Warranty Period Research Articles

A comprehensive study on the important faults in heat pump system during the warranty period

The heat pump market has become mature in many countries. There are millions of heat pumps installed worldwide. So any improvement in the installation, operation, and maintenance of heat pump systems can save a considerable amount of energy and cost, and reduce Green House Emissions to a large extent. The present study suggests a Smart Fault Detection and Diagnosis (SFDD) mechanism as the essential part of the next generation of heat pumps. A SFDD mechanism can minimize the installation and control errors, decrease the performance degradation during operation, avoid unnecessary visual inspections and components replacement, and reduce the maintenance cost and down-time of the system. To develop a SFDD mechanism, the first essential step is to obtain knowledge about the most common and expensive faults experienced by heat pumps. The heat pump manufacturers are one of the best sources to find out the most common and costliest faults occurring in heat pump systems during the first few years of their life. The present paper, as the first part of two, describes the results from a comprehensive study done on the most recent faults which were reported to some of the heat pump manufacturers in Sweden during the warranty period. The most common and the costliest faults in the Air/Air, Air/Water, Brine/Water, and exhaust air heat pumps are presented. Some of the faults such as faulty pressure switches or fans are only related to the heat pump unit, i.e. the thermodynamic cycle which facilitates the heat pumping cycle. Some of the common and expensive faults such as faulty shuttle or shunt valve are related to the faulty components in the heating systems. Generally, the results show that faults in Control and Electronics are almost the most common and costliest faults in all types of heat pumps. Faults in Control and Electronics include any fault related to control unit, electrical faults (such as short circuit, etc.), Printed Circuit Board (PCB), display, soft starter, overcurrent and motor protection relay, etc.

Discussion on the Cost Management and Control of Construction Project

The cost control of the engineering construction project is a complex dynamic system, which is throughout the whole project process, starting from the bid to the end of the project warranty period and every link needs to implement scientific and strict cost control. It is very important to study and work at the cost control of the engineering construction project and to improve the service efficiency of the construction funds. This paper expounds the connotation and significance of the cost control of the engineering construction project, focusing on the analysis of the construction of the project before construction, construction process and construction after the main work links in each stage of cost control methods and measures, which provides reference for the engineering construction enterprise to cost control and improve the level of project management.

Optimal maintenance level for second‐hand product with periodic inspection schedule

This paper formulates a periodic inspection/upgrade model under free non‐renewable warranty policy with a fixed length of warranty period for the second‐hand product and derives an optimal number of inspections required and an optimal improvement level to minimize the expected total warranty cost from the perspective of the dealer during the warranty period. At each inspection, the product is taken an upgrade action in order to reduce its failure rate, which is characterized by an improvement level. It is true in general that the higher improvement level and more frequent inspections increase the warranty cost but lower the chance of product failures. In this paper, we propose an optimal strategy with respect to the inspection/upgrade action for the dealer to lower the total warranty cost. Firstly, we define an inspection/upgrade action, which reduces the product's failure rate proportionally to the improvement level at each inspection and then evaluate the expected total warranty cost. Secondly, the optimal solutions for the decision variables and its uniqueness are discussed in general. Numerical results are presented when the failure distribution follows a Weibull distribution under the proposed model. Copyright © 2014 John Wiley & Sons, Ltd.

Optimizing upgrade level and preventive maintenance policy for second-hand products sold with warranty

With the steady growth of second-hand products’ market, offering warranty for second-hand products is becoming popular for dealers in order to meet customers’ requirement. During that process, upgrade actions and maintenance policies are of great importance. In this article, an optimization model for second-hand items sold with non-renewing free repair warranty is proposed from the view of dealers, in which a second-hand product is subjected to upgrade action at the end of its past life and during the warranty period, preventive maintenance actions are carried out when the age of the product reaches a pre-specified threshold value. Optimal upgrade level and preventive maintenance policy are jointly derived so that the dealer’s expected profit can be maximized. The structural properties of the optimal policies are investigated. Finally, a numerical example and sensitivity analysis are provided to demonstrate the proposed approach.

Warranty return policies for products with unknown claim causes and their optimisation

In practical warranty services management, faults may not always be found in claimed items by warranty service agents, which is the well-known no-fault found phenomenon (for example, caused by a loose connection between parts, or simply human error). This phenomenon can contribute more than 40% of reported service faults in electronic products and it can be due to faults of manufacturers or product users. Little research, however, considers this phenomenon in warranty management since faults are normally assumed to be found in the claimed items. On the basis of different levels of testing, this paper proposes three warranty return policies, which decide whether new items should be sent to warranty claimants or not. It then derives and compares the expected costs of the policies, and obtains the optimal warranty periods under supply chain environments. The paper illustrates the results with artificially generated data.

