An integrated structural framework to cost-based FMECA: The priority-cost FMECA

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Abstract

The Failure Mode, Effects and Criticality Analysis (FMECA) methodology is a widely recognized tool for the study and reliability analysis of a design or process. Many authors in the field have emphasized the usefulness of this particular method as well as its limitations. In particular, there are two main criticisms regarding the Risk Priority Number (RPN) method of calculation and the extreme difficulty in considering the variable of the corrective action cost in the analysis. The main scope of this work is to present a new integrated approach, named priority-cost FMECA (PC-FMECA), in order to exceed these limits. Making reference to a paper by Braglia [MAFMA: multi-attribute failure modes analysis. Int J Qual Reliab Manage 2000; 17(9)], this study proposes a method which allows for the calculation of a new RPN and the introduction of the concept of Profitability taking into consideration the corrective action cost. The study is divided in three fundamental phases: critical analysis of the FMECA model, proposal and development of the PC-FMECA and presentation of an implemented case study in the automotive field.

Introduction

In the present day, customer requirements and increasing product complexity have made the concept of reliability a factor of critical importance in the planning of all mechanical, electronic, electromechanical systems and devices. The term reliability refers to the probability of a component or system to carry out the required functions under particular conditions of use and for a certain period of time. A company which focuses on reliability, clearly putting emphasis on its aim to guarantee customer satisfaction with its products and services, distinguishes itself in the market. Products and services with increased value are undoubtedly more competitive and have a much greater chance of commercial success. Reliability is an issue of relevance for a system's entire life-span: planning, development, production, quality control, shipment, installation, operating activity and maintenance [1]. For this reason, it was necessary to express reliability in quantitative terms, by way of a mathematical model that could be applied to the whole system and through the analysis of performance in realistic operating conditions. The Failure Modes, Effects and Criticality Analysis, known as FMECA, was created and developed in the United States in the early 1960s and used by NASA during the development of the Apollo Project. It was then adopted in the automotive field with the Ford Motor Company subsequently improving and upgrading certain aspects. The FMECA process implementation was standardized by the MIL-STD 1629-A in 1988. The aim of this work is to propose an integrated structural framework to implement a FMECA project in terms of cost, in order to select the corrective action, with a given budget, in not-safety-critical-cases. The following section provides a brief explanation of the FMECA, highlighting the limits and point of weakness concerning cost evaluation and method for selecting corrective actions. The proposed model is presented in 3 The new approach: the priority-cost FMECA (PC-FMECA), 4 The case study reports an applied case study.

Section snippets

FMECA: point of weakness

The FMECA is a bottom-up method for analysing reliability, which, during a system's design stage, is confronted with examination and highlighting:

  • all possible failure modes;

  • all causes of failures;

  • effects produced by failures;

  • possible solutions.

This method relies on its ability to quantify certain characteristics and important parameters. These latter, opportunely combined, allow for identifying critical elements and defining certain intervention priorities.

The FMECA takes three parameters into

The new approach: the priority-cost FMECA (PC-FMECA)

In order to develop the new approach, it is necessary to present a methodology which correlates the potential failure to its fundamental economic aspects. This methodology, presented in the next paragraph, will be analysed in order to exceed its limits. The new approach will be then presented.

The case study

In order to validate the introduced approach a case study is implemented in a primary organization of the automotive field. The interest of the study has been focused on any potential failures of a fuel system components: the electro-injector (Fig. 7).

The design team has selected six potential failures.

  • Failure Mode 1: Flow value to high.

  • Failure Mode 2: No phasing definition.

  • Failure Mode 3: Sudden malfunction of degradation of spray angle/penetration/atomization.

  • Failure Mode 4: Spray

Conclusion

The two main aims of this work are: (i) realization of a model based on costs for the FMECA and (ii) realization of a method to select the best mix of failures to be repaired with respect to the budget made available by the firm. The first objective has been accomplished considering how many authors have criticized the classical approach to the FMECA. The problems of the traditional analysis have been solved through a new interpretation of the parameters which took part in the realization of

Acknowledgments

The author would like to thank the referees of the review, for their valuable suggestions and useful comments that made possible to greatly improve the structure and the quality of this paper.

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