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Background: Exploring the impact of combining Industry 4.0 technologies and Lean Manufacturing tools on organizational performance has been a popular topic in recent years. Design/Methodology/Approach: We propose a novel Smart and Sustainable Manufacturing System (SSMS) to provide management insights related to social impact, economic performance, and environmental impact. Some tools called Dynamic Lean 4.0 tools, such as Sustainable Value Steam Mapping (VSM), Extended Single Minute Exchange of Die (SMED), and Digital Poka-Yoke, are presented as outputs of synergistic relationships that optimize production processes. Originality/Research gap: There are few studies on the application of SSMS. This work presents a case study, aiming to fill this gap. A case study of vacuum degassing equipment fabrication is presented to demonstrate the improvement of utilizing the Define-Measure-Analyze-Improve-Control (DMAIC) method with Digital Poka-Yoke. Key statistical results: The implementation of this project increased the process capability index, Cpk, from 1.278 to 2. Practical Implications: It was concluded that the company successfully implemented a smart and sustainable manufacturing system, and created a safer working environment and new job opportunities, while increasing production yield from 99.44% to 100%, improving worker utilization, and directly saving NT$68,000. Limitations of the investigation: This paper is the use of a single case study. More applications of Dynamic Lean 4.0 tools in SSMS should be explored.

Global greenhouse gas emissions must be reduced to achieve net-zero carbon emissions. One of the solutions for the reduction of greenhouse gas emissions is the adoption and transition from conventional vehicles to electrical vehicles (EVs). Previously, most research on EVs have been from a consumer adoption perspective, few of them are from industry transition and consumer adoption perspectives simultaneously. This also highlights the importance of SDG 12 (responsible for consumption and production). Additionally, the analyses were mostly obtained using one methodology and demonstrated only by weighting without relationships among factors. To consider the problem of adoption and transition, a systematic method should be developed. Therefore, this study intends to identify, prioritize, and display the relationship between EV adoption barriers from an automotive industry perspective using an analytic network process (ANP) and the decision-making trial and evaluation laboratory (DEMATEL) method. The research results show two contributions: First, the identified and prioritized barriers that automakers encounter in EV transition also explored the interrelationships among these barriers. Second, a model comparison of two multicriteria decision-making approaches was conducted to prioritize and identify the interlinkages among EV uptake barriers.

This paper develops a maintenance policy for a multicomponent system subject to hidden failures. Components of the system are assumed to suffer from hidden failures, which can only be detected at inspection. The objective of the maintenance policy is to determine the inspection intervals for each component such that the long-run cost rate is minimized. Due to the dependence among components, an exact optimal solution is difficult to obtain. Concerned with the intractability of the problem, a heuristic method named “base interval approach” is adopted to reduce the computational complexity. Performance of the base interval approach is analyzed, and the result shows that the proposed policy can approximate the optimal policy within a small factor. Two numerical examples are presented to illustrate the effectiveness of the policy.

A new reliability model considering the damage self-healing phenomenon is developed.The model is practical and realistic for many complex systems.The model can be transformed into different shock or degradation models in different parameter settings. Systems experiencing multiple dependent competing failure processes (MDCFP) have attracted much attention in the recent years. Similar to the biological systems, which have the ability to heal after being wounded; damage self-healing exists in many systems and products due to the intrinsic resistance to abrupt damage. The earlier research assumed the dependence between shock process and random shock but didnt take the damage self-healing process into consideration, which occurs in many engineering systems. In the paper, a new reliability model subject to MDCFP by considering the damage self-healing phenomenon is developed. For each random shock, we propose healing time and healing level concept to describe the self-healing process. The model is practical and realistic for many complex systems such as electrical devices or microelectronic polymeric components. Due to complexity of the model, there is no analytical form of the reliability function. However, we estimate the system reliability efficiently by using simulation method. Furthermore, it is shown that the proposed model is general model that can be transformed into many classical degradation and shock models in different parameter settings.

