Development and analysis of mathematical and simulation models of decision-making tools for remanufacturing

This article presents decision-making tools for remanufacturing. The first decision-making tool was used to address inventory lot-sizing problems in a hybrid remanufacturing–manufacturing system with varying remanufacturing fraction. In this article, the new inventory lot-sizing model with variable remanufacturing lot sizes has been shown to exhibit better performance than the benchmark model with fixed remanufacturing lot sizes. The new inventory lot-sizing model is anticipated to become a valuable decision-making tool in companies that are planning to adopt remanufacturing. The second decision-making tool was applied to address a production and inventory planning problem in a remanufacturing system considering different remanufacturing policies for a given remanufacturing strategy. For a remanufacture-to-stock system with two quality remanufacturables groups four alternative policies were examined, a policy which specifies simultaneous processing utilising dedicated resources was shown to be the best policy to achieve a shorter remanufacturing cycle time. For a remanufacture-to-order system with two quality remanufacturables groups, the three relevant policies of the four alternative policies were examined, a policy which specifies sequential processing and switching between various quality remanufacturables groups was shown to be the best policy to achieve a shorter remanufacturing cycle time. The production and inventory planning simulation models in a remanufacturing system are expected to become significant decision-making tools in remanufacturing operations.     

Cost Allocation in Manufacturing–Remanufacturing Operations

For firms remanufacturing their products, the total life‐cycle costs and revenues from new and remanufactured products determine their profitability. In many firms, manufacturing/sales and remanufacturing/remarketing operations are carried out in different divisions. Each division is responsible for only part of the product's life cycle. Practices regarding transfer pricing across divisions vary significantly among companies, affecting the life‐cycle profit performance of the product. In this research, we identify characteristics of transfer prices that achieve the firm‐wide optimal solution. To this end, we consider a manufacturer who also undertakes remanufacturing operations and we focus on price (quantity) decisions. We determine that a cost allocation mechanism that allocates a portion of the initial production cost to each of the two stages of the product life cycle should be used. We also conclude that cost allocation should be implemented as a fixed cost allocation, where charges to the remanufacturing division should be determined independently of the actual quantity of units remanufactured.     

Take‐Back Legislation: Consequences for Remanufacturing and Environment

In the last two decades, many countries have enacted product take‐back legislation that holds manufacturers responsible for the collection and environmentally sound treatment of end‐of‐use products. In an industry regulated by such legislation, we consider a manufacturer that also sells remanufactured products under its brand name. Using a stylized model, we consider three levels of legislation: no take‐back legislation, legislation with collection targets, and legislation with collection and reuse targets. We characterize the optimal solution for the manufacturer and analyze how various levels of legislation affect manufacturing, remanufacturing, and collection decisions. First, we explore whether legislation with only collection targets causes an increase in remanufacturing levels, which is argued to be an environmentally friendlier option for end‐of‐use treatment than other options such as recycling. While increased remanufacturing alone is usually perceived as a favorable environmental outcome, if one considers the overall environmental impact of new and remanufactured products, this might not be the case. To study this issue, we model the environmental impact of the product following a life cycle analysis–based approach. We characterize the conditions under which increased remanufacturing due to take‐back legislation causes an increase in total environmental impact. Finally, we model the impact of legislation on consumer surplus and manufacturer profits and identify when total welfare goes down because of legislation.     

PRODUCTION SCHEDULING OF CONTINUOUS FLOW LINES: MULTIPLE PRODUCTS WITH SETUP TIMES AND COSTS

The problem of production planning and setup scheduling of multiple products on a single facility is studied in this paper. The facility can only produce one product at a time. A setup is required when the production switches from one type of product to another. Both setup times and setup costs are considered. The objective is to determine the setup schedule and production rate for each product that minimize the average total costs, which include the inventory, backlog, and setup costs. Under the assumption of a constant production rate, we obtain the optimal cyclic rotation schedule for the multiple products system. Besides the decision variables studied in the classical economic lot scheduling problem (ELSP), the production rate is also a decision variable in our model. We prove that our solutions improve the results of the classical ELSP.     

Multi-product lot scheduling with backordering and shelf-life constraints

In this paper, we revisit the economic lot scheduling problem (ELSP), where a family of products is produced on a single machine, or facility, on a continual basis. Our focus is on the determination of a feasible production schedule, including the manufacturing batch size of each item. We assume that total backordering is permissible and that each of the products has a limited post-production shelf life. Several studies examining this problem have suggested a rotational common cycle approach, where each item is produced exactly once every cycle. To ensure schedule feasibility, we resort to the technique of reducing individual production rates and allow the flexibility of producing any item more than once in every cycle, in conjunction with appropriate timing adjustments. In order to solve this more generalized model, which is NP hard, we suggest a two-stage heuristic algorithm. A numerical example demonstrates our solution approach.     

