Reduce Warranty Costs Research Articles

Bayesian calculation of optimal burn-in policy for heterogeneous items under two-dimensional warranty

Various burn-in procedures have been greatly used to screen weak items and reduce warranty costs. This paper proposes a new burn-in model for heterogeneous items with non-renewing two-dimensional warranty. All failures within burn-in and warranty are assumed to be repaired through the minimal repair. Then we screen the items according to the failure information of the items during burn-in. We establish a cost-based model to optimize the mean total cost of each item put into the market. We demonstrate that the optimal burn-in time or usage rate should reach its upper bound under some conditions. In practice, the reliability and mean total cost of an item may be random due to the uncertainty of parameters in the model. Therefore, we also propose a Bayesian method to calculate the mean total cost and optimal burn-in policy of an item, which fully considers the uncertainty of parameters in the model. An example is also given to demonstrate the proposed burn-in model and Bayesian method.

Non-periodic preventive maintenance policies for complex multi-component products sold with loss-based two-dimensional warranties

Multi-component characteristics of complex industrial equipment, such as complex structures and stochastic dependencies, complicate analyzing the failure characteristics of such products and developing effective strategies to reduce warranty costs. In addition, a substantial customer loss or service interruption owing to the shutdown of these products forces manufacturers to formulate warranty contracts while considering customer loss. From the manufacturer’s perspective, with the aim of reducing the warranty costs while restraining the costs of customer loss, we propose the following two novel types of non-periodic imperfect preventive maintenance (PM) policies: unified and customized. The proposed PM policies simultaneously take into account the effects of customer usage rate heterogeneity and product deterioration on product failure. We characterize the failure relationship between the product and corresponding components based on the reliability block diagram and the Type I failure dependency model, and further construct the decision models for the proposed PM policies. The properties of the decision models are provided for certain special cases and are further used to design an algorithm for a general case. A comparison of the results of the numerical examples reveals the following: (1) Providing PM policies is beneficial for both the warranty providers and customers. The proposed PM policies are better than traditional periodic PM policies when shutdown loss costs are considered. (2) The stochastic dependencies will increase the costs of both the warranty and shutdown loss. It is necessary to take into account the stochastic dependencies of multi-component products when analyzing the warranty costs and formulating relevant decisions. (3) Beyond formulating effective PM policies, the manufacturer can mitigate the warranty cost pressure by adjusting the warranty coverage based on market information, or improving product reliability.

Customized Preventive Maintenance Strategies for Products Sold with Two-Dimensional Warranty

Two-dimensional warranty has played a significant role in improving product quality and competitiveness. However, two-dimensional basic warranty (BW) and extended warranty (EW) have not yet been combined effectively, and the customized maintenance strategies based on the consumers’ heterogeneity have been quite limited, which result in high maintenance costs. In this paper, the possibility of reducing warranty cost over BW and EW is explored by classifying customers based on their usage rates and then offering them with customized preventive maintenance (PM) strategies. By considering the purchasing ratio of EW contracts, the PM strategies for BW and EW are closely combined by the bi-level programming model. Numerical analysis is given to show the application of the proposed warranty strategy, and the significant findings and sensitivity of the main parameters are analyzed in the end. The findings demonstrate that the customized PM strategies combining BW and EW can effectively reduce warranty costs within the warranty period and provide a scientific guidance for manufacturers to design a more reasonable PM strategy.

Modern aspects of determining dental color in aesthetic dentistry

One of the important factors for creating a beautiful smile is the color of the teeth, which for most people has a more important role than anatomical characteristics. The exact reproduction of the color of the tooth affects the appearance and psycho-emotional state of the patient. The purpose of this work is to review domestic and foreign literature on methods for determining the color of teeth. Methods for determining color are divided into visual, spectrophotometric, colorimetric, digital photo analysis and computer method. The most common in the practice of a dentist is visual, which is based on comparing the examined tooth with color templates. Determination of the color of teeth using scales does not give a reliable result, which is due to the small number of shades in the colors, the phenomenon of metamerism, the impossibility of converting the obtained data into digital values, etc. The hardware method for determining the color of teeth compensates for the disadvantages of the visual and has a high adaptability, which requires many interrelated factors. Due to the complexity and high cost, the devices are used mainly for research purposes. Currently, innovative methods for determining the color of teeth, based on digital and computer analysis, are being actively developed. Thus, hardware methods for determining the color of teeth significantly increase the accuracy of choosing the shade of a future aesthetic restoration or orthopedic construction, excluding subjective factors, however, they require mandatory certification. Correct color assessment and identification helps to reduce costly re-treatments and reduce warranty costs. Despite this, visual methods using scales remain in demand among practicing doctors, due to their low cost and ease of use. The accuracy of determining the color of teeth in this case depends on the professionalism of the dentist, as well as on the correctness of the photo protocol.

