• Journal of Applied Reliability
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• v.17 no.2
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• pp.83-91
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• 2017

Purpose: The purpose of this study is to develop a quality assurance model and to determine appropriate warranty period for a guided missile using its field data. Methods: 10 years of actual firing data is collected from the defense industry company and military. Parametric maximum likelihood estimation for a reliability function is determined with the data. Results: The reliability function estimates average lifetime of the missile. That function shows a user requirement, 80% reliability (lifetime) is come up when 8 years have passed, which is longer than the estimates in the missile's development phase. Conclusion: Quality assurance warranty for a guided missile must be established with actual test data. It is necessary to update and modify the reliability prediction and the warranty period with actual field test data.

• Journal of the Korean Data and Information Science Society
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• v.24 no.4
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• pp.773-781
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• 2013

Recently, an extended warranty of the system following the expiration of the basic warranty is becoming increasingly popular to the user. In this respect, we suggest a preventive maintenance model following the expiration of extended warranty with minimal repair warranty from the user's point of view in this paper. Under basic warranty and extended warranty, the failed system is minimally repaired by the manufacturer at no cost to the user. For the preventive maintenance model, we derive the expressions for the expected cycle length, the expected total cost and the expected cost rate per unit time. Also, we determine the optimal preventive maintenance period and the optimal preventive maintenance number by minimizing the expected cost rate per unit time. Finally, the numerical examples are presented to illustrate the purpose when the failure time of the system has a Weibull distribution.

• Communications for Statistical Applications and Methods
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• v.17 no.6
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• pp.865-877
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• 2010

This paper considers the periodic preventive maintenance model for a repairable system following warranty expiration. We consider three types of warranty policies: free repair warranty, pro-rata repair warranty, and combination repair warranty. Under these preventive maintenance models, we derive the expressions for the expected cycle length, the total expected cost, and the expected cost rate per unit time. In addition, we explain the optimal preventive maintenance period and the optimal preventive maintenance number by minimizing the expected cost rate per unit time. Finally, the optimal periodic preventive maintenance policy is given for a Weibull distribution case.

• Proceedings of the Korean Reliability Society Conference
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• 2004.04a
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• pp.97-106
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• 2004

Contractual agreement (relating to product performance). Established on sale of product. Requires the manufacturer to either rectify failures occurring over the warranty period or compensate through refunding a fraction of the sale price.(omitted)

• Journal of Korean Society for Quality Management
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• v.24 no.1
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• pp.1-9
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• 1996

Ritchken(1985) analyzes free replacement and pro-rata warranty policies for products receiving renewable warranies. He shows that for constant failure rates pro-rata warranty policies are more attractive to risk-averse manufacturers than shorter term free replacement policies that result in the same average warranty cost. This paper considers the case when product lifetimes distributions are of phase-type. When this is so, Ritchken's performance measures can be simplified considerably. It is found, that irrespective of the pattern of failure rates, pro-rata warranty policies are preferable to free replacement policies. But the warranty period of the equivalent free replacement policy decreases and then increases, as product reliability(the average time between failures) increases.

• Journal of Korean Society for Quality Management
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• v.22 no.1
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• pp.113-121
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• 1994

Present worth of warranty cost for an irrepairable item is derived under free-replacement, prorata and hybrid warranty policies, respectively. In this paper, it is assumed that the lifetime distribution is a Gamma, and warranty period is not renewed but maintained as promised at the selling time regardless of replacements due to warranty contract. A numerical example on the relationship between present worth of warranty cost and mean time to failure is included.

• International Journal of Reliability and Applications
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• v.15 no.1
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• pp.51-64
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• 2014

This paper develops a warranty cost model for complex systems with imperfect repair within a warranty period by addressing a practical case that the first inter-failure interval is longer than any other inter-failure intervals. The product is in its best condition before the first failure if repair is imperfect. After the imperfect repair, other inter-failure intervals which are explained by renewal processes, are stochastically smaller than the first inter-failure interval. Based on this idea, we suggest the failure-interval-failure-criterion model. In this model, we consider two random variables, X and Y where X represents failure intervals and Y represents failure criterion. We also obtain the distribution of the number of failures and conduct the warranty cost analysis. We investigate different types of warranty cost models, reliabilities and other measures for various systems including series-parallel configurations. Several numerical examples are discussed to demonstrate the applicability of the methodologies derived in the paper.

• IE interfaces
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• v.23 no.2
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• pp.176-181
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• 2010

Warranty claim data analysis is a useful tool for the manufacturer because it contains many useful informations regarding reliability of the product in the real-world environments. Because of the nature of uncertainty and the incompleteness of data, some bias patterns are observed on warranty claim rate known as 'spikes'. Two types of spikes are considered. One is due to manufacturing-related failures. The other is caused by customer's behavior. This paper proposes a model by considering two types of spikes. Warranty claim data is analyzed with the proposed model. To represent spikes observed on the early warranty period, we classify failures into manufacturing-related failures and usage-related failures. Uniform distribution is assumed for the time delayed to diagnose and report by customers. By reducing maximum value of the delayed time by customers, the proposed model characterizes customer's rush in the vicinity of the warranty expiration limit. Experimental results by using the real warranty claim data show that the proposed model is better than the existing one in respect to MSE(Mean Squared Error). Moreover it is expected to estimate the failure rate more realistically with proposed model because it considers the delayed time to diagnose and report by customers.

• Journal of the Korea Safety Management & Science
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• v.16 no.1
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• pp.139-146
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• 2014

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.

• Journal of the Korea Institute of Building Construction
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• v.17 no.4
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• pp.385-391
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• 2017

The warranty liability period for defects in apartment buildings by work type is not based on scientific analysis, making the appropriateness of the term a culprit behind the lawsuits. Therefore, this research aims to evaluate the appropriateness of the warranty liability term of apartment buildings by identifying the current status of defects, in particular, caused by finishing works. That is because the number of defects, caused during the finishing works, accounted for the largest portion of the total defect cases of apartment buildings reported to the Apartment Defect Dispute Mediation Committee under the Ministry of Land, Infrastructure, and Transport of Korea between 2010 and 2011. The result from analyzing claims for defect repairs of the finishing works showed that most cases by work type continued to be made after two years, and only about 60% were charged within the warranty period. And, defects by work type have correlation, which needs to be considered for a better construction technique. Considering a low correlation between the possibility of defects and the construction performance rankings, which are highly relevant to the apartment preference. It is believed that there needs to be a qualification process for agencies that actually performs finishing works.