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.     

Inventory Management of a Plant Spare Parts Supply Chain

In spare parts industries, firms are dealing with a situation which is more and more uncertain due to the supply chain structure and variable demands. This paper presents a Bayesian approach to forecast demand and subsequently determine the appropriate parameter S of an (S - 1; S) inventory system for controlling plant spare parts. We apply the Bayesian approach in an innovative way to specify the initial prior distributions of the failure rates, using the initial estimates and the failure history of similar items. According to the proposed method, a lower base stock than the one currently used is sufficient to achieve the desired service level.     

维修备件基于AHP的ABC分类模型

针对ABC分类在设备维修备件管理中不足以区分重点备件的缺陷,将层次分析法与ABC分类相结合应用于设备维修备件的分类。将维修备件的易得性、关键性和经济性作为分类准则,通过ABC分类来求解备件对分类准则的权重,然后运用层次分析法计算备件的组合权重,再根据组合权重对备件进行ABC分类。该方法用于设备维修备件的分类可以快速有效地找出重点备件．提高备件管理工作的针对性和有效性。     

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.     

基于PDM的烟机企业零部件的分类管理

基于PDM零件分类管理的思想，结合许昌烟机公司的实际提出了在PDM环境下对零部件进行分类的方法及实现技术．实践证明，分类管理有助于实现零部件设计和工艺信息的查询与检索的计算机化，提高企业现有设计和制造资源的利用率．     

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。     

Advances in Computers

A mathematical model of a spare parts inventory control policy is constructed. The model is intended to apply to the case in which it is the policy to carry a maximum of one spare part in inventory. Under some relatively mild assumptions on the probability distributions of the time between demands for spare parts and of lead times, an overall cost function associated with any spare parts policy (SPP) is derived. An optimum SPP is defined to be one which minimizes the derived cost function. The minimization of the cost function leads to some objective criteria, stated in the form of a set of decision rules, to determine when to order a spare part. These rules are summarized at the end of Section 3. A brief discussion of these rules is contained in Section 4.     

Segmentation of continuous audio recordings of Carnatic music concerts into items for archival

Concert recordings of Carnatic music are often continuous and unsegmented. At present, these recordings are manually segmented into items for making CDs. The objective of this paper is to develop algorithms that segment continuous concert recordings into items using applause as a cue. Owing to the ‘here and now’ nature of applauses, the number of applauses exceeds the number of items in the concert. This results in a concert being fragmented into different segments. In the first part of the paper, applause locations are identified using time, and spectral domain features, namely, short-time energy, zero-crossing rate, spectral flux and spectral entropy. In the second part, inter-applause segments are merged if they belong to the same item. The main component of every item in a concert is a composition. A composition is characterised by an ensemble of vocal (or main instrument), violin (optional) and percussion. Inter-applause segments are classified into three segments, namely, vocal solo, violin solo, composition and thaniavarthanam using tonic normalised cent filter-bank cepstral coefficients. Adjacent composition segments are merged into a single item, if they belong to the same melody. Meta-data corresponding to the concert in terms of items, available from listeners, are matched to the segmented audio. The applauses are further classified based on strength using Cumulative Sum. The location of the top three highlights of every concert is documented. The performance of the proposed approaches to applause identification, inter-applause classification and mapping of items is evaluated on 50 live recordings of Carnatic music concerts. The applause identification accuracy is 99%, and the inter- and intra-item classification is 93%, while the mapping accuracy is 95%.     

A Risk‐based Approach to Managing Performance‐based Maintenance Contracts

The global trend towards performance‐based maintenance contracting has presented new challenges to maintenance service providers as they are compensated or penalized based on performance outcomes instead of time and materials consumed during maintenance service. The problem becomes more complex when uncertainties exist in reliability performance and maintenance activities of technical systems. In this paper, a general framework for managing performance‐based maintenance contract under risks is proposed. We illustrate our approach with an application in a multi‐echelon multi‐system spare parts control problem. Several different performance measures are considered and a probabilistic constrained optimization problem is formulated from the perspective of the service provider. Hybrid simulation/analytic heuristics are proposed to solve the problem based on the monotonic properties of performance measures. This approach is flexible and can be applied to a wide range of problems with similar properties. Numerical example shows that the probability of violating performance requirements is high if the risk is overlooked. We also provide guidelines on how to apply this approach in practice. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

A continuous‐time Markov chain model for redundancy allocation problem: An economic analysis

Reliability of an engineering system can be improved by investing on redundant (spare) parts. However, the cost‐efficiency of such an investment is a significant concern that needs to be taken into consideration in practice. To do so, a continuous‐time Markov chain (CTMC) model is presented in this paper to analyze the system's reliability by allocating redundant components. The developed model can also capture the system's repair and failure conditions by defining appropriate states in CTMC. Subsequently, the net present value (NPV) approach is utilized for a variety of scenarios to investigate the effectiveness of investment on spare parts using the break‐even point (BEP) analysis. Afterwards, a comprehensive analysis is carried out to examine the impact of input parameters including interest rate, initial cost of investment, and periodic profit on the decision making process to find the optimal number of spare parts.     

The failure intensity process and the formulation of reliability and maintenance models

A unified approach to the formulation of failure event models is presented. This provides a common framework for the analysis of both repairable and nonrepairable items, preventive as well as corrective maintenance, and it also applies for items with dormant failures. The suggested procedure is supported by a set of graphs, thereby identifying the significance both of the inherent reliability (i.e., hazard rate) and of the maintenance/repair policy. The definition/interpretation of various failure intensity concepts is fundamental for this approach. Thus, interrelations between these intensities are reviewed, thereby also contributing to a clarification of these concepts. The most basic of these; concepts, the failure intensity process, is used in counting processes (Martingales), and is the rate of failures at time t, given the history of the item up to that time. The suggested approach is illustrated by considering some standard reliability and maintenance models.     