This paper develops an imperfect inspection policy for systems subject to multiple correlated degradation processes. The degradation processes are characterized by a multivariate Wiener process, and the dependency among the processes is described by a covariance matrix. A failure occurs when any of the degradation level exceeds a specific threshold. As degradation-based failures are usually dormant, inspection is required to detect the failures and prevent potential losses. The inspection is imperfect, in such a way that a failure may not be discovered at an inspection. Optimal inspection interval is obtained by minimizing the long run cost rate. In addition, the properties of the optimal inspection interval are studied and the upper and lower bounds of the optimum value are achieved. An example of fatigue crack development is used to illustrate and evaluate the inspection policy. The results imply that inspection accuracy contributes significantly to reducing the operating cost and more efforts should be made to improve the inspection quality.

This paper proposes a variables two-plan sampling system involving normal and tightened inspections, denoted as TNTVSS-, for controlling process fraction nonconforming with a unilateral specification limit based on one-sided capability indices. The system utilises two single variables sampling plans with different sample sizes and the same critical acceptance value , where and are sample sizes required for tightened inspection and normal inspection, respectively. The tightened inspection plan is used when the quality deteriorates and the normal inspection plan is used when the quality is found to be good. The operating characteristic (OC) function of the proposed sampling system is developed based on the exact sampling distribution. The plan parameters under various settings are determined by solving two non-linear equations simultaneously, which satisfy the required quality levels and allowable risks given by the producer and the consumer. The behaviour of the proposed sampling system in terms of the OC ...

This paper investigates the optimal single replacement policy for products with free-repair warranty (FRW) under a finite planning horizon (FPH) from the consumer’s perspective. Within the planning horizon, the product is replaced once by a new product. During FRW, when the product fails, the failed product is rectified using minimal repair without any cost to the consumer. After FRW, any failure of the product incurs a fixed repair cost to the consumer. However, each failure incurs a fixed downtime cost to the consumer over the planning horizon. Under this maintenance scheme, the replacement of the product is investigated for two separate cases: before FRW and after FRW. Then, two cost models from the consumer’s perspective are derived and the optimal replacement policy is obtained such that the expected total disbursement cost is minimized. Finally, numerical examples are given to illustrate the features of the optimal replacement policy under various warranties and planning horizons.

Manufacturing product exhibits several quality characteristics. Quality inspection becomes a crucial way to verify product conformance to requirements. Under certain inspection procedures, we may identify whether the product quality conforms to specifications or not. If the product quality fails to conform, many possible reasons come include problems from the preceding manufacturing process. Performance of the manufacturing equipment is substantial to preserve the production process. The well- maintained equipment ensures the high-quality product. The roles and advantages of quality inspection and equipment maintenance have been individually well-addressed in literatures. The investigations on these two aspects−inspection and maintenance, suggest realizing their relationships as such a way to preserve better quality assurance. However, the link between them has not been sufficiently investigated and modelled. This paper proposes a general framework of interaction between inspection and maintenance, which provide a comprehensive managerial thinking in equipment maintenance. Two approaches are offered to preserve useful initiation of possible joint optimization model for future research

Acceptance sampling plans provide decision rules for lot acceptance determination based on the required quality levels and allowable risks. In this paper, we develop a variables sampling plan based on the one-sided process capability indices, CPU and CPL, when lot resubmissions are permitted on non-acceptance of the original inspection. The plan parameters are determined by solving two non-linear equations simultaneously and fulfill the two-point condition on the operating characteristic (OC) curve. The OC curve of the proposed plan is derived based on the exact sampling distribution rather than approximation. Moreover, the behavior of the proposed resubmitted sampling plan for various parameters is examined and discussed. For practical purposes, the sample size and critical acceptance value are tabulated for various parameter values. An example is used to demonstrate the implementation of the proposed resubmitted sampling plan.

