FMEA is a systematic set of activities intended to help a designer or engineer to analyze the design of a system (product or process) to assure that, to the extent possible, potential failures, their associated causes, and their potential effects have been considered and addressed. The goals of FMEA are to:
Failure Mode
The value of a FMEA is in the structured review of the design using a cross disciplinary team to identify potential failures and the associated causes so that they may be remedied. A FMEA document is created as a tool to organize the review to minimize potential for missing something and to document the results of the review. Documentation of the results aids in follow-up and "closing the analysis" by showing actions taken and providing documentation that the risk has been mitigated.
Enter the name and number of the item being analyzed. Use the nomenclature and show the design level as indicated on the engineering drawing. Prior to initial release, experimental numbers should be used. Enter, as concisely as possible, the function of the item being analyzed to meet the design intent. Include information regarding the environment in which this system operates (e.g., define temperature, pressure, humidity ranges). If the item has more than one function with different potential modes of failure, list all the functions separately.
Potential Failure Mode is defined as the manner in which a component, subsystem, or system could potentially fail to meet the design intent. The potential failure mode may also be the cause of a potential failure mode in a higher level subsystem, or system, or be the effect of one in a lower level component. List each potential failure mode for the particular item and item function. The assumption is made that the failure could occur, but may not necessarily occur. A recommended starting point is a review of past things-gone-wrong, concerns, reports, and group brainstorming. Potential failure modes that could only occur under certain operating conditions (i.e., hot, cold, dry, dusty, etc.) and under certain usage conditions (i.e., above average mileage, rough terrain, only city driving, etc.) should be considered. Typical failure modes could be, but are not limited to:
Potential Effects of Failure are defined as the effects of the failure mode on the function, as perceived by the customer. Describe the effects of the failure in terms of what the customer might notice or experience, remembering that the customer may be an internal customer as well as the ultimate end user. State clearly if the function could impact safety or noncompliance to regulations. The effects should always be stated in terms of the specific system, subsystem, or component being analyzed. Remember that a hierarchical relationship exists between the component, subsystem, and system levels. For example, a part could fracture, which may cause the assembly to vibrate, resulting in an intermittent system operation. The intermittent system operation could cause performance to degrade, and ultimately lead to customer dissatisfaction. The intent is to forecast the failure effects to the Team's level of knowledge. Typical failure effects could be, but are not limited to:
Severity is an assessment of the seriousness of the effect (listed in the previous column) of the potential failure mode to the next component, subsystem, system, or customer if it occurs. Severity applies to the effect only. A reduction in Severity Ranking index can be effected only through a design change. Severity should be estimated on a "1" to "10" scale.
Potential Cause of Failure is defined as an indication of a design weakness, the consequence of which is the failure mode. List, to the extent possible, every conceivable failure cause and/or failure mechanism for each failure mode. The cause/mechanism should be listed as concisely and completely as possible so that remedial efforts can be aimed at pertinent causes. Typical failure causes may include, but are not limited to:
Occurrence is the likelihood that a specific cause/mechanism (listed in the previous column) will occur. The likelihood of occurrence ranking number has a meaning rather than a value. Removing or controlling one or more of the causes/mechanisms of the failure mode through a design change is the only way a reduction in the occurrence can be effected. Estimate the likelihood of occurrence of potential failure cause/mechanism on a "1" to "10" scale. In determining this estimate, questions such as the following should be considered:
A consistent occurrence ranking system should be used to ensure continuity. The "Design Life Possible Failure Rates" are based on the number of failures that are anticipated during the design life of the component, subsystem, or system. The occurrence ranking number is related to the rating scale and does not reflect the actual likelihood of occurrence.
