CONFORMANCE QUALITY AND REPLACEMENT COSTS UNDER WARRANTY

In this paper, I investigate the impact of the conformance quality of a durable product on manufacturer's and user's replacement costs while the product is under warranty. I first relate conformance quality to reliability and then examine its effects on warranty costs to manufacturer and customer under both pro-rata and free-replacement warranties. In particular, I show that the reduction in customer's cost is generally contingent on more stringent quality improvement than the reduction in manufacturer's costs. I also discuss the value of inspection, and I present an application based on real data.     

风险质检行为下的模糊生产-库存决策

本文研究在风险质检行为下需求与生产率具有模糊属性的由一个制造商与一个零售商构成的生产-库存问题。在假设制造商生产的产品存在质量缺陷,零售商在质检过程中存在质检风险的基础上,分别建立了需求模糊下的生产-库存总成本模型,需求与生产率模糊下的总成本模型,运用符号距离法进行了逆模糊化处理,将模糊化的生产-库存总成本转化为确定性成本。证明了两类情形下的总成本均是关于最优订购量与最优缺货量的联合凸函数。数值分析结果表明：随着期望缺陷率的增加,最优订购量增加,最优缺货量减少,最优成本增加,且最优成本增加的速度越来越快。一类质检风险增大引起总成本增加,二类质检风险增大引起总成本减少。最优订购策略对质检一类风险敏感,对质检二类风险不敏感。     

When to Offer Lower Quality or Remanufactured Versions of a Product

We investigate the profitability of adding a lower quality or remanufactured product to the product portfolio of a monopoly firm, both in single‐period and steady‐state settings. Consumer behavior is characterized by a deterministic utility function for the original product and a nonlinear relative utility function for the lower quality product. We find a threshold for the cost of the low‐quality product below which it is optimal to add it to the firm's portfolio, and show that while a cost advantage is necessary to make the lower quality offering profitable under linear or convex relative utility functions, market segmentation alone can justify the addition of the lower quality product under concave relative utility functions. In particular, we characterize (i) the new product cost under which it is optimal to offer a lower quality version of the product even if it is as costly to produce as the original product; and (ii) the weighted average of new and remanufactured product costs in the steady state under which it becomes cost effective to offer new products under the remanufactured label. Finally, we also identify the maximum possible profits from customer segmentation and the form of the relative utility function that achieves them. We discuss the implications for the common marketing practices of branding and generics.     

An optimal design for process quality improvement: modelling and application

Existing research works on process quality improvement focus largely on the linkages between quality improvement cost and production economics such as set-up cost and defect rate reduction. This paper deals with the optimal design problem for process improvement by balancing the sunk investment cost and revenue increments due to the process improvement. We develop an optimal model based on Taguchi cost functions. The model is validated through a real case study in automotive industry where the 6-sigma DMAIC methodology has been applied. According to this research, the management can adjust the investment on prevention and appraisal costs on quality improvement that enhances process capability, reduces product defect rate and, as a result, generates remarkable financial return.     

Economic Production Lot Sizing with Periodic Costs and Overtime*

Traditional approaches for modeling economic production lot‐sizing problems assume that a single, fixed equipment setup cost is incurred each time a product is run, regardless of the quantity manufactured. This permits multiple days of production from one production setup. In this paper, we extend the model to consider additional fixed charges, such as cleanup or inspection costs, that are associated with each time period's production. This manufacturing cost structure is common in the food, chemical, and pharmaceutical industries, where process equipment must be sanitized between item changeovers and at the end of each day's production. We propose two mathematical problem formulations and optimization algorithms. The models' unique features include regular time production constraints, a fixed charge for each time period's production, and the availability of overtime production capacity. Experimental results indicate the conditions under which our algorithms' performance is superior to traditional approaches. We also test the procedures on a set of lot‐sizing problems facing a national food processor and document their potential economic benefit.     