Joint optimisation of price, warranty and recovery planning in remanufacturing of used products under linear and non-linear demand, return and cost functions

We investigate joint optimisation of remanufacturing, pricing and warranty decision-making for end-of-life products. A novel mathematical–statistical model is proposed where decisions involve pricing of returned used products (cores), degree of their remanufacturing, selling price and the warranty period for the final remanufactured products. The virtual age reliability improvement approach is chosen to model the upgrading of the cores to higher quality levels. We consider price- and warranty-dependent demand, price- and age-dependent return, and age-dependent remanufacturing cost in the model development. Both linear and non-linear forms of these functions are investigated. First, under some restrictive conditions of upgrade level and age distribution of received cores, special cases of the problem, which can be solved using a recently developed non-linear optimisation solver, are presented. We also implement a particle swarm optimisation algorithm for the solution of the original problem when all the restrictive assumptions are dropped. Finally, numerical experiments and sensitivity analysis are presented to address different aspects of the model and the solution approaches.

Three-level warranty service contract among manufacturer, agent and customer: A game-theoretical approach

A warranty is a service contract between a manufacturer and a customer which plays a vital role in many businesses and legal transactions. In this paper, various three-level service contracts will be presented among the following three participants; a manufacturer, an agent, and a customer. In order to obtain a better result, the interaction between the aforementioned participants will be modeled using the game theory approach. Under non-cooperative and semi-cooperative games, the optimal sale price, warranty period and warranty price for the manufacturer and the optimal maintenance cost or repair cost for the agent are obtained by maximizing their profits. The satisfaction of the customer is also maximized by being able to choose one of the suggested options from the manufacturer and the agent, based on the risk parameter. Several numerical examples and managerial insights are presented and used to illustrate the models presented in this paper.

When to stop testing multi upgradations of software based on cost criteria

Software testing is an important phase of the software development life cycle to achieve highly reliable software. Due to the time and resource limitation during the testing phase, firms do not attempt to deliver a complete and perfect product in one development cycle. They plan multi upgradations of software by adding new functionalities. Many models have been developed in the past which discuss about when to stop testing and when to release the software to the users. But they have been limited to the study of single version only. In the present framework, we describe a unified approach to address an important issue of when to stop testing the multi-upgradation of software, which is a complex process. The total debugging cost for each upgradation includes the cost of debugging in the warranty period along with the testing cost. It is assumed that the software is supported till the warranty period is over. In the proposed cost model for each upgradation, we consider that some of the remaining faults of previous release are reported and removed partly during the testing period and partly during the warranty period of new upgradation. An algorithm for finding the optimal release time for each version is developed. We estimate the parameters of the model using Statistical Package for Social Sciences on the real data set, and obtain optimum stopping time for each version of the software using Maple software.

가정용(家庭用) 가스 보일러의 보증기간내(保證期間內) 수리율(修理率)에 관(關)한 실증적(實證的) 연구(硏究)(I)

As Crosby notes, the most companies spend 15 to 20% of their sales dollars on quality costs. Generally the most effective way to manage quality costs is to avoid having defects in the first place. In this paper we have studied about the repair(service) problem of domestic gas boiler within warranty period. We develop a system, which man could find the cause of the problem at an early stage and could devise a countermove to the problem under supposing that the service(repair) rate follows exponential distribution and the product is manufactured lot-for-lot continually. Using the developed early sensing system. it is expected to improve the reliability of the product, to save expenses of company and to improve customer's satisfaction. And the system will be expended to incorporate information technology, which can detect the repair rate automatically.

Release time problem with multiple constraints

Quality of software system generally depends on how much time testing takes and what testing methodologies are used. One attribute of quality is reliability which can be increased by removing more faults from the software and this can be done by spending more time on testing. However, spending more time on testing will increase cost of the software development process. On the other hand, if testing time is too short, testing cost of software may be reduced but it will increase the chance of getting unreliable software and customers may not take higher risk of buying unreliable software. Highly competitive market conditions have forced developers to offer highly reliable products to the users. Software warranty is one such indicator used by the users to judge its reliability with the perception that a longer warranty period indicates higher reliability. Software warranty is a tool which provides assurance about the quality. Warranty cost may be reduced by providing more reliable product. Therefore software reliability, testing, warranty period and cost needs to be considered jointly. In this paper, we propose a new method to estimate the optimal software release time of a software with warranty under imperfect debugging environment by using Multi Attribute Utility Theory. More precisely, three significant attributes, namely Reliability, Cost and Detection rate indicator are used to determine the optimal release time of software under warranty. The proposed new decision model based on multi-attribute utility analysis is tested on the real world data set.

