s**********8
发帖数: 25265 | 1 Failure mode and effects analysis
From Wikipedia,
A failure modes and effects analysis (FMEA) is a procedure in product
development and operations management for analysis of potential failure
modes within a system for classification by the severity and likelihood of
the failures. A successful FMEA activity helps a team to identify potential
failure modes based on past experience with similar products or processes,
enabling the team to design those failures out of the system with the
minimum of effort and resource expenditure, thereby reducing development
time and costs. It is widely used in manufacturing industries in various
phases of the product life cycle and is now increasingly finding use in the
service industry. Failure modes are any errors or defects in a process,
design, or item, especially those that affect the customer, and can be
potential or actual. Effects analysis refers to studying the consequences of
those failures.
Contents [hide]
1 Basic terms[1]
2 History
3 Implementation
4 Using FMEA when designing
4.1 The pre-work
4.2 Step 1: Occurrence
4.3 Step 2: Sensitivity
4.4 Step 3: Detection
4.5 Risk Priority Number (RPN)
5 Timing of FMEA
6 Uses of FMEA
7 Advantages
8 Limitations
9 Software
10 Types of FMEA
11 See also
12 Notes
13 External links
[edit] Basic terms[1]
FMEA cycle.Failure
"The LOSS of an intended function of a device under stated conditions."
Failure mode
"The manner by which a failure is observed; it generally describes the way
the failure occurs."
Failure effect
Immediate consequences of a failure on operation, function or functionality,
or status of some item
Indenture levels
An identifier for item complexity. Complexity increases as levels are closer
to one.
Local effect
The Failure effect as it applies to the item under analysis.
Next higher level effect
The Failure effect as it applies at the next higher indenture level.
End effect
The failure effect at the highest indenture level or total system.
Failure cause
Defects in design, process, quality, or part application, which are the
underlying cause of the failure or which initiate a process which leads to
failure.
Severity
"The consequences of a failure mode. Severity considers the worst potential
consequence of a failure, determined by the degree of injury, property
damage, or system damage that could ultimately occur."
[edit] HistoryLearning from each failure is both costly and time consuming,
and FMEA is a more systematic method of studying failure. As such, it is
considered better to first conduct some thought experiments.
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] Later it was used for aerospace/rocket development to avoid errors in
small sample sizes of costly rocket technology. An example of this is the
Apollo Space program. It was also used as application for HACCP for the
Apollo Space Program, and later the food industry in general.[4] The primary
push came during the 1960s, while developing the means to put a man on the
moon and return him safely to earth. 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.[5][6] 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.[7]
[edit] ImplementationIn 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.
[edit] Using FMEA when designingFMEA can provide an analytical approach,
when dealing with potential failure modes and their associated causes. When
considering possible failures in a design – like safety, cost, performance,
quality and reliability – an engineer can get a lot of information about
how to alter the development/manufacturing process, in order to avoid these
failures. FMEA provides an easy tool to determine which risk has the
greatest concern, and therefore an action is needed to prevent a problem
before it arises. The development of these specifications will ensure the
product will meet the defined requirements and customer needs.
[edit] The pre-workThe process for conducting an FMEA is straightforward. It
is developed in three main phases, in which appropriate actions need to be
defined. But before starting with an FMEA, it is important to complete some
pre-work to confirm that robustness and past history are included in the
analysis.
A robustness analysis can be obtained from interface matrices, boundary
diagrams, and parameter diagrams. Many failures are due to noise factors and
shared interfaces with other parts and/or systems, because engineers tend
to focus on what they control directly.
To start it is necessary to describe the system and its function. A good
understanding simplifies further analysis. This way an engineer can see
which uses of the system are desirable and which are not. It is important to
consider both intentional and unintentional uses. Unintentional uses are a
form of hostile environment.
Then, a block diagram of the system needs to be created. This diagram gives
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. It is useful to create a coding system to identify the different
system elements. The block diagram should always be included with the FMEA.