For a multiple component parallel system, the operation of each component is independent, that is, any failure of component will not affect the normal operation of the system. Due to the inevitable deterioration of the component, it may fail more frequently when its age increases. In order to reduce the number of failures, the component should be replaced at a certain age. When a replacement action of the component is performed, it will incur a replacement cost and a setup cost. Under this situation, grouping replacement for all components is an important policy in order to reduce setup cost. This paper derives a formula of the grouping replacement for a n-component parallel system. Further, an optimal grouping replacement method is offered, and the optimal replacement time of each group is obtained.

To make good profits, pricing is a competitive weapon of service firms. This paper is concerned with pricing strategies for services with substantial facility maintenance costs. To address the problem, a mathematical framework that incorporates service demand and facility deterioration is proposed. The facility and customers constitute a service system driven by Poisson arrivals and exponential service times. The most common log-linear customer demand and Weibull-distributed facility lifetime are also adopted. By examining the linkage between customer demand and facility deterioration in profit model, pricing policies of the service are investigated. Then analytical conditions of customer demand and facility lifetime are derived to achieve a unique optimal pricing policy. Finally, numerical examples are presented to illustrate the effects of parameter variations on the optimal pricing policy.

The partnerships of performance-based contracting (PBC) between government and original equipment manufacturer (OEM) have been well demonstrated in most studies, but very few attempts have been made at such partnerships between a foreign government (FG) and a localized third-party logistics (3PL) supplier while they operated the same system. This article constructs a principal-agent model to support resource allocation, and then uses it to analyze commonly observed risk-aversion contracting between a FG customer (principal) and a localized 3PL logistics supplier (agent) with cooperative game combinations by fixed payment, cost-sharing incentive, as well as a performance incentive conditions. Finally, a real military logistics service application in Taiwan is demonstrated by the assessment model to generate the maximum utilities while under cost-sharing incentive condition by using offset obligation between FG and OEM.

This article formulates a novel fuzzy multilevel multiobjective production planning model for a supply chain under a fuzzy environment. An efficient two-phase interactive solution procedure is developed to obtain a good solution that maximizes the total supply chain profit and the satisfactory degree. The proposed solution procedure, modified from Sakawa et al.’s interactive fuzzy programming approach, can be easily adopted by practitioners. Through a negotiation case study, a well-known network product manufacturing supply chain in Taiwan is presented to demonstrate the effectiveness and aptness of the proposed model and the solution procedure, as compared with Sakawa et al.’s method with only one objective at the manufacturer level. Finally, several important findings and managerial implications are drawn from the results of this study.

For survival and success, pricing is an essential issue for service firms. This article deals with the pricing strategies for services with substantial facility maintenance costs. For this purpose, a mathematical framework that incorporates service demand and facility deterioration is proposed to address the problem. The facility and customers constitute a service system driven by Poisson arrivals and exponential service times. A service demand with increasing price elasticity and a facility lifetime with strictly increasing failure rate are also adopted in modelling. By examining the bidirectional relationship between customer demand and facility deterioration in the profit model, the pricing policies of the service are investigated. Then analytical conditions of customer demand and facility lifetime are derived to achieve a unique optimal pricing policy. The comparative statics properties of the optimal policy are also explored. Finally, numerical examples are presented to illustrate the effects of para...

Systems experiencing multiple dependent competing failure processes (MDCFP) have attracted much attention in the recent years. A system subject to MDCFP with damage self-recovery phenomenon is considered in this paper. Due to the intrinsic resistance to abrupt damage, the damage self-recovery exists in many systems and products. A new reliability model subject to MDCFP by considering the damage self-recovery phenomenon is developed. For each random shock, we propose recovery time and recovery level concept to describe the self-recovery process. The model is practical and realistic for many complex systems such as electrical devices or microelectronic polymeric components. Due to complexity of the model, there is no analytical form of the reliability function. However, we estimate the system reliability efficiently by using simulation method.