考虑故障停机的生产控制与维修计划联合决策模型

通过生产控制与维修计划协同决策,降低生产成本。首先描述生产过程,分析各项费用。其次,建立了考虑生产过程失控、故障率和故障停时间的生产过程控制、生产计划优化和维修管理联合优化决策的模型。通过模型求解,联合制定出生产过程检查策略、生产计划（经济生产批量、生产批次）以及维修计划（PM间隔期）,实现单位时间内总费用最低的目标。再次,案例研究,分析生产过程失控、故障率和故障停机时间对于经济生产批量、生产过程检查策略和生产系统维修计划的影响。该模型从理论上解决了生产过程控制、生产计划优化和维修管理联合优化决策难题,对于指导企业制定生产计划和生产系统的检修计划,进而提高产品质量、降低生产成本、确保准时交货都具有指导意义和实用价值。     

ECONOMIC PROCESS CONTROL UNDER UNCERTAINTY

The future of the global industry lies in the continuous improvement of both products and processes, a renewed commitment to competition, and an aggressive approach to satisfying customers needs in quality, quantity, and timing. In quality management, the degree of customer satisfaction for a given product may be measured in the form of the loss to society. This loss is formulated as a function of the deviation from the target for each of the product's quality characteristics. The greater the variability of uncontrolled factors during manufacturing or production the larger will be that loss. In this paper, we develop a form of the loss function that takes into account the variability of a production process, the decision loss, and the costs of sampling and inspection. Specifically, we consider monitoring a production process, which may undergo continuous mean shift and variance deterioration during a production run. We then examine decision rules for continuing production or stopping and adjusting the production process.     

两级供应链产品质量控制契约模型分析

基于博弈论和委托代理理论,研究在两级供应链中如何进行质量控制契约设计的问题。建立生产商和购买商的期望收益函数模型,生产商对其生产过程投资水平进行决策并确定其产品质量预防水平;购买商进行质量评价决策并确定其产品质量检验水平。生产商存在降低其生产过程投资水平的道德风险问题,在生产过程中将"削减投资",购买商为激励生产商提高其生产过程投资水平将支付"信息租金"的成本。购买商在进行产品质量检验决策时,存在夸大产品质量缺陷率的道德风险问题,在产品质量检验过程中将"过度检验"。运用最优化原理,求解生产商的最优生产过程投资水平、产品质量预防水平和价格折扣额与购买商的最优质量检验水平和外部损失分摊比例,并进行了算例分析,结果表明:当生产商提高其生产过程投资水平时,其质量预防水平将显著增加,购买商的质量检验水平将显著下降;随着购买商质量检验水平的提高,生产商所提供的价格折扣额先增大后减少,生产商所承担的外部损失分摊比例将会下降,其期望收益增加,购买商的期望收益将会减少,供应链联合期望收益将呈现"倒U"型,求解了期望收益的最大值及各契约参数的值,结果证明所提出的质量控制契约模型是可行的。     

Quality-related costing: Findings from an industry-based research study

With the support of the Science and Engineering Research Council and the cooperation of several manufacturing organisations the authors have carried out a major study of the collection and use of quality-related costs in manufacturing industry. The paper summarises the main limitations and omissions of the literature on quality costing and provides guidance on the most authoritative reading on the subject. Experience acquired whilst carrying out the investigations at collaborating companies is reviewed and some of the major issues are discussed, including definitions of quality cost categories and elements, collection and reporting of quality cost data and the uses of quality costs. Alternatives are suggested to (or may be used to complement) the usual prevention-appraisal- failure approach to categorisation of quality-related costs which is so firmly entrenched in both management thinking and the literature on the subject.     

DEVELOPING SOPHISTICATED QUALITY IMPROVEMENT APPROACHES THROUGH BUSINESS-ACADEME COLLABORATIONS: INTRODUCTION TO THE SPECIAL ISSUE

The pursuit of better performance has led to a number of business-academe collaborations. These collaborators have developed a number of sophisticated approaches that go far beyond such traditional simple methods as benchmarking against the best company, Ishikawa diagrams on feedback and control, Pareto diagrams, incentive systems based solely on output or quality, standard process control charts, and separate treatment of control charts and product inspection. The authors in this special issue report on approaches like benchmarking industrial performance through industry studies; the use of an artificial-intelligence statistical-tree growing method to analyze complex customer service data; an incentive system based on the total quality management (TQM) concepts of continuous improvement, teamwork, adaptation to change, and a focus on customer satisfaction; and integration of product inspection and process control. Because of the continuing widespread interest in TQM, there is an opportunity to take stock of how successful TQM initiatives have been and how we should consolidate and further extend the knowledge in TQM. Two of the papers report on the gap between what organizations espouse as TQM and what they actually implement and on the literature on TQM.     