Before starting the actual FMEA, a worksheet needs to be created, which
contains the important information about the system, such as the revision
date or the names of the components. On this worksheet all the items or
functions of the subject should be listed in a logical manner, based on the
block diagram.
Example FMEA Worksheet Item / Function Potential Failure mode Potential
Effects of Failure S (severity rating) Potential Cause(s) O (occurrence
rating) Current controls D (detection rating) CRIT (critical characteristic
RPN (risk priority number) Recommended actions Responsibility and target
completion date Action taken New S New O New D New RPN
Fill tub High level sensor never trips Liquid spills on customer floor 8
level sensor failed
level sensor disconnected 2 Fill timeout based on time to fill to low level
sensor 5 N 80 Perform cost analysis of adding additional sensor halfway
between low and high level sensors Jane Doe
10-June-2011
[edit] Step 1: OccurrenceIn this step it is necessary to look at the cause
of a failure mode and the number of times it occurs. This can be done by
looking at similar products or processes and the failure modes that have
been documented for them. A failure cause is looked upon as a design
weakness. All the potential causes for a failure mode should be identified
and documented. Again this should be in technical terms. Examples of causes
are: erroneous algorithms, excessive voltage or improper operating
conditions. A failure mode is given an occurrence ranking (O), again 1–10.
Actions need to be determined if the occurrence is high (meaning > 4 for non
-safety failure modes and > 1 when the severity-number from step 1 is 1 or 0
). This step is called the detailed development section of the FMEA process.
Occurrence also can be defined as %. If a non-safety issue happened less
than 1%, we can give 1 to it. It is based on your product and customer
specification.
Rating Meaning
1 No effect
2/3 Low (relatively few failures)
4/5/6 Moderate (occasional failures)
7/8 High (repeated failures)
9/10 Very high (failure is almost inevitable)
[8]
[edit] Step 2: SensitivityDetermine all failure modes based on the
functional requirements and their effects. Examples of failure modes are:
Electrical short-circuiting, corrosion or deformation. A failure mode in one
component can lead to a failure mode in another component, therefore each
failure mode should be listed in technical terms and for function. Hereafter
the ultimate effect of each failure mode needs to be considered. A failure
effect is defined as the result of a failure mode on the function of the
system as perceived by the user. In this way it is convenient to write these
effects down in terms of what the user might see or experience. Examples of
failure effects are: degraded performance, noise or even injury to a user.
Each effect is given a sensitivity number (S) from 1 (no danger) to 10 (
critical). These numbers help an engineer to prioritize the failure modes
and their effects. If the sensitivity of an effect has a number 9 or 10,
actions are considered to change the design by eliminating the failure mode,
if possible, or protecting the user from the effect. A sensitivity rating
of 9 or 10 is generally reserved for those effects which would cause injury
to a user or otherwise result in litigation.
Rating Meaning
1 No effect
2 Very minor (only noticed by discriminating customers)
3 Minor (affects very little of the system, noticed by average customer)
4/5/6 Moderate (most customers are annoyed)
7/8 High (causes a loss of primary function; customers are dissatisfied)
9/10 Very high and hazardous (product becomes inoperative; customers angered
; the failure may result unsafe operation and possible injury)
[8]
[edit] Step 3: DetectionWhen appropriate actions are determined, it is
necessary to test their efficiency. In addition, design verification is
needed. The proper inspection methods need to be chosen. First, an engineer
should look at the current controls of the system, that prevent failure
modes from occurring or which detect the failure before it reaches the
customer. Hereafter one should identify testing, analysis, monitoring and
other techniques that can be or have been used on similar systems to detect
failures. From these controls an engineer can learn how likely it is for a
failure to be identified or detected. Each combination from the previous 2
steps receives a detection number (D). This ranks the ability of planned
tests and inspections to remove defects or detect failure modes in time. The
assigned detection number measures the risk that the failure will escape
detection. A high detection number indicates that the chances are high that
the failure will escape detection, or in other words, that the chances of
detection are low.
