01-06-2012, 11:56 AM
failure modes and effects analysis (FMEA)
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History
Procedures for conducting FMECA were described in US Armed Forces Military Procedures document MIL-P-1629[2] (1949; revised in 1980 as MIL-STD-1629A).[3] By the early 1960s, contractors for the U.S. National Aeronautics and Space Administration (NASA) were using variations of FMECA or FMEA under a variety of names.[4][5] NASA programs using FMEA variants included Apollo, Viking,Voyager, Magellan, Galileo, and Skylab.[6][7][8] The civil aviation industry was an early adopter of FMEA, with the Society for Automotive Engineers publishing ARP926 in 1967.[9]
During the 1970's, use of FMEA and related techniques spread to other industries. In 1971 NASA prepared a report for the U.S. Geological Survey recommending the use of FMEA in assessment of offshore petroleum exploration.[10] FMEA as application for HACCP on the Apollo Space Program moved into the food industry in general.[11] In the late 1970s the Ford Motor Company introduced FMEA to the automotive industry for safety and regulatory consideration after the Pinto affair. They applied the same approach to processes (PFMEA) to consider potential process induced failures prior to launching production.
Although initially developed by the military, FMEA methodology is now extensively used in a variety of industries including semiconductor processing, food service, plastics, software, and healthcare.[12][13] It is integrated into the Automotive Industry Action Group's (AIAG) Advanced Product Quality Planning (APQP) process to provide risk mitigation, in both product and process development phases. Each potential cause must be considered for its effect on the product or process and, based on the risk, actions are determined and risks revisited after actions are complete.Toyota has taken this one step further with its Design Review Based on Failure Mode (DRBFM) approach. The method is now supported by the American Society for Quality which provides detailed guides on applying the method.[14]
Implementation
In FMEA, failures are prioritized according to how serious their consequences are, how frequently they occur and how easily they can be detected. A FMEA also documents current knowledge and actions about the risks of failures for use in continuous improvement. FMEA is used during the design stage with an aim to avoid future failures (sometimes called DFMEA in that case). Later it is used for process control, before and during ongoing operation of the process. Ideally, FMEA begins during the earliest conceptual stages of design and continues throughout the life of the product or service.
The outcomes of an FMEA development are actions to prevent or reduce the severity or likelihood of failures, starting with the highest-priority ones. It may be used to evaluate risk management priorities for mitigating known threat vulnerabilities. FMEA helps select remedial actions that reduce cumulative impacts of life-cycle consequences (risks) from a systems failure (fault).
It is used in many formal quality systems such as QS-9000 or ISO/TS 16949.
Using FMEA when designing
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FMEA is intended to provide an analytical approach to reviewing potential failure modes and their associated causes. FMEA is a recognised tool to help to assess which risks have the greatest concern, and therefore which risks to address in order to prevent problems before they arise. The development of these specifications helps to ensure the product will meet the defined requirements andcustomer needs.
The pre-work
The process for conducting an FMEA is typically developed in three main phases, in which appropriate actions need to be defined. Before starting with an FMEA, several other techniques are frequently employed to ensure that robustness and past history are included in the analysis.
A robustness analysis can be obtained from interface matrices, boundary diagrams, and parameter diagrams. Failures are often found from external 'noise factors' and from shared interfaces with other parts and/or systems.
Typically, a description of the system and its function is developed, considering both intentional and unintentional uses.
A block diagram of the system is often created for inclusion with the FMEA, giving an overview of the major components or process steps and how they are related. These are called logical relations around which the FMEA can be developed.
The primary FME document or 'worksheet' lists all of the items or functions of the system in a logical manner, typically based on the block diagram.