Capacity Investment and Product Line Decisions of a Multiproduct Leader and a Focus Strategy Entrant

In this article, I investigate the capacity investment cost conditions where a multiproduct market leader may respond to a focus strategy entrant by using different strategies such as changing the product mix, production volumes, quality levels, and/or by investing in more capacity. The products offered in the market are quality differentiated and customers are heterogeneous in their willingness to pay for quality. The capacity investment costs of the two firms (i.e., the leader and the entrant) may also be different. The classical Stackelberg model predicts that an incumbent does not change its position in response to entry. However, when heterogeneous customer base, product differentiation, and capacity costs are taken into consideration, I find that the leader with a low capacity cost may choose to expand its product line and increase its production. The leader with low capacity cost may introduce a product that it was holding back when the entrant has to bear the high‐capacity cost and cannibalization threat is relatively small. Nevertheless, the extent of production volume strategies reduces as the capacity cost increases for the leader. I also find that when the leader has the power to set the industry standards by deciding the quality levels, as a response to a high‐quality focused entrant, the leader increases both levels of quality and production of the low‐quality product. Moreover, when the capacity investment cost is high for both the entrant and the leader, I find that market prices may increase with entry.     

THE ESTIMATION OF LINEAR PRODUCTION FUNCTIONS HAVING MULTICOLLINEAR INPUTS

In this paper linear production functions with highly correlated independent variables are estimated. Because many production processes require the use of inputs in fixed proportions, multicolinearity is usually a serious problem. This is usually the case when one attempts to estimate a linear or Cobb-Douglass (in log linear form) production function. Estimates of the marginal products of a linear production function are obtained by employing the first order conditions of the output maximizing solution given a cost constraint. Parameter estimates are determined for the case where the input costs are constants. The general case, where the input prices are functions of utilization levels, is delineated.     

Equilibrium Joining Strategies and Optimal Control of a Make‐to‐Stock Queue

We consider a make‐to‐stock, finite‐capacity production system with setup cost and delay‐sensitive customers. To balance the setup and inventory related costs, the production manager adopts a two‐critical‐number control policy, where the production starts when the number of waiting customers reaches a certain level and shuts down when a certain quantity of inventory has accumulated. Once the production is set up, the unit production time follows an exponential distribution. Potential customers arrive according to a Poisson process. Customers are strategic, i.e., they make decisions on whether to stay for the product or to leave without purchase based on their utility values, which depend on the production manager's control decisions. We formulate the problem as a Stackelberg game between the production manager and the customers, where the former is the game leader. We first derive the equilibrium customer purchasing strategy and system performance. We then formulate the expected cost rate function for the production system and present a search algorithm for obtaining the optimal values of the two control variables. We further analyze the characteristics of the optimal solution numerically and compare them with the situation where the customers are non‐strategic.     

MANUFACTURING QUALITY,RELIABILITY AND PREVENTIVE MAINTENANCE

We consider an important topic from the traditional quality literature-the impact of conformance quality of a manufactured product on the preventive maintenance costs to downstream users of this product. Folk wisdom supports the notion that higher conformance quality translates into lower maintenance costs (as well as other components of life-cycle costs) for these users. We examine this proposition in some detail on the basis of a failure-time model that relates conformance quality to reliability. We consider both repairable and nonrepairable items that are maintained by a block-replacement or a minimal-repair strategy. In addition to maintenance cycles and costs, we discuss the value of information to the user as to the actual production quality, and the value of inspection.     

