Warranty and Sustainable Improvement of Used Products through Remanufacturing

Currently, a large number of used/second-hand products are being sold with remanufacturing. Remanufacturing is a process of bringing used products to a better functional state and can be applied as a way for (1) controlling the deterioration process, (2) reducing the likelihood of a failure over the warranty period and (3) making the used item effectively younger. Remanufacturing is relatively a new concept and has received very limited attention. In this paper, we develop an important sustainable improvement approach for used items sold with failure free warranty to determine the optimal improvement level. Our model makes a useful contribution to the reliability growth literature, as it captures the uncertainty and suggests improvement in the remanufacturing process. By using this model, the dealers can decide whether and how much to invest in remanufacturing projects

Optimal Overhaul-Replacement Policies for Repairable Machine Sold with Warranty

This research deals with an overhaul-replacement policy for a repairable machine sold with Free Replacement Warranty (FRW). The machine will be used for a finite horizon, T (T <ï‚¥), and evaluated at a fixed interval, s (s< T). At each evaluation point, the buyer considers three alternative decisions i.e. Keep the machine, Overhaul it, or Replace it with a new identical one. An overhaul can reduce the machine age virtually, but not to a point that the machine is as good as new. If the machine fails during the warranty period, it 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 is formulated for such machines by using dynamic programming approach to obtain the buyer's optimal policy. The results show that a significant rejuvenation effect due to overhaul may extend the length of machine life cycle and delay the replacement decision. In contrast, the warranty stimulates early machine replacement and by then increases the replacement frequencies for a certain range of replacement cost. This demonstrates that to minimize the total ownership cost over T the buyer needs to consider the minimal repair cost reduction due to rejuvenation effect of 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

Optimal replacement and overhaul decisions with imperfect maintenance and warranty contracts

In this article, we develop a model to help a maintenance decision making situation of a given equipment. We propose a novel model to determine optimal life-cycle duration and intervals between overhauls by minimizing global maintenance costs. We consider a situation where the costumer, which owns the equipment, may negotiate a better warranty contract by offering an improved preventive maintenance program for the equipment. The equipment receives three kind of actions: repairs, overhauls, and replacement. An overhaul represents an imperfect maintenance action, that is, the failure rate is improved but not a point that the equipment is as good as new. Corrective maintenance actions are minimal, in the sense that the failure rate after each repair is the same as before the failure. The proposed strategy surpasses others seen in the literature since it considers at the same time the warranty negotiation situation and the optimal life-cycle duration under imperfect preventive actions. We also propose a simplified approach that facilitates the task of implementing the method in standard solvers

Determinación del tiempo optimo de overhaul de cargadores subterráneos lh202, aplicando modelos de vida económica de sistemas reparables y overhaul imperfecto

Un problema que recibe cada vez más atención en la industria es el costo de mantener flotas de sistemas reparables, a medida que una flota envejece la atención se centra en identificar los principales problemas generadores de costos e implementar cambios para reducir el costo, estos pueden incluir cambios en el diseño, implementación de estrategias de mantenimiento, políticas de reparación y otros. El overhaul se presenta como una estrategia de mantenimiento que mejora el estado de un equipo, afectando significativamente los costos operativos, la confiabilidad, el sustento y la efectividad de toda la flota. El presente trabajo tiene como objetivo general determinar el tiempo óptimo de overhaul aplicando los modelos de vida económica de sistemas reparables y overhaul imperfecto para determinar con aproximación el tiempo óptimo de overhaul de los cargadores subterráneos LH202. Así mismo se estimará la intensidad de fallas, el numero esperado de fallas y MTBF (Tiempo medio entra fallas) aplicando los modelos de Crow Amsaa y Loglineal, determinando así el estado en el tiempo de los equipos LH202 (SC-19, SC-20, SC-21). Aplicando los modelos de Crow Amsaa y Log lineal se determinó que los equipos LH202 pasan por un proceso deterioro, presentándose un incremento acelerado de las fallas en el tiempo. Aplicando los modelos de vida economica de sistemas reparables y overhaul imperfecto se obtuvo el tiempo óptimo de overhaul de los equipos LH202. Modelo de vida economica de sistemas reparables: SC-19 (17945.53 hrs), SC-20 (17307.18 hrs) y SC-21 (17364.83 hrs). Obteniéndose un promedio de 17539.18 hrs. Modelo de overhaul imperfecto: SC-19 (18722.93hrs), SC-20 (18316.25hrs) y SC-21 (18109.73hrs). Obteniéndose un promedio de 18382.97 hrs. Se concluye que los equipos LH202 pasan por un proceso de envejecimiento debiendo considerar al overhaul como estrategia para mejorar su estado, el mismo debe ser ejecutado en un intervalo de tiempo de 17539.18 hrs hasta las 18382.97 hrs