This paper investigates the optimal length of lease period and maintenance policy for leased equipment. In order to have steady revenue, the lessor (owner) of equipment may provide a discount to encourage the lessee (user) to sign a contract with a longer lease period. However, as the lease period increases, the maintenance cost also increases due to the deterioration or usage of the equipment. Therefore, there is a need to determine an appropriate length of lease period and a corresponding maintenance policy for the leased equipment from the viewpoint of the lessor such that the expected total profit is maximized. In this paper, the following maintenance scheme is considered. When the leased equipment fails, a minimal repair is conducted to bring the equipment back to an operating condition. Furthermore, when the age of the equipment reaches a specified level (called as a control-limit), an imperfect preventive maintenance (PM) is carried out to avoid possible failures. Under this maintenance scheme, the mathematical model of the expected total profit is developed and the optimal length of lease period and the corresponding optimal maintenance policy are derived. Finally, some numerical examples are given to illustrate the effects of the length of lease period and the maintenance policy on the expected total profit.

This paper proposes two maintenance schemes for reused products. In order to reduce the purchasing cost or conform to the concept of environmental protection, reuse is considered as one of the most efficient strategies. However, the initial quality of reused product is often inferior to the new one and then product failures will occur frequently during usage period. Therefore, two periodical preventive maintenance (PM) policies in this paper are developed to decrease the high failure rate of the second-hand products. When a second-hand product with Weibull life time distribution of known age is intended to be used for a pre-specified period of time, the optimal number of PM actions and the corresponding maintenance degree are derived such that the expected total maintenance cost is minimized. The impact of providing preventive maintenance is illustrated through numerical examples.

This paper investigates the effects of preventive-maintenance cost functions on the optimal preventive-maintenance policy for a leased product with Weibull life-time distribution. During the lease period, any product failures are rectified by minimal repairs and may incur a penalty to the lessor, if the time duration for performing a minimal repair exceeds a pre-specified time limit. To reduce repair costs and possible penalty, preventive-maintenance actions are scheduled in the lease contract. The objective of this paper is to derive the optimal preventive-maintenance schedule and maintenance degrees such that the expected total cost is minimized. Some structural properties of the optimal policy are obtained and an efficient algorithm is provided to search for the optimal policy. For the cases where the preventive maintenance cost is a constant or a linearly increasing function, the effects of the preventive-maintenance cost function on the optimal policy are investigated in detail both theoretically and numerically.

This paper investigates the optimal threshold values of age to perform preventive maintenance (PM) actions for leased equipment within the lease period. In this paper, we use age reduction method to describe the degree of PM and construct the maintenance cost function. For repairable leased equipment, two maintenance models are proposed: (i) maintenance policy of single-phase and (ii) maintenance policy of two-phase. During the lease period, PM actions are carried out when the age of equipment reaches a certain threshold value. Any failure of the leased equipment is rectified by a minimal repair within the lease period. Under these maintenance schemes, the mathematical models of the expected total cost for maintenance policies of single-phase and two-phase are established, and the optimal maintenance policies are derived such that the expected total cost is minimized. Finally, the features of the optimal maintenance policy are illustrated through numerical examples.

Previous studies have proposed an integrated production and inspection model for a deteriorating production system whose process is characterized by an exponential distribution. Since the simultaneous determination of the optimal scheduled inspection times and the optimal production run length is difficult, an approximative production and inspection solution is obtained under the condition that the optimal inspection policy is equally-spaced. That is, obtaining an approximative production run length and number of inspections. This study further investigates this approximative solution and demonstrates that how to utilize it to obtain the real optimal solution more efficiently.

This study proposes a maintenance scheme for leased equipment using failure rate reduction method and derives an optimal preventive maintenance (PM) policy that minimizes expected total cost. Under the proposed maintenance scheme, the lessor (equipment owner) rectifies failures with minimal repairs within the lease period, and the lessor may incur a penalty when repair time exceeds a time limit as specified in the lease contract. To reduce the expected total cost, the lessor may employ PM actions to decrease the number of possible failures. In this study, an efficient algorithm is developed to derive the optimal PM policy and a closed-form solution is obtained for the case where the lifetime distribution of the equipment is Weibull. The expected total cost using the optimal PM policy under the proposed maintenance scheme is then compared with the performance of other policies under various maintenance schemes through numerical examples.