Modelling the repair warranty of an industrial asset using a non-homogeneous Poisson process and a general renewal process

This paper considers selecting the warranty period after the completion of a series of successive repairs on a product. Two stochastic failure models are used: the general renewal process (GRP) model and the non-homogeneous Poisson process (NHPP) model. Both use a Weibull distribution for the life time of the product, allowing the possibility to renewal (GRP) or not (NHPP) when successive repairs are performed. The NHPP is applied to estimate the warranty period after simple repairs (minimal), while GRP is used when repairs are complex (overhauls). The main novelty of this work is the process followed to estimate the warranty period, which can be defined according to the risk that a company is willing to assume in the market. Our procedure provides a useful tool for a maintenance company or for a manufacturer's after-sales division.

Optimal price and testing time of a software under warranty and two types of imperfect debugging

When a product is purchased and used by a customer then it might be possible that a difference between the product performance and customer expectation crops in. A warranty is simply a formal promise by a vendor that the product is defect free, meaning that it will do what it promises to do and that if it fails to do so, then how the vendor will go about rectifying defects. Warranties are also an effective means of promoting a product in the market when the company or product is not well known. Or in other words warranty serves as a source for spread of an innovation in the market. But servicing a warranty engages additional costs to the manufacturer and this has an effect on the profit levels. Warranty cost may be reduced by providing higher reliable product. The conflict existing in the context of software reliability, warranty period and selling price need to be considered jointly. In this paper, we formulate an optimization problem that determines the optimal testing time and price under two types of imperfect debugging of software product with warrant. The factors like fixed cost of testing and debugging during testing phase and warranty period, cost of testing up to the release time are considered in order to maximize profit. Results are illustrated in the numerical example.

Warranty period of normal stress myocardial perfusion imaging in diabetic patients: A propensity score analysis

BackgroundWe evaluated the relationship between diabetes and temporal characteristics of cardiac risk at long-term follow-up in a propensity score-matched cohort of diabetic and non-diabetic patients with normal stress myocardial perfusion single-photon emission computed tomography (MPS). Methods and ResultsWe studied 828 consecutive patients with suspected or known coronary artery disease and normal perfusion at stress MPS. To account for differences in baseline characteristics between diabetics and non-diabetics, we created a propensity score-matched cohort considering clinical variables and stress type. After matching, clinical characteristics were comparable in 260 diabetic and 260 non-diabetic patients. All patients were followed for at least 1 year (median 53 months). End-point events were cardiac death or nonfatal myocardial infarction. At Cox analysis, diabetes (hazard ratio 3.9, P < .01) and post-stress left ventricular ejection fraction (LVEF) ≤45% (hazard ratio 4.1, P < .01) were independent predictors of events. At parametric analysis, non-diabetic patients with post-stress LVEF >45% remained at low risk for the entire length of follow-up, while the highest probability of events and the major risk acceleration was observed in patients with diabetes and post-stress LVEF ≤45%. ConclusionsAfter a normal stress MPS, diabetic patients are at higher risk for cardiac events than non-diabetic subjects also after balancing clinical characteristics and stress type by propensity score analysis. The warranty period of a normal stress MPS varies according to diabetic status and post-stress LVEF.

Fatigue Life Modeling for Elastomeric Materials: a Review

In recent years, influence of elastomer and rubber has increased significantly in engineering applications. Many factors provide long term durability and mechanical fatigue including nucleation and growth of cracks in the rubber is the first attention. Fatigue life prediction on the rubber parts was essential in relation to the extension of warranty period of the automotive components. A design of rubber parts versus fatigue failure is one of the serious topics to check the failures during the operation. To describe the subject efficiently and commercially, engineers require to model and design for mechanical fatigue in the manufacture process. This study presents a review of fatigue life failure criteria, fatigue damage behavior for elastomers and results of the attempts on predicting the experimental results of fatigue life rubber components

The comparativestudyon the influenceof warranty period to thepractical age-replacementunder two situations

The paper focus on analyzing the impact of warranty periods on the optimal age-replacement from the consumers'perspectives.First we construct themathematical formulations for age -replacement model.After optimizing we find there exists a unique optimal replacement age based the long-run expected cost rate is minimized.Further,a concise numerical example is demonstrated, and the sensitivity analysis of the warranty period to practicalreplacement age is carried out as well.Afterwards, the influnce of warranty periods on the optimal age-replacement under two situations thatpreventive replacement is within and beyond the warranty periods are comparedanalytically. Keywords: Warranty period;Practicalreplacement age;Preventive replacement age;Long-run expected cost rate.