A unified methodology of maintenance management for repairable systems based on optimal stopping theory

This dissertation focuses on the study of maintenance management for repairable systems based on optimal stopping theory. From reliability engineering’s point of view, all systems are subject to deterioration with age and usage. System deterioration can take various forms, including wear, fatigue, fracture, cracking, breaking, corrosion, erosion and instability, any of which may ultimately cause the system to fail to perform its required function. Consequently, controlling system deterioration through maintenance and thus controlling the risk of system failure becomes beneficial or even necessary. Decision makers constantly face two fundamental problems with respect to system maintenance. One is whether or when preventive maintenance should be performed in order to avoid costly failures. The other problem is how to make the choice among different maintenance actions in response to a system failure. The whole purpose of maintenance management is to keep the system in good working condition at a reasonably low cost, thus the tradeoff between cost and condition plays a central role in the study of maintenance management, which demands rigorous optimization. The agenda of this research is to develop a unified methodology for modeling and optimization of maintenance systems. A general modeling framework with six classifying criteria is to be developed to formulate and analyze a wide range of maintenance systems which include many existing models in the literature. A unified optimization procedure is developed based on optimal stopping, semi-martingale, and lambda-maximization techniques to solve these models contained in the framework. A comprehensive model is proposed and solved in this general framework using the developed procedure which incorporates many other models as special cases. Policy comparison and policy optimality are studied to offer further insights. Along the theoretical development, numerical examples are provided to illustrate the applicability of the methodology. The main contribution of this research is that the unified modeling framework and systematic optimization procedure structurize the pool of models and policies, weed out non-optimal policies, and establish a theoretical foundation for further development

A maintenance model for the supply-buffer-demand production system

Master'sMASTER OF ENGINEERIN

Post-Sale Cost Modeling and Optimization Linking Warranty and Preventive Maintenance

Ph.DDOCTOR OF PHILOSOPH

Análise e avaliação de períodos de inspeção em sistemas de natureza tecnológica

Esta tese enquadra-se no domínio da fiabilidade e manutenção de sistemas e centra-se na análise e avaliação de períodos de inspeção em sistemas de natureza tecnológica. O projeto desenvolve um modelo analítico que permite determinar o período ótimo de manutenção e o número ótimo de manutenções preventivas até à substituição do sistema. O modelo tem como base uma política de manutenção preventiva periódica e como objetivo a minimização do custo total de manutenção. Na construção do modelo não são assumidos pressupostos que simplifiquem as expressões analíticas consideradas, não restringindo assim o âmbito da sua aplicação. Além disso, a incerteza de natureza estocástica relacionada com os processos do comportamento (falha, reparação, inspeção, etc.) é modelada por distribuições de probabilidade e a incerteza que se prende com a falta de informação quantitativa, com a escassez de dados, com a falta de conhecimento preciso de alguns parâmetros do modelo é modelada recorrendo à Teoria dos Conjuntos Difusos, o que introduz um acréscimo de realismo ao modelo. O modelo é aplicado a um sistema de controlo de potência ativo de um aerogerador, ilustrando a sua adaptabilidade a sistemas tecnológicos reais e destacando as suas potencialidades e limitações.This thesis is part of the field of systems reliability and maintenance and focuses on the analysis and evaluation of inspection periods of technological nature systems. The project develops an analytical model for determining the optimum period of maintenance and the optimal number of preventive maintenances until the system replacement. The model is based on a periodic preventive maintenance policy and aims to minimize the total cost of maintenance. In the model construction phase no assumptions are made to simplify the analytical expressions, thus not constraint its applicability to real systems. Moreover, the uncertainty of stochastic processes related to behavior (failure, repair, inspection, etc..) is modeled by probability distributions and the uncertainty due to lack of quantitative information, scarcity of data and lack of precise knowledge out some parameters of the model is modeled using the Fuzzy Set Theory, which introduces an increase of realism to the model. The model is applied to an active power control system of a wind turbine, illustrating its adaptability to real technological systems and highlighting its strengths and weaknesses