Includes: Design Failure Mode and Effects Analysis (DFMEA)
Process Failure Mode and Effects Analysis (PFMEA)
Failure Mode and Effects Analysis (FMEA) is a structured
methodology for identifying failures, errors, and defects before they occur and
prioritizing them for corrective action. Throughout this guidelines document,
the applicability of two types of FMEA have been discussed. These are Design
Failure Mode and Effects Analysis (DFMEA) and Process Failure Mode and Effects
Analysis (PFMEA). DFMEA is a means of analyzing the part design for potential
failures, errors, and defects prior to the first production run. PFMEA helps to
analyze the part's manufacturing processes prior to production to identify
possible process failures that can induce defects into the part. In both
methodologies, the goal is the same - early identification of and reduction or,
ideally, elimination of failure mechanisms.
FMEA is a bottoms-up approach to failure identification.
It should begin with the lowest level of detail and continue until the entire
system has been analyzed. From a product standpoint, lowest level parts are
first analyzed, followed by components, assemblies, subsystems, and, finally,
systems. It is only through this thorough analysis of the whole system, part by
part, that FMEA is most effective.
FMEA, whether DFMEA or PFMEA, should be an iterative
process and should be used throughout the integrated product and process
development cycle. Design FMEA or DFMEA should first be performed during
conceptual design and then periodically as the design matures. Information from
subsequent DFMEAs helps to further refine the design to ensure that failure
mechanisms have been eliminated or controlled to the greatest extent possible
prior to production of the product. Process FMEAs or PFMEAs can first be
performed to more thoroughly understand a process capability and, as the design
matures for a particular product, to analyze the effects of the process on that
particular product. Additionally, both DFMEA and PFMEA can be used once failures
have occurred in production to identify problems and aid in determining
corrective action. As applied to producibility, FMEA should be utilized as a
basis for continuous improvement.
To illustrate the concept of FMEA and how one is
performed, an example DFMEA is provided in Figure
F.3. A PFMEA, however, is
similar and works in the same way. The first step is to identify, by a unique
identifier, each part or component in the system, starting with the lowest level
detail (A). The functions that each part performs and one or two failure modes
for each function are listed in (B) and (C) respectively. The effects that each
failure mode would have (especially as observed by the customer) (D) and the
causes of the failure (E) are then detailed. A risk assessment, taking into
account the severity of the failure (F), the frequency of occurrence (G), and
the ease of failure detection (H), is performed by assessing each on a
pre-determined scale (often 1 to 10). These ratings for severity, occurrence,
and detection are then multiplied together to get a Risk Priority Number (RPN),
which identifies the level of risk for each part (I). Pareto analysis of the
RPNs can then determine which parts or failure modes are most important to
concentrate on first. The relative rankings of severity, occurrence, and
detection identify what should be targeted for improvement to provide the
biggest payoff. The corrective or preventative action that should be taken to
eliminate or reduce the failure is listed in (J) and the responsible party and
the date when the action should be accomplished by in (K) and (L) respectively.
After the corrective action is accomplished, the risk assessment is performed
once more (M-P) to ensure that the corrective action did, in fact, reduce the
risk of failure.
From a producibility standpoint, the key to successful
use of FMEA is to perform it throughout the integrated product and process
design cycle - as the design matures and is finalized and as the processes are
locked in for production of the product. It is important to perform FMEA (both
DFMEA and PFMEA) with each major change in design to ensure that new failure
modes have not been introduced during design refinement as well as after a part
is in production to identify any failure modes that were overlooked prior to
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Palady, P. (1995). Failure Modes and Effects Analysis. PT Publications, Incorporated.
Palady, P. (1999). FMEA: The Author's Edition - Exclusive New Developments Approved for the Federal Standard. Practical Applications.
Resource Engineering, Inc. Staff. (1998). FMEA Investigator Workbook. Resource Engineering.
Rochester Institute of Technology. (1997). Failure Mode and Effects Analysis. Rochester, NY: Rochester Institute of Technology.