The optimum targeting for a single filling operation with rectifying inspection

One of the important issues in quality control is finding the optimal target value for a process under various inspection policies. Researchers have considered various aspects of this problem with 100% inspection and with quality sampling plans. In this paper we consider the problem of targeting the set point when rectifying inspection is used. We develop a model for this problem and propose a scheme for solving it. We also provide a numerical example.     

Quality Testing and Product Rationing by Input Suppliers

Quality testing by suppliers has significant ramifications for downstream supply chain participants and retail consumers. This article focuses on such implications accounting for the fact that suppliers often enjoy discretion in quality testing and reporting. Under a discretionary testing and reporting environment, we show that a supplier can improve the market's perception of product quality by engaging in self‐imposed production cuts. Production cuts dampen supplier incentives to engage in excessive quality testing, putting the supplier and the market on a more equal information footing. This reduces the market's need to skeptically discount product quality to protect itself. The improved market perception, then, reduces quality testing demand, introducing cost savings. The result that costly production cuts can improve quality perceptions indicates that the groundwork for influencing market perceptions may have to be laid upfront, even prior to acquiring private information, providing a contrast to routine signaling models.     

Process improvement by variance reduction for a single filling operation with rectifying inspection

Recently, there has been a great interest in the economics of quality control. Process mean targeting is one of the quality control problems which has attracted many researchers. Many papers have been written on finding the optimal mean setting of the process, but very few papers have considered the value of variance reduction. In this paper, we consider a single filling operation with rectifying inspection. We study the effect of the variance on the process performance. We analyse the cost saving which results from reduction in the process variance. We also provide a numerical example.     

基于SRFML-Lift的流程制造产品质量状态监测

对流程制造型企业而言,产品质量状态的监测精度直接影响了企业的生产与运营成本。面对流程工业的多变量监测要求和数据不均衡性,以往研究主要采取局部建模策略或多输出模型,存在特征选择偏差和分类精度不高的问题。对此,本文设计了一种结合SRFML特征选择和Lift学习策略的质量状态监测模型,通过共享不同目标之间的信息以期提升模型的监测效果。首先,根据ReliefF过滤机制,引入重采样赋权思想对工业特征的选择过程进行优化(SRFML);然后,将选择结果作为Lift学习框架的输入,通过类属属性学习方式重塑各待监测特性的特有关联属性;最后采用多个SVM分类器进行训练,得到各目标的质量状态结果。结果表明,本文构建的SRFML-Lift充分学习了原始特征的关键信息,与其他组合策略相比,对质量状态的监测效果更佳,可应用于流程工业的生产管理实践。     

The Influence of Quality Inspections on the Optimal Safety Stock Level

Due to yields of less than 50% during the production of curved glass for the displays on their new cell phone series, Samsung has to deal with higher than expected production costs of several million dollars. Where there is random yield, production costs as well as holding costs can be reduced by introducing quality inspections, in which defective items are discarded before further production. To achieve the greatest cost savings, it is important to determine the optimal number and positions of these inspections across the production process which, due to several influencing parameters, is not simple. We show how the positions of inspection within a production process influence the safety stock level that is required to buffer against uncertainties due to demand and yield randomness. Our approach is the first one, combining decisions about the number and positions of inspections with inventory control strategies in a warehouse. We achieve a maximum safety stock reduction of more than 30% in our examples, which can be even larger depending on the parameter setting. For a company like Intel, reporting inventories for finished goods of nearly 1.5 billion dollars in the 2014 annual report, this allows for significant savings.     

Manufacturing feature-based cost management system: a case study in Brazil

Feature costing is a topic of recent discussion related to cost management systems (CMSs) aimed at understanding how product features influence production process costs. It raises as a key issue in mass customisation environments where a single product model can present hundreds of menu options. In this study, we explore the concept of feature costing beyond the use of activity-based costing (ABC). We propose a CMS based on features and common elements as costing objects instead of products. In our model, we use the unit of production effort method to organise the direct manufacturing costs, ABC method to address the indirect cost and the standard methods to compute raw materials costs. We illustrate the method in the production of bus seats in a Brazilian manufacturing company. This study gives different perspectives to the international academic community on the use of a different CMS used by many Brazilian companies.