Multi-objective scheduling of two-job families on a single machine

This paper presents a preliminary analysis of the typical scheduling environment in semiconductor manufacturing involving multiple job families, and where more than one objective such as cycle time, machine utilization and the due-date accuracy needs to be simultaneously considered. In this study, the NP-hard problem of scheduling N independent jobs on a single testing machine with due dates and sequence-dependent setup times is addressed, where the multiple objectives are to minimize average cycle time, to minimize average tardiness, and to maximize machine utilization. A Pareto optimal solution, which is not inferior to any other feasible solutions in terms of all objectives, is generated combining the analytically optimal and conjunctive simulated scheduling approach. First, the machine-scheduling problem is modeled using the discrete event simulation approach and the problem is divided into simulation clock based lot selection sub-problems. Then, a Pareto optimal lot is selected using the compromise programming technique for multiobjective optimization at each decision instant in simulated time. With the help of a broad experimental design, this developed solution is then compared with common heuristic-dispatching rules such as SPT and EDD, which show better results for all the objectives over a wide range of problems. The developed scheduling method shows approximately 16.7% reduction in average cycle time, 25.6% reduction in average tardiness, and 21.6% improvement in machine utilization over the common dispatching rules, SPT and EDD.     

An adaptation of the EOQ formula for JIT quasi-pull system production

This research demonstrates for the first time that in a just-in-time (JIT) quasi-pull production environment, a model adapted from the Economic Order Quantity and made up of two specific formulas can be employed for calculating an optimised lot size. The assumptions of our model are: a low level of defects, and insignificant shortage backordering and failure of the equipment. JIT quasi-pull production is the state typically reached by many manufacturing companies because it is almost impossible to achieve zero set-ups and zero work-in-process (WIPs) even in the best Lean Production implementations. In this model, finished products are shipped at once in a JIT way. The two developed formulas are specialised: one for balanced stations/processes and the other for unbalanced stations; the formulas allow calculation of an optimised lot size. Several applications of the formulas have been tested and discussed through a case study. Findings demonstrated that the optimised quantity of a lot size has to be smaller than the customer’s daily demand for the product. Moreover, in case of unbalanced stations with long cycle times, the formula forces the company to reduce its set-up times and the cycle times. The new model will be of interest to practitioners who are seeking a way to balance the costs of set-ups and the cost of holding some WIPs and offers interesting avenues for new research.     

有限分布信息条件下MTO再制造系统提前期优化

在只知道零部件再制造时间有限分布信息（即一阶矩、二阶矩）条件下,基于MTO再制造策略研究由再制件和采购件组成的再制品的提前期问题,该问题被描述为一个矩问题。以最小化库存持有成本和缺货成本为目标建立min-max优化模型,在具有相同一阶矩、二阶矩的分布集合中寻找使最坏分布下的目标函数值最小的最优再制造提前期。最后通过算例进行了验证,求解结果与传统假设再制造时间服从正态分布、均匀分布得到的结果吻合较好,但本文的方法更符合生产实际,能保证在具有同样一阶矩和二阶矩的所有分布情况下的解的鲁棒性,对企业制定再制造计划、采购计划等具有现实的指导意义。     

A model for integrated production-packaging systems

The problem of determining the economic packaging frequency of jointly replenished items has received a lot of attention from researchers. This problem is usually encountered while packaging the products after completing manufacture. Nevertheless, production batch quantities certainly influence the manufacturing cycle time of products and hence the economic packaging quantities for jointly replenished items. Therefore, realizing the importance of the relationship between production batch quantities and packaging quantities     

面向并行制造的多生产单元协同调度研究

为提升多生产单元制造系统整体效率，在其系统内开展面向并行制造的协同调度研究，在考虑运输、换线等时间的基础上，构建多生产单元并行协同调度模型，采用并行分段协同遗传算法求解；在此基础上，将所研究协同调度方法应用于某复杂机电产品多生产单元制造车间，并与变批量调度与等批量调度比较。研究表明，所提的并行协同调度方法可以显著提升生产单元效率，提高生产单元设备和人员利用率。     

Simple policies in the economic lot scheduling problem with zero setup costs

The economic lot scheduling problem is analysed for the case when the cost of setups, but not their duration, is assumed to be zero. This would be the case when setups are performed by the machine operators, or when management's goal is holding-cost reduction. Theoretical results are presented describing when the common cycle solution of producing one lot of every item every cycle is optimal or near optimal. Computational results using simulated data are then presented which show that the common cycle solution is nearly optimal in a wide range of practical situations.     

