The distribution of spare parts

This paper will report some results from an overall research project on the ‘Stock Control of Spare Parts’, concentrating on the distribution tasks of the manufacturer in providing product support for his products in the field. After reviewing the nature of the problem, the first section of the paper will be devoted to consideration of the initial provisioning problem of the manufacturer supplying a new capital equipment product. The second section will deal with the problem of forecasting demand for spare parts where the original equipment has gone out of production, but the manufacturer undertakes to continue product support for a period of time. The illustration of this problem is taken from the motor industry where determining all-time requirements and the consequent ordering pattern is considered.     

On the demand distributions of spare parts

Spare parts have become ubiquitous in modern societies, and managing their requirements is an important and challenging task with tremendous cost implications for the organisations that are holding relevant inventories. Demand for spare parts arises whenever a component fails or requires replacement, and as such the relevant patterns are different from those associated with ‘typical’ stock keeping units. Such demand patterns are most often intermittent in nature, meaning that demand arrives infrequently and is interspersed by time periods with no demand at all. A number of distributions have been discussed in the literature for representing these patterns, but empirical evidence is lacking. In this paper, we address the issue of demand distributional assumptions for spare-parts management, conducting a detailed empirical investigation on the goodness-of-fit of various distributions and their stock-control implications in terms of inventories held and service levels achieved. This is an important contribution from a methodological perspective, since the validity of demand distributional assumptions (i.e. their goodness-of-fit) is distinguished from their utility (i.e. their real-world implications). Three empirical datasets are used for the purposes of our research that collectively consist of the individual demand histories of approximately 13,000 SKUs from the military sector (UK and USA) and the Electronics Industry (Europe). Our investigation provides evidence in support of certain demand distributions in a real-world context. The natural next steps of research are also discussed, and these should facilitate further developments in this area from an academic perspective.     

Simulation of an integrated age replacement and spare provisioning policy using SLAM

This paper presents a SLAM simulation model for determining a jointly optimal age replacement and spare part provisioning policy. The policy, referred to as a stocking policy, is formulated by combining age replacement policy with a continuous review (s, S) type inventory policy, where s is the stock reorder level and S is the maximum stock level. The optimal values of the decision variables are obtained by minimizing the total cost of replacement and inventory. The simulation procedure outlined in the paper can be used to model any operating situation having either a single item or a number of identical items. Results from a number of case problems specifically constructed by 5-factor second order rotatory design have been presented and the effects of different cost elements, item failure characteristics and lead time characteristics have been highlighted. For all case problems, optimal (s, S) policies to support the Barlow-Proschan age policy have also been determined. Simulation results clearly indicate the separate optimizations of replacement and spare provisioning policies do not ensure global optimality when total system cost has to be minimized.     

Failure analysis of an EDM machined mold-printing die used for the production of truck spare parts

A company produces truck wheel covers as spare parts for the local market. The production of these parts is based on a progressive die performing consecutive forming and selective cutting stages throughout the initial circular steel sheet. The failure occurred to the final stage of manufacturing, as the die marks, by mold-printing, the assembly configuration of the wheel cover onto the wheel rim. The paper presents a thorough failure analysis of the broken tool. The investigation includes preliminary examination, hardness measurements and chemical analysis. In depth microscopic examination was carried out using stereoscope and optical and electron microscopy. The failure mechanism was investigated from macroscopic and microscopic perspective and conclusions regarding the crack initiation and propagation were conducted and analyzed. The causes that led to the total fracture were discussed. The design of the tool and improper surface roughness are considered to be the main causes of the failure. Some complementary recommendations were proposed so to enhance the production rate of the specific tool.     

Optimal service parts contract with multiple response times and on-site spare parts

This study examines user outsourcing of spare parts management to vendors through a service contract. The user’s selection of a fixed-price service parts contract is formulated as a stochastic integer programming model that decides multiple response times and on-site spare parts, while considering component breakdown with uncertain failure rates. We analytically derive the optimality conditions for the continuous case and subsequently design an efficient algorithm. Numerical illustrations and analyses are conducted to evaluate decisions under various scenarios. Our analysis shows that when both failure rate and expedited contract cost are high, coupled with low part cost, users would prefer the purchase of spare parts for all components to expedited contracts. A fixed-price expedited contract has a lower marginal cost with respect to failure rate than a fixed-price next day contract and a usage-based contract. We also examine inventory behaviour for a single part, multiple types of parts, and multiple groups of parts. It is shown that there is a cost-saving pooling effect in spare parts for identical items, which significantly raises the likelihood of having on-site stored parts. The problem becomes more complex for multiple items, reflecting bundling effects between items for a given contract.     