Research on Pricing of Flexible Two-Dimensional Extended Warranty Considering Preventive Maintenance

Facing the uncertainty in transaction of two-dimensional extended warranty, a flexible pricing model is presented considering imperfect preventive maintenance combined with the degradation characteristics of item. The measure of two-dimensional preventive maintenance is carried out based on specified age interval or usage interval, the effect of imperfect preventive maintenance is described by age reduction model. The extended warranty cost is modeled from the perspective of manufacturer and customer, the method of gridding search is employed to optimize the maintenance strategy under different cases. Moreover, customized extended warranty price and warranty services are proposed on the basis of consumer usage rates. The results demonstrate that it is helpful to maximize the benefit of vendor by providing customized warranty strategy, the implementation of preventive maintenance during the whole warranty period can effectively reduce warranty cost for both sides.

A maintenance strategy for two-dimensional extended warranty based on dynamic usage rate

Maintenance strategies are commonly used for repairable products or items to reduce the warranty cost in the warranty coverage. This study proposes a new warranty maintenance strategy for two-dimensional extended warranty (EW) based on dynamic usage rate. Unlike previous studies that assumed a constant usage rate, the present study regards the consumer usage rate as dynamic in the two-dimensional EW coverage. A maintenance model is constructed to determine the optimal maintenance degree of warranty claim points and help service providers accurately estimate and reduce warranty cost. A numerical example of an automobile made in China is discussed to demonstrate the effectiveness of the proposed model. The formulated model can effectively reflect the changes in the consumer usage rate and thus helps service providers develop an accurate maintenance strategy. Meanwhile, the developed model can better reduce warranty cost compared with maintenance strategies with minimal repair.

Determination of the lead-acid battery's dynamic response using Butler-Volmer equation for advanced battery management systems in automotive applications

Abstract Micro-hybrid vehicles (μH) are currently starting to dominate the European market and seize constantly growing share of other leading markets in the world. On the one hand, the additional functionality of μH reduces the CO 2 emissions and improves the fuel economy, but, on the other hand, the additional stress imposed on the lead-acid battery reduces significantly its expected service life in comparison to conventional vehicles. Because of that μH require highly accurate battery state detection solutions. They are necessary to ensure the vehicle reliability requirements, prolong service life and reduce warranty costs. This paper presents an electrical model based on Butler-Volmer equation. The main novelty of the presented approach is its ability to predict accurately dynamic response of a battery considering a wide range of discharge current rates, state-of-charges and temperatures. Presented approach is fully implementable and adaptable in state-of-the-art low-cost platforms. Additionally, shown results indicate that it is applicable as a supporting tool for state-of-charge and state-of-health estimation and scalable for the different battery technologies and sizes. Validation using both static pulses and dynamic driving profile resulted in average absolute error of 124 mV regarding cranking current rate of 800 A respectively.

Capacity Fade of Lithium-Ion Batteries upon Mixed Calendar/Cycling Aging Protocol

Energy and power fade of lithium-ion batteries over time is a cause of complaints from Electric and Hybrid vehicles customers. Car manufacturers strive to improve accuracy of battery performance degradation predictions, in order to reduce warranty costs. Currently, these predictions are mainly based on accelerated aging tests in cycling mode or on calendar tests. However, testing protocols with combination of calendar and cycling modes representing the usage of a vehicle in real life application are not much used. In this paper, a mixed aging protocol combining cycling and calendar repetitive phases is elaborated. Experimental results obtained on a LIB technology are presented and discussed in comparison with conventional accelerated cycling tests at the same conditions.

Automotive Internal-Combustion-Engine Fault Detection and Classification Using Artificial Neural Network Techniques

In this paper, an engine fault detection and classification technique using vibration data in the crank angle domain is presented. These data are used in conjunction with artificial neural networks (ANNs), which are applied to detect faults in a four-stroke gasoline engine built for experimentation. A comparative study is provided between the popular backpropagation (BP) method, the Levenberg–Marquardt (LM) method, the quasi-Newton (QN) method, the extended Kalman filter (EKF), and the smooth variable structure filter (SVSF). The SVSF is a relatively new estimation strategy, based on the sliding mode concept. It has been formulated to efficiently train ANNs and is consequently referred to as the SVSF-ANN. The accuracy of the proposed method is compared with the standard accuracy of the Kalman-based filters and the popular BP algorithms in an effort to validate the SVSF-ANN performance and application to engine fault detection and classification. The customizable fault diagnostic system is able to detect known engine faults with various degrees of severity, such as defective lash adjuster, piston chirp (PC), and chain tensioner (CT) problems. The technique can be used at any dealership or assembly plant to considerably reduce warranty costs for the company and manufacturer.