Joint Life‐Cycle Dynamics of New and Remanufactured Products

Many products considered for remanufacturing are durables that exhibit a well‐pronounced product life cycle—they diffuse gradually through the market. The remanufactured product, which is a cheaper substitute for the new product, is often put on the market during the life cycle of the new product and affects its sales dynamics. In this paper, we study the integrated dynamic management of a portfolio of new and remanufactured products that progressively penetrate a potential market over the product life cycle. To this end, we extend the Bass diffusion model in a way that maintains the two essential features of remanufacturing settings: (a) substitution between new and remanufactured products, and (b) a constraint on the diffusion of remanufactured products due to the limited supply of used products that can be remanufactured. We identify characteristics of the diffusion paths of new and remanufactured products. Finally, we analyze the impact of levers such as remanufacturability level, capacity profile and reverse channel speed on profitability.     

基于产品质量内生的制造/再制造最优生产决策

从制造商的视角出发,将产品质量水平作为内生变量,并考虑质量水平对返回废旧产品的降级率的影响,分别讨论单寡头、双寡头非合作以及双寡头合作市场中,制造商最优制造/再制造决策策略.根据需求市场对产品价格和质量水平的敏感性,进行经济性分析,权衡制造商的制造/再制造的收益、生产成本,优化产品质量水平,帮助企业决定合理的再制造比例.研究结果显示:随着降级率的增大,制造商会降低再制造比例;制造商设置的降级率在不同模式下对利润与价格的影响是有差异的.     

经济批量排产问题的一种排产方法

针对经济批量排产问题假定生产可以在库存降为0之前开始,并且提出新的算法求产品的生产顺序。结果表明,该排产方法成本要低于其他2种常用的经济批量排产问题的方法,并且给出了算法的时间复杂性。     

奖惩机制下具竞争制造商的废旧产品回收决策模型

各国政府为保护环境加强了对废旧电器电子产品的回收再制造的管制。本文研究了两个制造商竞争情况下基于政府奖惩机制的制造商的废旧产品回收决策问题。具体研究时分两种情况:一种情况是两个制造商中只有一个回收再制造废旧产品,另一种情况是两个制造商都回收再制造废旧产品。研究表明:奖惩机制下回收再制造废旧产品的制造商的回收率提高;无论制造商是否回收再制造废旧产品,其新产品销售价均比无奖惩机制时低,奖惩机制对消费者有利;制造商竞争有利于奖惩机制引导制造商提高废旧产品的回收率;回收率随再制造率的提高而提高;无论另一个制造商回收再制造废旧产品与否,实施回收再制造制造商的利润随奖惩力度的提高而增加,随政府规定的目标回收率的提高而降低,且奖惩力度越大,降低幅度越明显。算例分析说明了上述结论的正确性。     

Models to explore remanufacturing as a competitive strategy under duopoly

Remanufacturing is a product recovery option that upgrades the quality of returns to “as-good-as-new” conditions. Remanufactured products cost less, and are sold with the same or better warranty as for new products. In this paper, we consider a duopoly environment with two manufacturers in direct competition selling their respective new products on the primary market. Specifically, we address the question: In case one manufacturer decides to remanufacture and sell remanufactured products on the price-sensitive secondary market, will it get a competitive advantage over the other manufacturer? We develop theoretical models for a single period and two periods, and show that under the stated assumptions, remanufacturing is almost always more profitable than when there is no remanufacturing. Although remanufacturing may cannibalize new product sales, the combined profitability and market share of the (re)manufacturer on account of new and remanufactured product sales improve over new product sales only. For the competitor, we get mixed results. In some situations, its profitability improves; in some others, it worsens. We also conduct sensitivity analyses with respect to the substitution parameters, price-sensitivity of the secondary market, rate of return of used products (cores), relative market shares of the manufacturers, and relative sizes of the primary and secondary markets. We conclude the paper with managerial implications and directions for future research.     