Effective personnel assignment is one of the most crucial tasks performed by the decision makers of a company. This paper proposes a systematic approach with a feedback mechanism in which the interdependences among positions and the differences among the selected employees are considered simultaneously. Unfortunately, the two combined considerations have rarely been discussed in the literature. The purpose of this approach is to obtain the best matching of candidates and positions in order to organize a collaboratively cross-functional team. In a fuzzy environment and, then, in the proposed approach, a bi-objective binary integer programming (BOBIP) model is formulated. Based on the weighted composite scores determined in the third step of the proposed procedure, the BOBIP model is transformed into a fuzzy bi-objective goal programming (FBOGP) model. An elaborately designed heuristic algorithm is developed to determine the appropriate values of several important parameters in the FBOGP model, which is solved using LINDO 8.0. An application example is illustrated, and two additional examples are tested. The results indicate that the proposed approach achieves the acceptable satisfaction level and requires less computation time than the brute force enumerative method.

Vendor selection is an evaluation process that is based on many criteria that uses inaccurate or uncertain data. But while the criteria are often numerous and the relationships between higher-level criteria and lower-level sub-criteria are complex, most conventional decision models cannot help us clarify the interrelationships among the sub-criteria. Our proposed integrated fuzzy multiple criteria decision making (MCDM) method addresses this issue within the context of the vendor selection problem. First, we use triangular fuzzy numbers to express the subjective preferences of evaluators. Second, we use interpretive structural modeling (ISM) to map out the relationships among the sub-criteria. Third, we use the fuzzy analytical hierarchy process (AHP) method to compute the relative weights for each criterion, and we use non-additive fuzzy integral to obtain the fuzzy synthetic performance of each common criterion. Fourth, the best vendor is determined according to the overall aggregating score of each vendor using the fuzzy weights with fuzzy synthetic utilities. Fifth, we use an empirical example to show that our proposed method is preferred to the traditional method, especially when the sub-criteria are interdependent. Finally, our results provide valuable suggestions to vendors on how to improve each sub-criterion so that they can bridge the gap between actual and aspired performance values in the future.

This paper investigates the optimal threshold value of failure rates for leased products with a Weibull lifetime distribution. Within a lease period, any product failure is rectified by minimal repairs and the lessor may incur a penalty when the time required to perform a minimal repair exceeds a reasonable time limit. To reduce product failures, additional preventive maintenance actions are carried out when the failure rate reaches a threshold value. Under this maintenance scheme, a mathematical model of the expected total cost is established. Based on the model, the optimal threshold value and the corresponding maintenance degrees are derived such that the expected total cost is minimized. The structural properties of the optimal policy are investigated and an efficient algorithm is provided to search for the optimal policy. Finally, numerical examples are given to illustrate the features of the optimal policy.

This paper investigates the effects of a free-repair warranty on the periodic replacement policy for a repairable product. Cost models are developed for both a warranted and a non-warranted product, and the corresponding optimal periodic replacement policies are derived such that the long-run expected cost rate is minimized. For a product with an increasing failure rate function, structural properties of these optimal policies are obtained. By comparing these optimal policies, we show that the optimal replacement period for a warranted product should be adjusted toward the end of the warranty period. Finally, examples are given to numerically illustrate the impact of a product warranty on the optimal periodic replacement policy.