List the prevention, design validation/verification (DV), or other activitiesthat will assure the design adequacy for the failure mode and/or cause/mechanism under consideration. Current controls (e.g., road testing, design reviews, fail/safe (pressure relief valve), mathematical studies, rig/lab testing, feasibility review, prototype tests, fleet testing) are those that have been or are being used with the same or similar designs. There are three types of Design Controls/features to consider, those that:
The preferred approach is to first use type (1) controls if possible; second, use the type (2) controls; and third, use the type (3) controls. The initial occurrence rankings will be affected by the type (1) controls provided they are integrated as part of the design intent. The initial detection rankings will be based on the type (2) or type (3) current controls, provided the prototypes and models being used are representative of design intent.
Detection is an assessment of the ability of the proposed type (2) current design controls, listed in column 16, to detect a potential cause/mechanism (design weakness), or the ability of the proposed type (3) current design controls to detect the subsequent failure mode, before the component, subsystem, or system is released for production. In order to achieve a lower ranking, generally the planned design control (e.g., preventative, validation, and/or verification activities) has to be improved.
When the failure modes have been rank ordered by RPN, corrective action should be first directed at the highest ranked concerns and critical items. The intent of any recommended action is to reduce any one or all of the occurrence, severity, and/or detection rankings. An increase in design validation/verification actions will result in a reduction in the detection ranking only. A reduction in the occurrence ranking can be effected only by removing or controlling one or more of the causes/mechanisms of the failure mode through a design revision. Only a design revision can bring about a reduction in the severity ranking. Actions such as the following should be considered, but are not limited to:
Typically, FMEA is used to identify technical failures with the product, and not necessarily failures that may result from misuse or unintended uses of the product. However, FMEA may also be used to identify possible uses and scenarios that could cause failures and/or damaging effects. For example, users with a range of possible levels cognitive and physical abilities, users in situations that reduce attention on the task of interacting with the product or require unusually quick judgment, or users that interact with the product in ways not planned by the designer may result in severe consequences that could be avoided with good design. One simple illustrative example is the laundry detergent product "Fabuloso", which was packaged, colored and even scented in a way that looks similar to popular beverages. Curious non-Spanish-speaking patrons who were unable to read the label but who purchased the product to try it resulted in over 100 cases of accidental ingestion that could have been avoided with good design.
Adds value by assessing product-design risk reduction as a result of monitoring and response. FMEA-MSR evaluates the current state of risk of failure and derives the necessity for additional monitoring by comparison with the conditions for acceptable residual risk.
There are a number of published guidelines and standards for the requirements and recommended reporting format of failure mode and effects analyses. Some of the main published standards for this type of analysis include SAE J1739, AIAG FMEA-4 and MIL-STD-1629A. In addition, many industries and companies have developed their own procedures to meet the specific requirements of their products/processes. As an example, Figure 1 shows a sample Process FMEA (PFMEA) in the Automotive Industry Action Group (AIAG) FMEA-4 format.
A typical failure modes and effects analysis incorporates some method to evaluate the risk associated with the potential problems identified through the analysis. The two most common methods, Risk Priority Numbers and Criticality Analysis, are described next.
Note: The quantitative criticality analysis in ReliaSoft's software tools (XFMEA and RCM++) is patterned after the concepts in MIL-STD-1629A but modified to use a more general approach that overcomes several inherent limitations and simplifications present in MIL-STD-1629A (including the assumption of a constant failure rate). For specific details on this approach, see _Analysis.
The Failure Modes, Effects and Criticality Analysis (FMEA / FMECA) procedure is a tool that has been adapted in many different ways for many different purposes. It can contribute to improved designs for products and processes, resulting in higher reliability, better quality, increased safety, enhanced customer satisfaction and reduced costs. The tool can also be used to establish and optimize maintenance plans for repairable systems and/or contribute to control plans and other quality assurance procedures. It provides a knowledge base of failure mode and corrective action information that can be used as a resource in future troubleshooting efforts and as a training tool for new engineers. In addition, an FMEA or FMECA is often required to comply with safety and quality requirements, such as ISO 9001, QS 9000, ISO/TS 16949, Six Sigma, FDA Good Manufacturing Practices (GMPs), Process Safety Management Act (PSM), etc. 2ff7e9595c
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