|
FMEA (Failure Modes and Effects Analysis) is a systematic method used to investigate and evaluate the potential failure of a product or a process. For each failure mode, the team assesses the severity, the likelihood of occurrence, and the difficulty of detection of the failure mode. These are ranked in numbers between 1 and 10. The product of these numbers is called the Risk Priority Number (RPN). Actions are developed to reduce the RPN, which are then recommended. Priority is given to the highest RPN value and severity value. The traditional FMEA technique has limitations when, two or more failure modes have the same RPN and the team has a disagreement in the ranking scale for severity, occurrence and detection. This paper presents a new approach to overcome these limitations while evaluating RPN in Design FMEA.
FMEA (Failure Modes and Effects Analysis) is a proactive analysis tool, allowing engineers to anticipate failure modes before they happen or before a new product or a process is released. It also helps the engineer in preventing the negative effects of these failure modes, from reaching the customer, primarily by eliminating their causes and increasing the chances of detecting them before they can do any damage (Paul, 1995). The first step in the FMEA process is to break down a system or a process into discrete elements. In the case of hardware, a system even as large as an airplane can be broken down into a number of assemblies or subsystems and ultimately into individual components. The level of hierarchical breakdown can be carried up to any level desired by the analyst. Once the breakdown is complete, the next step is to determine the ways in which each element could potentially fail.
Then, each failure mode is evaluated independently and a determination is made as to what the effect of that failure would be at the current level. After that, the resulting effect on the entire system is calculated. For each failure mode, the team assesses the severity, the likelihood of occurrence, and the difficulty of detection of the failure mode. The assessment is done on a scale of 1 to 10. The product of these numbers is called the Risk Priority Number (RPN). These numbers are used to indicate the parts or the processes that need improvement. Depending on the policy of the company, different criteria are used to trigger improvement actions to reduce the RPN value (Cherrill and Seung, 2002). |