Failure mode and effect analysis (FMEA) is a widely used risk assessment tool to identify the potential failure modes of a product or a process. By ranking the priorities for corrective action according to the respective effects of the failures, the chance of the failures can be reduced or eliminated. However, there could be several difficulties during conducting conventional FMEA such as the subjective and qualitative description in natural language, the relative importance among the risk ratings, the difference of risk representation among the same ratings; and the knowledge shared among FMEA team members. Thus, a new risk assessment system based on fuzzy theory is proposed in this paper to deal with these difficulties. Furthermore, an FMEA is conducted for a sewage plant to demonstrate the proposed fuzzy assessment of FMEA.

This paper develops a mathematical model to jointly determine the optimal lot size and product inspection policy for a deteriorating production system, when products are sold with free minimal repair warranty. Due to system deterioration, a last-K product inspection scheme is proposed, under which the last K products in a production lot are inspected and nonconforming products found are reworked. Based on the model, we show that there exist a unique optimal lot size and a corresponding inspection policy such that the expected total cost per unit time is minimized. Since there is no closed-form expression for the optimal lot size, an upper bound and approximate solutions are obtained to facilitate the search process. Furthermore, an algorithm is provided to efficiently search for the optimal policy and the performance of the optimal policy is evaluated through numerical examples.

This paper develops a mathematical model to derive the optimal periodical preventive maintenance (PM) policy for a leased facility with Weibull life-time. Within a lease period, any failures of the facility are rectified by minimal repairs and a penalty may occur to the lessor when the time required to perform a minimal repair exceeds a reasonable time limit. To reduce failures of the facility, additional PM actions are carried out periodically during the lease period. When the life-time distribution of a product is Weibull, the optimal number of PM actions and the corresponding maintenance degrees are derived such that the expected total maintenance cost is minimized. The structural properties of the optimal policy are investigated and an efficient algorithm is provided to search for the optimal policy. Finally, numerical examples are provided to illustrate the features of the proposed model.

This paper deals with the optimal production/maintenance (PM) policy for a deteriorating production system which may shift from the in-control state to the out-of-control state while producing items. The process is assumed to have a general shift distribution. Under the commonly used maintenance policy, equal-interval maintenance, the joint optimizations of the PM policy are derived such that the expected total cost per unit time is minimized. Different conditions for optimality, lower and upper bounds and uniqueness properties on the optimal PM policy are provided. The implications of another commonly used policy, to perform a maintenance action only at the end of the production run, are also discussed. Structural properties for the optimal policy are established so that an efficient solution procedure is obtained. In the exponential case, some extensions of the results obtained previously in the literature are presented. A numerical example is provided to illustrate the solution procedure for the optimal production and maintenance policy.

This paper develops a mathematical model to derive the optimal preventive maintenance warranty (PMW) policy for repairable products with age-dependent maintenance costs. Under a PMW, any product failures are rectified by minimal repair, and additional preventive maintenance actions are carried out within the warranty period. When the costs for preventive maintenance and minimal repair are age-dependent, the optimal number of preventive maintenance actions, corresponding maintenance degrees, and the maintenance schedule for designing a PMW policy are derived here such that the expected total warranty cost is minimized. Under some reasonable conditions, we show that there exists a unique optimal PMW policy in which the product is maintained periodically with the same preventive maintenance degree. Using this property, an efficient algorithm is provided to search for the optimal policy. Some related models developed in the literature are discussed and these models are in fact special cases of the model proposed in this paper. Furthermore, when the life-time distribution of a product is Weibull, a closed-form expression of the optimal policy is obtained. Finally, the impact of providing preventive maintenance is evaluated through numerical examples.

This paper investigates the effects of a renewing free-replacement warranty on the age replacement policy for a nonrepairable product. For both warranted, and nonwarranted products, cost models are developed, and the corresponding optimal replacement ages are derived such that the long-run expected cost rate is minimized. Furthermore, we show that the optimal replacement age for a warranted product is closer to the end of the warranty period than for a nonwarranted product. Finally, numerical examples are given to evaluate the impact of a product warranty on the optimal replacement age.