Optimal Overhaul-Replacement Policies for a Repairable Machine Sold with Warranty

This research deals with an overhaul-replacement policy for a repairable machine sold with a free replacement warranty (FRW), which will be used for a finite horizon T and evaluated at fixed interval s. At each evaluation point, the buyer considers three alternative decisions, i.e. (1) keep the machine, (2) overhaul it, or (3) replace it with a new identical one. If the machine fails during the warranty period, this is rectified at no cost to the buyer. Any failure occurring before and after the expiry of the warranty is restored by minimal repair. An overhaul-replacement policy was formulated using a dynamic programming approach. The results show that overhaul rejuvenation may extend the machine life cycle and delay the replacement decision. In contrast, the warranty stimulates early machine replacement and in so doing increases the replacement frequency for a certain range of replacement costs. This implies that in order to minimize the total ownership costs over T, the buyer needs to consider the minimal repair cost reduction due to the rejuvenation effect of an overhaul as well as the warranty benefit due to replacement. Numerical examples are presented for both illustrating the optimal policy and describing the behavior of the optimal solution.

Multi-manufacturer single-retailer supply chain model under price- and warranty period-dependent demand

In reality, many manufacturers produce different brands of the same item to sell through a common retailer. This paper deals with such a supply chain scenario in which the demand at the downstream player (retailer) is dependent on price as well as the length of the warranty period offered by the upstream player (manufacturer). A game-theoretic framework is applied to obtain the equilibrium solution for each entity. Our analysis reveals that the non-cooperative game leads to lower channel profit whereas, the retailer-Stackelberg and manufacturer-Stackelberg games can lead to higher channel profit. A numerical example is taken to compare the outcome of the supply chain model under different scenarios and to examine the impact of model-parameters on optimal solutions.

Profit maximization by virtue of price & warranty length optimization

Warranties serve as persuasive marketing tools: (i) promotional and (ii) protectoral. As a promotional tool, warranties serve to promote the reliability and quality of a product with longer and better warranty terms implying a more reliable product. As a protectoral tool, warranties provide assurance to consumers against defective products that fail to perform satisfactorily over the warranty period. This assurance reduces the risks associated with purchase of the product but introduces some impedimentation in profit management for the manufacturer. Using a two dimensional innovation diffusion model to demonstrate product sales cycle, this study presents a methodical approach to obtain optimal price and warranty length for a product. The model examines significance of these decision variables and estimates the overall maximum profit for the manufacturer. Exponential distribution has been used to represent the life time distribution of a product and the model has been validated using real life data set.

Обобщенная оценка свойств лакокрасочного покрытия

In the article the results of a question of preservation of protective and decorative properties of nitrocellulose lacquer coating applied to a substrate of synthetic veneer. The author´s task was to determine the quality of the coatings, which were kept in storage conditions, and operated in a residential area within the warranty period of service of furniture products. The quality of coatings decreases with time due to changes in color, dirt collection, light changes, local swelling (decorative features change), crac-king, delamination, fracture.

Optimizing the warranty period by cuckoo meta-heuristic algorithm in heterogeneous customers’ population

Warranty is now an integral part of each product. Since its length is directly related to the cost of production, it should be set in such a way that it would maximize revenue generation and customers’ satisfaction. Furthermore, based on the behavior of customers, it is assumed that increasing the warranty period to earn the trust of more customers leads to more sales until the market is saturated. We should bear in mind that different groups of consumers have different consumption behaviors and that performance of the product has a direct impact on the failure rate over the life of the product. Therefore, the optimum duration for every group is different. In fact, we cannot present different warranty periods for various customer groups. In conclusion, using cuckoo meta-heuristic optimization algorithm, we try to find a common period for the entire population. Results with high convergence offer a term length that will maximize the aforementioned goals simultaneously. The study was tested using real data from Appliance Company. The results indicate a significant increase in sales when the optimization approach was applied; it provides a longer warranty through increased revenue from selling, not only reducing profit margins but also increasing it.