FMEA is a systematic analysis of the systems to whatever level of detail is required to demonstrate that no single failure will cause an undesired event.
It is commonly defined as:
–“a systematic process for identifying potential design and process failures before they occur, with the intent to eliminate them or minimisethe risk associated with them”.
What are its objectives?
To identify potential design and process failures before they occur and to minimise the risk of failure by either proposing design changes or, if these cannot be formulated, proposing operational procedures. Essentially the FMEA is to:
–Identify the equipment or subsystem, mode of operation and the equipment;
–Identify potential failure modes and their causes;
–Evaluate the effects on the system of each failure mode;
–Identify measures for eliminating or reducing the risks associated with each failure mode;
–Identify trials and testing necessary to prove the conclusions; and
–Provide information to the operators and maintainers so that they understand
–the capabilities and limitations of the system to achieve best performance.
When is an FMEA carried out?
The FMEA should be commenced at the earliest stage that the design and development program will allow –even to assist at a higher level in identifying potential weaknesses during the conceptual design.
FMEA Emerged in the 1960‘s as a formal methodology in the aerospace and defense industries. In 1974, the Navy developed MIL-STD-1629 outlining a procedure for FMEA.
In the late 1970’s, automotive applications driven by liability costs, began to incorporate FMEA into the management of their processes.
Since then it has been adopted and standardized by many countries and industries
Many procedures partition the FMEA into several categories:
–System FMEA: an effective means of analyzing a design in terms of overall performance specifications, functions, interfaces, inputs, and outputs.
–Design FMEA identifies flaws in the specification of the design.
–Process FMEA specifies how manufacturing variation and errors might affect manufacturing efficiency and product functionality.
Often, the System and Design FMEA are combined into a comprehensive analysis covering product functionality.
Why perform an FMEA?
The thought process behind FMEA is implicit in any design effort: teams and individuals continuously ask “what could go wrong?” and “how could problems be prevented?”
FMEA is a way of documenting this thought process and making risks explicit. Some of the reasons for performing FMEA are:
–Improve Customer Satisfaction: help identify Customer Requirements (& how these might not be achieved), as well as improving reliability and safety in general.
–Provide Thoroughness: increase the likelihood that all potential failures and effects will be considered.
–Reduce Development Effort: reduce product development time and cost.
–Focus Test Planning: focus the development of test plans.
–Provide Documentation: make technical risks explicit to team members, suppliers, management.
Criticisms of FMEA
•FMEA is an established and prevalent design methodology, and yet it has also drawn some criticisms. Some documented criticisms of FMEA include:
–Performed too late, FMEA does not affect key product/process decisions (McKinney, 1991)
–FMEA does not capture key failures (Bednarz& Marriott, 1988)
–The analysis is not repeatable (Bell et al., 1992)
–FMEA is often an afterthought “checklist” exercise (Kara-Zaitriet al., 1991)
–Process is tedious (Ormsbyet al., 1992)
–The Risk Priority Number gives a distorted measure of risk (Gilchrist, 1993, Harpster1999)
•The Risk Priority Number (RPN) has evolved as an index used to prioritize failures in most FMEA standards. The RPN consists of three elements:
–Occurrence (O) –how likely is the cause to occur and result in the failure mode?
–Severity (S) –how serious are the end effects?
–Detection (D) –how likely is the failure to be detected before it reaches the customer?
These indices are usually rated on a 1-10 scale
•Is defined as how frequently the specific failure cause is projected to occur and result in the “failure mode”.
Is typically defined as an assessment of the seriousness of the potential “end effects,” and assessed independent of the causes.
Sometimes called Detectability, has no standard definition.
There is some confusion surrounding this index, since different definitions exist for this term.
If the team does not have a good understanding of this index, we recommend using a value of “1” for all fields and the team can fill it in later if time permits.
Detection case 1:
–Detection scores are generated on the basis of likelihood of detection by the relevant company design review and testing procedures program
–What is the chance of the customer catching the problem before the problem results in catastrophic failure
Once the risk has been foundactions are necessary.
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•Guidance on Failure Modes & Effects Analyses (FMEAs)
•Automotive Industry Action Group (AIAG)
•Potential Failure Mode and Effect Analysis, Reference Manual –4°edition