This study investigates preventive-maintenance warranty policies for repairable products under resource constraints. To reduce product failures, preventive maintenance is widely adopted in practice, especially when the product is complex and/or expensive. However, in practice, there usually exist some resource constraints in performing a preventive maintenance action for deteriorating products. Therefore, products cannot be maintained back to a predetermined condition. In this study, a general warranty cost model for repairable products under resource constraints is established. Based on the model, the properties of optimal preventive-maintenance warranty policies are investigated. Using these properties, algorithms are provided to derive the optimal policies such that the expected total warranty cost is minimized. Finally, when the lifetime distribution of a product is Weibull, a closed-form solution of the optimal policy is obtained.

This study investigates preventive-maintenance warranty (PMW) policies for repairable products with age-dependent maintenance costs. The primary role of warranty is to offer post-sale remedy for consumers when a product fails to fulfill its intended performance during a warranty period. For repairable products, the most commonly used warranty policy is the minimal repair warranty. To reduce product failures, preventive maintenance is widely adopted in practice, especially when the product is complex and/or expensive. For most PMW policies discussed in the literature, there is a basic assumption that the cost of each maintenance action is constant. However, the cost of a maintenance action is varied as the age of repairable products increases in general. Therefore, a general cost model for repairable products with age-dependent maintenance costs is established in this study to derive the optimal PMW policy such that the expected total warranty cost is minimized.

Project priority strategy is the benchmarking of a corporate operation management strategy and in particular is used by a projects-based research and development firm in the complex competence environment of the information and communication technology (ICT) industry. This research takes the variables of external environments and internal resources into account for a firm’s market, technology, and finance assets in order to present a decision process on a project priority strategy. This empirical study also addresses the key factors of the interaction between business on a project development’s supply chain: clients, the examined firm, and suppliers. The findings indicate that a profit-driven project can dominate the firm’s strategic operations and management from the resource-based view and analytic hierarchy process technique perspectives. At the same time, the analysis results contribute significant values to project decision management, which is highly recommended for small-medium enterprises conducting product/project development, project portfolio management, and strategic business management.

This paper investigates preventive-maintenance warranty (PMW) policies for repairable products. When the length of a warranty period is pre-specified, the optimal number of preventive maintenance actions, corresponding maintenance degrees, and the maintenance schedule are jointly determined. We show that there exists a unique optimal policy such that the expected total warranty cost is minimized. Under some reasonable conditions, structural properties of the optimal policy are obtained. Using these properties, an algorithm is provided to efficiently search for the optimal policy. In the case where the failure density is Weibull, a closed form expression of the optimal policy is derived. Finally, the impact of providing preventive maintenance within a warranty period is illustrated through a numerical example.

In this paper we consider a Bayesian theoretic approach to determine an optimal adaptive preventive maintenance policy with minimal repair. By incorporating minimal repair, maintenance and replacement, the mathematical formulas of the expected cost per unit time are obtained. When the failure density is Weibull with uncertain parameters, a Bayesian approach is established to formally express and update the uncertain parameters for determining an optimal adaptive preventive maintenance policy. Furthermore, various special cases of our model are discussed in detail.

This article studies the optimal production run length for a deteriorating production system in which the products are sold with free minimal repair warranty. The deterioration process of the system is characterized by a two-state continuous-time Markov chain. For products sold with free minimal repair warranty, we show that there exists a unique optimal production run length such that the expected total cost per item is minimized. Since there is no closed form expression for the optimal production run length, an approximate solution is derived. In addition, three special cases which provide bounds for searching the optimal production run length are investigated and some sensitivity analysis is carried out to study the effects of the model parameters on the optimal production run length. Finally, a numerical example is given to evaluate the performance of the optimal production run length.

