefined schedule sequence based on batches of different sizes.     

随机需求下横向并购供应链网络整合优化策略研究

本文从系统优化视角,针对增设集散中心的横向并购供应链网络整合策略,利用变分不等式建立了随机需求下的整合优化模型。以市场链为主线,以供应链网络均衡理论为基 础,构建了以横向并购供应链网络活动总成本最小为目标的数学模型,通过转换成变分不等式采用改进的欧拉算法进行模型求解。通过数值算例进一步说明了模型的适用性和灵活性,得出了增设集散中心的并购整合策略能够降低供应链网络的平均运营成本的结论,通过对比不同市场紧密程度下产生的供应链网络平均成本协同效应,发现随着市场紧密程度的增加其协同效应更明显,为横向并购供应链网络整合优化提供理论依据与方法。     

The role of elasticity in supply chain performance

This paper develops a model that describes the performance of supply chains based on their elasticities of supply and demand. The model can be used to predict a supply chain's ability to respond to supply interruptions, cost increases, and demand shifts, while also quantifying the degree to which it is prone to the bullwhip effect. The bullwhip effect is a behavioral phenomenon by which orders are distorted as they are transmitted through the chain. Four types of supply chains are identified and their distinct operating characters are examined. The impact of rival firms and the impact of a decoupling point on supply chain performance are also examined.     

近期中国硫磺市场分析与预测

从我国经济景气状况,财政货币政策和产业政策等方面对硫磺市场的外部经济环境形势进行了分析,重点从市场供需、产业链方面就2010-2011年硫磺市场运行状况进行了研究。文章认为,我国对进口硫磺的依存度很高但无议价话语权,化肥产业结构以及出口政策的调整使得化肥产量增速下降,硫磺的需求相应减少,预计2011年下半年国内硫磺市场仍将处在僵持阶段。     

Optimization analysis of supply chain scheduling in mass customization

How to deal with the contradiction between scale production effect and customized demand is the key problem on studying mass customization (MC). When MC is operating in supply chain environment, on one hand, the excellent operating character of the supply chain will give conditions for solving this problem. On the other hand, it will bring out several complicated contradictions and increase the difficulties of the analysis and research on the supply chain operating and scheduling, so it is important to settle the contradictions. Based on our earlier work, the dominant contradictions of the supply chain scheduling in MC and the ways to relieve them are briefly summarized in this paper. A dynamic and multi-objective optimization mathematical model and the appropriate solving algorithm are set up by introducing these relieving methods into the operating process. It is pointed out that the characteristics of the model and algorithm cannot only reflect the unique operating requirements for this special production mode, but also merge with the thought of relieving the dominant contradictions. The feasibility of the model and algorithm in practical application to improve the scheduling efficiency and to settle the key problem mentioned above ultimately gets validated through the analysis of an application case we followed and through the algorithm simulation of a numerical scheduling case.     

Coordinated supply chain scheduling

A mixed integer programming approach is proposed for a long-term, integrated scheduling of material manufacturing, material supply and product assembly in a customer driven supply chain. The supply chain consists of three distinct stages: manufacturer/supplier of product-specific materials (parts), producer where finished products are assembled according to customer orders and a set of customers who generate final demand for the products. The manufacturing stage consists of identical production lines in parallel and the producer stage is a flexible assembly line. The overall problem is how to coordinate manufacturing and supply of parts and assembly of products such that the total supply chain inventory holding cost and the production line start-up and parts shipping costs are minimized. A monolithic approach, where the manufacturing, supply and assembly schedules are determined simultaneously, is compared with a hierarchical approach. Numerical examples modeled after a real-world integrated scheduling in a customer driven supply chain in the electronics industry are presented and some computational results are reported.