PROBABILISTIC FATIGUE DESIGN OF SHAFT FOR BENDING AND TORSION

The ever increasing demand for better and reliable mechanical systems necessitates the explicit consideration of reliability in the modeling and design of these systems. Design for reliability (DFR) has been receiving a great deal of attention for several years and companies are deploying resources to the design for reliability process because of the need to satisfy customers and reduce warranty costs. In traditional or deterministic design, safety or design factors are usually subjectively assigned in product design so as to assure reliability. But this method of design does not provide a logical basis for addressing uncertainties, so the level of reliability cannot be assessed quantitatively. This paper presents a probabilistic design approach for shafts under combined bending and torsional loads using the generalized Gerber fatigue failure rule. The design model parameters are considered as random variables characterized by mean values and coefficients of variation (covs). The coefficient of variation of the shaft design model is obtained by using first order Taylor series expansion for strength and stress in a stress-life fatigue design. A reliability factor is defined and related to the covs of design parameters and a failure probability. The design model assumes a lognormal probability density distribution for the parameters. This approach thus accounts for variability of design model parameters and provides quantitative assessment of product reliability. The approach is flow-charted for ease of application. This study shows that deterministic engineering models can be transformed into probabilistic models that can predict the risk in a design situation. From the design examples considered, it is shown that the popular modified Goodman model (MGM) for stresslife fatigue design is slightly on the conservative side. The study indicates possible reduction in component size and hence savings in product cost can be obtained through probabilistic design. Probabilistic design seems to be the most practical approach in product design due to the inherent variability associated with service loads, material properties, geometrical attributes, and mathematical design models. The computations in the present model were done using Microsoft Excel. This demonstrates that probabilistic design can be simplified so that specialized software and skills may not be required, especially at the preliminary design phase. Very often, available probabilistic models are intensive in numerical computation, requiring custom software and skilled personnel. The model approach presented needs to be explored for other design applications, so as to the make probabilistic design a common practice.

Modeling and analysis of effective ways for improving the reliability of second-hand products sold with warranty

Often, customers are uncertain about the performance and durability of the used/second-hand products. The warranties play an important role in reassuring the buyer. Offering the warranty implies that the dealer incurs additional costs to service any claims made by the customers. Reducing warranty costs is an issue of great interest to dealers. One way of improving the reliability and reducing the warranty servicing cost for second-hand items is through actions such as overhaul and upgrade which are carried out by the dealer or a third party. Improving actions allow the dealer to offer better warranty terms and to sell the item at a higher price. This paper deals with two effective approaches (virtual age approach and screening test approach) to decide on the reliability improvement strategies for second-hand products sold under various warranty policies (failure-free, rebate warranty, and a combination of free replacement and lump sum). A numerical example illustrates that from a dealer’s point of view, it is beneficial to carry out an improvement action only if the reduction in the warranty servicing cost is greater than the extra cost incurred due to this improvement action.

Warranty servicing strategies to improve customer satisfaction

Customer satisfaction with a purchased product depends on its performance under warranty and during the remainder of its useful life. Dissatisfaction with an item is important to a manufacturer since it can lead to the loss of potential customers through the negative word‐of‐mouth effect as well as existing customers switching to a competitor. In this paper, we define satisfaction in terms of the likelihood of a customer not switching to a different manufacturer when a new item needs to be purchased. Manufacturers can use specific servicing strategies to reduce warranty costs and this topic has already been addressed in the literature without considering the effect of customer dissatisfaction. In this paper, we propose particular strategies that will increase customer satisfaction and we discuss methods for obtaining the optimal parameters of these strategies.

Reinventing warranty at HP: an engineering approach to warranty

The mechanisms used to understand and reduce warranty costs often focus exclusively on the analysis of product failures. However, warranty costs can also be incurred by events such as support calls that do not involve a product failure. We describe a method used by a major electronics manufacturer to understand warranty costs by modeling warranty events. Furthermore, event modeling that uses a time-dependent warranty event rate instead of the more standard average rate of failure allows the improved prediction of warranty costs and better accruals. As a result of the modeling, warranty engineers can help product managers more accurately predict the costs associated with removing certain warranty events, changing warranty policies and offering extended warranties for their electronic products. Copyright © 2003 John Wiley & Sons, Ltd.