Stefanka Chukova

Maintenance models in warranty: A literature review

Along with increasing the warranty period for complex systems, reducing the warranty servicing costs has become an issue of great importance to the manufacturers. One possible way to reduce the expected warranty servicing cost is by making sound decision on the product warranty and maintenance strategies. Therefore, warranties (basic warranty and extended warranty) and maintenance (corrective and preventive) are strongly interlinked and of great interest to both manufacturers and customers. This paper is the first identifiable academic literature review to deal with warranty and maintenance. It provides a classification scheme for the articles that link warranty and maintenance published between 2001 and 2011 covering 44 journals and proposes a taxonomy scheme to classify these articles. Nine hundred articles were identified for their relevance to warranty and were carefully reviewed. One-hundred and twenty-two articles were subsequently selected for their relevance to maintenance and included in the classification.

Two-dimensional warranty repair strategy based on minimal and complete repairs

For repairable products, the warrantor has options in choosing the degree of repair applied to an item that has failed within the warranty period. We focus on a particular warranty repair strategy, related to the degree of the warranty repair, for non-renewing, two-dimensional, free of charge to the consumer warranty policy. We consider a rectangular warranty region and divide it into three disjoint subregions, so that each of these subregions has a preassigned degree of repair for a faulty item. Our main goal is to determine the subregions, so that the associated expected warranty servicing cost per item sold is minimised. A comparison between our strategy and previously studied, more restrictive, ones is provided.

On optimal upgrade level for used products under given cost structures

Abstract In spite of the growing share of the second-hand market, often customers of used products encounter the following three problems: (a) they are uncertain regarding the durability and performance of these products due to lack of information on the item’s past usage and maintenance history, (b) they are uncertain about the accurate pricing of warranties and the post-warranty repair costs, and (c) sometimes, right after the sale, used items may have high failure rate and could be harmful to their new owner. Due to these problems, the dealers are currently carrying out actions such as overhaul and upgrade of the used products before their release. Reliability improvement, which is closely related to the concept of warranty, for used products is a relatively new concept and has received very limited attention. This paper also develops a stochastic model which results in the derivation of the optimal expected upgrade level under given structures of the profit and failure rate functions. We provide a numerical study to illustrate our results.

Two-Dimensional Warranty Cost Analysis for Second-Hand Products

In spite of the recent steady increase of the volume of the second-hand markets, often customers remain in doubt regarding the quality and durability of the second-hand products. Aiming to reduce and share this uncertainty, dealers offer warranty on their products. Offering warranty for second-hand products is a relatively new marketing strategy employed by dealers of used electronic equipment, furniture, automobiles, etc. Usually, for used products, the dealers expected warranty cost is a function of product reliability, past age and usage, servicing strategy and conditions and terms of the warranty policy/contract. Sometimes the offered policy is limited by two parameters, typically the product age and usage after the sale. This type of policies is referred to as two-dimensional warranty policies. In this article, we develop statistical models for estimating the dealers expected warranty cost for second-hand products sold with two-dimensional free repair/replacement warranty.

On the investment in a reliability improvement program for warranted second-hand items

A reliability improvement program (such as an upgrade action) can be seen as an investment by a dealer to restore a second-hand product to a better operational state. Due to the nature of the actions performed, the items reliability at the end of this program is usually uncertain. This article develops a stochastic cost–benefit model for investment made in reliability improvement programs for second-hand items sold with failure-free warranty. Depending on the products lifetime modeling approach, two modifications of the model are considered and are solved for the optimal improvement level. A real case application of the model is presented to validate the proposed approach.

Warranty cost analysis: quasi‐renewal inter‐repair times

Purpose – To provide a brief introduction to warranty analysis and a classification of general repairs. To introduce the notion of accelerated probability distribution and use it to model imperfect warranty repairs.Design/methodology/approach – The notion of accelerated probability distribution is discussed and its similarity with quasi‐renewal and geometric processes is observed. An approach to modeling imperfect warranty repairs based on the accelerated probability distributions is presented, and the corresponding expected warranty cost over the warranty period under non‐renewing free replacement warranty policy is evaluated.Findings – It is observed that quasi‐renewal and the geometric processes are equivalent. Using data from an existing warranty database it is shown that the inter‐repair times form a quasi‐renewal process. The corresponding expected warranty cost over the warranty period under a non‐renewing free replacement warranty policy is evaluated.Research limitations/implications – This approa...

WARRANTY COST ANALYSIS: RENEWING WARRANTY WITH NON-ZERO REPAIR TIME

The main focus of this study is on the modeling of the warranty claims and evaluating the warranty expenses. The cost of each warranty claim depends on the repair time associated with the claim. Alternating renewal process is used to model the operating and repair times. The warranty costs over the warranty period under renewing free replacement policy are evaluated. Also, the expected warranty expenses over the life cycle of the product are studied. Numerical examples illustrate the ideas.

Probability distributions in periodic random environment and their applications

Periodic random environments and mechanisms of their effect on imbedded random variables are discussed. The variables under consideration represent either waiting time until some event occurs or the number of events within a given time interval. Their probability distributions have periodic residual lifetime functions and periodic failure rates. The form of the corresponding cumulative distribution functions is derived. Equivalent representations of these random variables as functions of other, suitably chosen independent random variables are established. Other probability properties such as almost lack of memory, invariance with respect to relevation transform, and preservation of service time distribution on nonreliable servers are additional characterizing features of this class of probability distributions. Nonstationary Poisson processes with periodic failure rates appear to be the closest extension of the homogeneous Poisson process to model the number of events imbedded into random environment of p...

Burn-in and imperfect preventive maintenance strategies for warranted products

Manufacturers are currently carrying out two effective strategies to reduce the warranty servicing cost of products with bathtub shaped failure rates. The first strategy is the burn-in procedure when products are operated for a reasonably short period of time prior to usage. This strategy can be effective when the initial failure rate is strictly decreasing (infant mortality). The second strategy is preventive maintenance actions at discrete time instances over the warranty period which can effectively reduce the age of the item when the failure rate is strictly increasing (wear-out). In this paper, the optimal burn-in time and imperfect preventive maintenance strategies for a warranted product with the bathtub-shaped failure rate are investigated. We provide a numerical study to illustrate our results.

Optimal two-dimensional warranty repair strategy

For repairable products, the warrantor has options in choosing the type of repair performed to an item that fails within the warranty period. The focus is on a particular warranty repair strategy, related to the degree of the warranty repair, under a non-renewing two-dimensional warranty policy that is free of charge to the consumer. A rectangular warranty region, as in the automotive industry, is considered and partitioned into disjoint subregions. Each of these subregions has a preassigned degree of repair for a faulty item. First, for a partition of size n, an expression is derived for the associated expected warranty servicing cost per item sold. Second, using an example, for a given discretization of the warranty period, the way in which the number of subregions and their shape can be determined, so that the expected warranty servicing cost per item sold is minimum, is demonstrated.