Consider a product that has several quality attributes for inspection where the inspection of some attributes may have carryover effect(s) on subsequent inspections of other attributes. In this case, not all the attributes can be inspected on the same unit and therefore more than one unit may be required to complete one inspection cycle of all the attributes. Furthermore, if the inspection time of each attribute is considered, the number of attributes and their inspection sequence on each inspected unit may affect the time-span of an inspection cycle. In this paper, heuristic procedures are developed to find the inspection sequences of all the attributes that minimize the total number of inspected units and to balance the inspection time of each inspected unit such that the time-span of an inspection cycle is minimized. An integrated circuit card inspection example is given to illustrate the implementation of these procedures.

In this article, a Bayesian approach is developed for determining an optimal age replacement policy with minimal repair. By incorporating minimal repair, planned replacement, and unplanned replacement, the mathematical formulas of the expected cost per unit time are obtained for two cases – the infinite-horizon case and the one-replacement-cycle case. For each case, we show that there exists a unique and finite optimal age for replacement under some reasonable conditions. When the failure density is Weibull with uncertain parameters, a Bayesian approach is established to formally express and update the uncertain parameters for determining an optimal age replacement policy. Further, various special cases are discussed in detail. Finally, a numerical example is given.

This paper investigates imperfect maintenance policies for deteriorating production systems such that the economic manufacturing quantity (EMQ) can be obtained. We consider the case that maintenance action is imperfect and may lead a production system to a worse condition. In this case, two commonly used maintenance strategies are proposed: equally spaced and equally cumulative-hazard. Under both maintenance strategies, optimal maintenance policies can be obtained by any search procedure. Numerical examples are also provided to evaluate the performance of the optimal policies.

This paper investigates the optimal state-dependent replacement policy for semi-Markovian deteriorating systems. It is assumed that the replacement time, replacement cost, operating cost rate and sojourn time distributions are all state-dependent. The optimization criterion is to minimize the expected long-run cost per unit time. Under some sufficient conditions on the cost and time parameters, we show that the optimal policy is of control limit type and has monotonic properties which facilitate the derivation of the optimal policy. Finally, a numerical example is given to illustrate the structure of the optimal policy.

This paper investigates state-age-dependent maintenance policies for multistate deteriorating systems with Erlang sojourn time distributions. Since Erlang distributions are serial combinations of exponential phases, the deteriorating process can be modeled by a multi-phase Markovian model and hence easily analyzed. Based on the Markovian model, the optimal phase-dependent inspection and replacement policy can be obtained by using a policy improvement algorithm. However, since phases are fictitious and can not be identified by inspections, two procedures are developed to construct state-age-dependent policies based on the optimal phase-dependent policy. The properties of the constructed state-age-dependent policies are further investigated and the performance of the policy is evaluated through a numerical example.

In this paper, a phase-type approach is proposed to derive optimal inspection and replacement policies for semi-Markovian deteriorating systems. In this approach, the general sojourn time distributions of a semi-Markovian maintenance model are approximated by acyclic phase-type distributions. Using the approximation, a semi-Markovian maintenance model can be transformed into a Markovian maintenance model such that the analytical tractability of Markov processes can be preserved. Based on the Markovian model, algorithms are provided to derive the optimal state-dependent and state-age-dependent inspection and replacement policies such that the expected long-run cost rate is minimized. Furthermore, procedures are developed to implement the optimal policies on semi-Markovian deteriorating systems. The implementation of the optimal policies are illustrated by numerical examples.

An engine fuel supply subsystem for particular type of aircraft plays an important role in providing, controlling, and distributing the fuel during engine operation. Failure on this subsystem will affect the readiness of the aircraft for operations. Therefore, for system experienced an aging characteristic or wear-out period, determining of the optimal preventive maintenance and optimal preventive replacement interval by considering the total cost of maintenance per unit time is important. In order to support the replacement activity, available number of spare parts required and must be well controlled to avoid either over stock or shortage. In this study, we attempt to determine the preventive maintenance interval and preventive replacement interval and its required inventory spare parts as well. We deliberate the cost structure, failure field data, and the reliability along the designing and managing the maintenance activity. We also examine the implication of the designed maintenance interval on reliability and availability of the system.