备件消耗预测与备件储备定额的确定

只有准确的预测备件消耗趋势，才能合理确定备件储备定额，降低生产成本。用“趋势修正移动平均预测法”来预测备件消耗趋势，从而确定备件储备定额，可以节省一半以上的费用及流动资金。     

Modelling and solving spare parts supply chain network design problems

Spare parts are key operational assets in order to minimise unexpected equipment downtimes that may significantly impact a company’s results. The spare parts supply chain network supports the entire spare parts operations management and it is essential to achieve the planned goals. However, most of the traditional literature on spare parts management has not focused on the underlying supply chain network. Thus, this paper studies the integration of supply chain network design and control with traditional spare parts management. In particular, a generic network optimisation modelling structure is proposed, with simultaneous optimisation of warehouse locations and inventory control decisions, allowing minimising the total costs associated with the spare parts supply chain network. The generic model is specified based on three inventory control policies widely employed in the industry, which are suitable for managing a great variety of spare parts, i.e. (s, Q), (R, s, S) and (S-1, S). Furthermore, a solution approach is proposed based on Generalised Benders Decomposition. Finally, numerical results from a real-world application case in the process industry are shown and discussed.     

Sensor-driven prognostic models for equipment replacement and spare parts inventory

Accurate predictions of equipment failure times are necessary to improve replacement and spare parts inventory decisions. Most of the existing decision models focus on using population-specific reliability characteristics, such as failure time distributions, to develop decision-making strategies. Since these distributions are unaffected by the underlying physical degradation processes, they do not distinguish between the different degradation characteristics of individual components of the population. This results in less accurate failure predictability and hence less accurate replacement and inventory decisions. In this paper, we develop a sensor-driven decision model for component replacement and spare parts inventory. We integrate a degradation modeling framework for computing remaining life distributions using condition-based in situ sensor data with existing replacement and inventory decision models. This enables the dynamic updating of replacement and inventory decisions based on the physical condition of the equipment.     

Integrated planning of spare parts and service engineers with partial backlogging

OR Spectrum - In this paper, we consider the integrated planning of resources in a service maintenance logistics system in which spare parts supply and service engineers deployment are considered...     

Spare parts management for technical systems: resupply of spare parts under limited budgets

In this paper, we study the operational availability of a complex technical system consisting of several components. The components are subject to breakdowns, and hence for each component a limited number of spare parts are held in stock. If a system's component fails and it can not be replaced immediately, due to a lack of spares, the system becomes unavailable until a new component is installed. Failed components are disposed of and hence, to keep the spare parts stock at an appropriate level, new components have to be purchased. We assume that only a limited annual budget is available for procurement, while any further procurement requires a considerable lead time. We investigate at an aggregate level what budgets are needed to attain a target availability level for the system. In addition, we develop various operational strategies for spending the annual budget during each year. Numerical results indicate that the so-called Balance Focussed strategy provides the best results in terms of system availability as a function of time.     

On the implementation of a control-based forecasting system for aircraft spare parts procurement

The implementation of a new control-based forecasting system (SDF) in 1989-1991 at the Aviation Supply Office, Philadelphia, Pennsylvania, is documented. The philosophy, experience, principles and formulas are presented with results from three implementations.     

基于随机提前期的备件携行量计算方法

舰艇出海执行任务期间，需要携行一定种类和数量的物资自给。文中研究了这种单级供应条件下，如何确定备件最优携行量的问题。建立了以服务水平为目标，以资源为约束的目标规划模型，模型考虑了随机提前期和备件重要度。提出一种基于边际效费比的增量法用于求解这个模型。最后，给出一个算例并得到了一些结论。