二维保证下汽车维修备件动态库存控制策略

以汽车产品为例,针对失效率以时间或里程为计量单位的单位价值高、需求率低的不可修零部件,以未来销售预测为起点,依据二维保证政策的特点确定某时点处于保证时效内的汽车数量,基于产品可靠性对保证备件的需求进行预测,针对保证备件需求的特点,提出动态分段(Q,r)库存控制策略,通过案例验证了该库存策略可有效降低库存成本支出。     

In search for classification and selection of spare parts suitable for additive manufacturing: a literature review

This paper reviews the literature on additive manufacturing (AM) technologies and equipment, and spare parts classification criteria to propose a systematic process for selecting spare parts which are suitable for AM. This systematic process identifies criteria that can be used to select spare parts that are suitable for AM. The review found that there is limited research that addresses identifying processes for spare parts selection for AM, even though companies have identified this to be a key challenge in adopting AM. Seven areas for future research are identified relating to the methodology of spare parts selection for AM, processes for cross-functional integration in selecting spare parts for AM, broadening the spare parts portfolio that is suitable for AM (by considering usage of AM in conjunction with conventional technologies), and potential impact of AM on product modularity and integrality.     

An Additive Manufacturing Spare Parts Inventory Model for an Aviation Use Case

To maintain high service levels and mitigate long lead times, many enterprises hold large spare parts inventories. Using additive manufacturing (AM) for spare parts in aviation has been proposed previously but prior studies did not address system-specific lead time impacts. This article codifies lifecycle variables introduced by AM and presents an aviation case study. The variables highlight the value offered by AM over traditional methods. Specifically, the case study demonstrates that introducing up to 35% of AM parts to the spare parts inventory improves the system replenishment lead time by up to 33%, thus suggesting AM can be used to mitigate challenges related to spare parts management. This work also presents an approach to integrate AM into the spare parts inventory mix.     

基于剩余寿命预测的维修与备件订购联合策略优化

利用设备健康状态信息预测剩余使用寿命,并进行维修和备件订购决策以达到降低设备检修成本和备件成本的目的。针对单部件系统提出基于剩余寿命预测的维修与备件订购联合策略,其中维修决策遵循控制限原则,即根据系统退化量判断是预防性更换还是故障更换,同时基于历史退化信息预测系统剩余寿命,引入订货阈值判断是否订货。通过分析更换时刻备件状态确定所有可能更新事件,推导各事件发生概率进而计算各事件更新成本和更新长度,采用更新报酬理论构建最小化单位时间内期望费用的联合策略模型,设计离散事件仿真算法求解模型。最后,通过实例验证模型和算法,得到最小的单位时间内期望费用14.656 3,最优预防性更换阈值8,最优订货阈值1 000。     

Reducing the item number to obtain same-length self-assessment scales: a systematic approach using result of graphical loglinear Rasch modeling

The Revised Danish Learning Styles Inventory (R-D-LSI) (Nielsen 2005), which is an adaptation of Sternberg-Wagner Thinking Styles Inventory (Sternberg, 1997), comprises 14 subscales, each measuring a separate learning style. Of these 14 subscales, 9 are eight items long and 5 are seven items long. For self-assessment, self-scoring and self-interpretational purposes it is deemed prudent that subscales measuring comparable constructs are of the same item length. Consequently, in order to obtain a self-assessment version of the R-D-LSI with an equal number of items in each subscale, a systematic approach to item reduction based on results of graphical loglinear Rasch modeling (GLLRM) was designed. This approach was then used to reduce the number of items in the subscales of the R-D-LSI which had an item-length of more than seven items, thereby obtaining the Danish Self-Assessment Learning Styles Inventory (D-SA-LSI) comprising 14 subscales each with an item length of seven. The systematic approach to item reduction based on results of GLLRM will be presented and exemplified by its application to the R-D-LSI.     

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.     

Multiple criteria ABC inventory classification using two virtual items

ABC inventory classification is one of the most popular techniques for organisations to efficiently plan and control thousands of inventory items. Its traditional way is solely based on a single criterion; however, it has been recognised that multiple criteria need to be considered in practice. An alternative approach to multiple criteria inventory classification (MCIC) is proposed by using two virtual items and incorporating the TOPSIS. The proposed approach improves some previous allied methods as it provides a more reasonable and comprehensive performance index and a unique inventory classification without any subjectivity. Comparisons with other allied methods are illustrated through a case study.     

军械应急备件箱的设计

目的为满足当前军械应急维修保障需要,提升部队战斗力,研制一种新型的军械应急备件箱。方法通过部队调研得出军械应急备件箱的基本设计要求,运用机械原理和电子技术,重点从结构、功能和材料方面考虑,设计军械应急备件箱的技术方案。结果针对新研制的军械应急备件箱,分别进行了携运行能力、备件取用测试,测试结果表明军械应急备件箱携运行能力和备件取用便捷性均优于现有的备件箱。军械应急备件箱全箱采用了全封闭式结构,并分别在5,7,9,11 mm/min的降雨强度下进行了防水测试,均能保证备件盒内不渗水,说明该箱完全适用于在全天候条件下使用。结论经过试用认为,军械应急备件箱的研制弥补了现行部队军械维修时备件供应不精准且不便携行的缺陷,构建了合理的军械维修体系。