改善傳統失效模式與效應分析的風險優先數

Abstract

失效模式與效應分析(Failure Modes and Effects Analysis, FMEA)是一項用來 改善品質和提高產品生產可靠性的重要風險評估工具。近年來，失效模式與效 應分析已經被廣泛地應用於各個產業。在傳統的失效模式與效應分析中，風險 優先數(Risk Priority Number, RPN)被用來排序和評估各失效模式的潛在失效效應，而使用者依嚴重度(S)、發生度(O)、可偵測度(D)對各效應評分，此三項評分的乘積即為 RPN，範圍從 1 到 1,000。然而，傳統的風險優先數方法有其缺點，例如：未考慮三項評分參數之權重、RPN 有許多重複數、衡量尺度的問題。為了改善傳統風險優先數的缺點並且增進風險評估的能力，本研究提出一個有效且簡單的新指標來取代傳統風險優先數，並將此新指標命名為 MRPN(modified RPN)；此指標運用指數相加的數學方程式取代原本直接將三個衡量因子相乘的RPN。此外，運用實務上的案例來說明本研究所建立的 MRPN 方法不僅可以改善了傳統風險優先數的問題，並能得到更正確且合理的風險評估結果。

Failure modes and effects analysis (FMEA) is one of the important risk assessment tools for improving quality and reliability of products. It has been extensively used in various applications in recent years. The risk priority number (RPN) is the classical method to rank failure modes in conventional FMEA. RPN, which ranges from 1 to 1000, is a mathematical product of three parameters - severity (S), occurrence (O), and detection (D) - to rank and assess the risk of potential failure modes. However, there are some shortcomings of conventional RPN method, such as having too many duplicate numbers, performing incorrect mathematical operations with the measurement scales, and treating each risk factor equally important in terms of risk. In order to improve the shortcomings of conventional RPN method and to enhance the risk evaluation capability of FMEA, this study presents an easy yet effective method to describe the degree of risk of each potential failure mode. The new method is named as modified risk priority number (MRPN) which uses a simple addition function to the exponential form of S, O, and D to substitute the conventional RPN method which is a mathematical product of three parameters. Two practical cases are used to demonstrate that the MRPN method can not only resolve some problems of the conventional RPN method but also is able to provide a more accurate and reasonable risk assessment in FMEA.