A Comparison between Basic Cyclic Scheduling and Variable Cyclic Scheduling in a Two‐stage Hybrid Flow Shop

In this paper the impacts of two types of repetitive scheduling systems on the makespan in a two‐stage hybrid flow shop, which consists of one machine in the first stage and multiple process lines in the second stage, are compared. First, we analyzed, through a simulation, how the makespan is affected by the setup frequency and sequencing rules for products under two types of scheduling systems: One is repetitive scheduling with only one batch per product family per scheduling cycle (basic cyclic scheduling system). The other is repetitive cyclic scheduling with various batches per product family per scheduling cycle (variable cyclic scheduling system). Second, we compared which scheduling system is superior under various manufacturing situations. The following points were noted. (1) The superior scheduling system can be shown by a two‐dimensional diagram of the setup frequency and the imbalance in workload for processing among process lines in the second stage. (2) Variable cyclic scheduling is superior in comparison with basic cyclic scheduling when there is a large imbalance in the workload to be processed among process lines in the second stage, or the workload in the second stage is larger than that in the first stage. The result of this research provides guidelines for selecting which scheduling system should be adopted.     

闭环供应链上的回收激励契约设计与政府补贴再制造政策的优化

废旧工业产品的回收再制造活动具有较大的正向外部经济特性,常常导致企业从事该项活动的动力不足。从节约资源和保护环境的目的出发,各国政府大都制定了给予补贴以鼓励回收再制造活动的政策。而且新产品和再制造产品一般具有一定的感知价值差异,可能会影响到再制造成本优势的发挥。将政府也作为一个决策主体,建立了以政府为领导者、制造商和再制造商、回收商为跟随者的三级非线性闭环供应链上的Stackelberg主从博弈模型,其中嵌套了基于委托代理关系分析基本技术框架的再制造商对回收商回收努力的最优激励契约。分析求解了政府和制造商、再制造商等的最优决策。政府的补贴政策将有效提高再制造品的竞争优势,同时有效降低废旧产品的掩埋等处理成本,有利于生态环境的保护。政府最优补贴下再制造商对回收商的最优激励机制设计可以有效提高废旧工业品的回收再制造效率。新产品和再制造产品的相互替代程度将间接影响到政府的最优补贴决策。同时通过数值分析得到再制造的比较成本优势对闭环供应链决策的影响。可供政府有关部门在政策制定以及闭环供应链上的企业决策时参考。     

MANAGING CYCLIC INVENTORIES

Cyclic inventory is the buffer following a machine that cycles over a set of products, each of which is subsequently consumed in a continuous manner. Scheduling such a machine is interesting when the changeover times from one product to another are non‐trivial—which is generally the case. This problem has a substantial literature, but the common practices of “lot‐splitting” and “maximization of utilization” suggest that many practitioners still do not fully understand the principles of cyclic inventory. This paper is a tutorial that demonstrates those principles. We show that cyclic inventory is directly proportional to cycle length, which in turn is directly proportional to total changeover time, and inversely proportional to machine utilization. We demonstrate the virtue of “maximum changeover policies” in minimizing cyclic inventory—and the difficulty in making the transition to an increased level of demand. In so doing, we explicate the different roles of cyclic inventory, transitional inventory, and safety stock. We demonstrate the interdependence of the products in the cycle—the lot‐size for one product cannot be set independently of the remaining products. We also give necessary conditions for consideration of improper schedules (i.e., where a product can appear more than once in the cycle), and demonstrate that both lot‐splitting and maximization of utilization are devastatingly counter‐productive when changeover time is non‐trivial.     

不同渠道权力结构下的S-M两级闭环供应链绩效分析

与传统正向供应链相比,闭环供应链关注对消费阶段后的废旧产品进行回收再制造,从而减少环境污染、降低资源消耗,对推动制造业的可持续发展具有非常重要与深远的意义。为了探讨产品再制造战略对闭环供应链中成员企业的影响,本文采用博弈论对一个供应商和一个制造商构成的S-M两级闭环供应链进行研究,着重分析供应商强势、制造商强势以及供应商和制造商双方势力均衡时的定价策略和供应链系统绩效。研究结果表明:当实施产品再制造战略时,产品的销售价格降低、产品的市场销量增加,零部件的批发价格则上涨。从成员企业个体来看,再制造战略总是有助于制造商获得更多额外收益,而对供应商的影响效应则与供应商在渠道中的权力地位有关,处于强势地位的供应商可以通过大幅提高零部件批发价格的方式来保证自己从再制造中获益,而处于弱势地位的供应商则有可能遭受利益损失。从系统整体绩效来看,再制造战略具有提升供应链系统整体赢利水平的积极作用,但是供应商和制造商之间的权力结构会影响再制造的经济价值。具体而言,供应商和制造商势力均衡时的供应链绩效最优,其次是制造商主导的供应链,最差的是供应商主导的供应链。