Rating Meaning
1 Almost certain
2 High
3 Moderate
4/5/6 Moderate - most customers are annoyed
7/8 Low
9/10 Very remote to absolute uncertainty
[8]
After these three basic steps, risk priority numbers (RPN) are calculated
[edit] Risk Priority Number (RPN)RPN play an important part in the choice of
an action against failure modes. They are threshold values in the
evaluation of these actions.
After ranking the severity, occurrence and detectability the RPN can be
easily calculated by multiplying these three numbers: RPN = S × O × D
This has to be done for the entire process and/or design. Once this is done
it is easy to determine the areas of greatest concern. The failure modes
that have the highest RPN should be given the highest priority for
corrective action. This means it is not always the failure modes with the
highest severity numbers that should be treated first. There could be less
severe failures, but which occur more often and are less detectable.
After these values are allocated, recommended actions with targets,
responsibility and dates of implementation are noted. These actions can
include specific inspection, testing or quality procedures, redesign (such
as selection of new components), adding more redundancy and limiting
environmental stresses or operating range. Once the actions have been
implemented in the design/process, the new RPN should be checked, to confirm
the improvements. These tests are often put in graphs, for easy
visualization. Whenever a design or a process changes, an FMEA should be
updated.
A few logical but important thoughts come in mind:
Try to eliminate the failure mode (some failures are more preventable than
others)
Minimize the severity of the failure
Reduce the occurrence of the failure mode
Improve the detection
[edit] Timing of FMEAThe FMEA should be updated whenever:
At the beginning of a cycle (new product/process)
Changes are made to the operating conditions
A change is made in the design
New regulations are instituted
Customer feedback indicates a problem
[edit] Uses of FMEADevelopment of system requirements that minimize the
likelihood of failures.
Development of methods to design and test systems to ensure that the
failures have been eliminated.
Evaluation of the requirements of the customer to ensure that those do not
give rise to potential failures.
Identification of certain design characteristics that contribute to failures
, and minimize or eliminate those effects.
Tracking and managing potential risks in the design. This helps avoid the
same failures in future projects.
Ensuring that any failure that could occur will not injure the customer or
seriously impact a system.
To produce world class quality products
[edit] AdvantagesImprove the quality, reliability and safety of a product/
process
Improve company image and competitiveness
Increase user satisfaction
Reduce system development timing and cost
Collect information to reduce future failures, capture engineering knowledge
Reduce the potential for warranty concerns
Early identification and elimination of potential failure modes
Emphasize problem prevention
Minimize late changes and associated cost
Catalyst for teamwork and idea exchange between functions
Reduce the possibility of same kind of failure in future
Reduce impact of profit margin company
Reduce possible scrap in production
[edit] LimitationsSince FMEA is effectively dependent on the members of the
committee which examines product failures, it is limited by their experience
of previous failures. If a failure mode cannot be identified, then external
help is needed from consultants who are aware of the many different types
of product failure. FMEA is thus part of a larger system of quality control,
where documentation is vital to implementation. General texts and detailed
publications are available in forensic engineering and failure analysis. It
is a general requirement of many specific national and international
standards that FMEA is used in evaluating product integrity. If used as a
top-down tool, FMEA may only identify major failure modes in a system. Fault
tree analysis (FTA) is better suited for "top-down" analysis. When used as
a "bottom-up" tool FMEA can augment or complement FTA and identify many more
causes and failure modes resulting in top-level symptoms. It is not able to
discover complex failure modes involving multiple failures within a
subsystem, or to report expected failure intervals of particular failure
modes up to the upper level subsystem or system.[citation needed]
Additionally, the multiplication of the severity, occurrence and detection
rankings may result in rank reversals, where a less serious failure mode
receives a higher RPN than a more serious failure mode.[9] The reason for
this is that the rankings are ordinal scale numbers, and multiplication is
not defined for ordinal numbers. The ordinal rankings only say that one
ranking is better or worse than another, but not by how much. For instance,
a ranking of "2" may not be twice as bad as a ranking of "1," or an "8" may
not be twice as bad as a "4," but multiplication treats them as though they
are. See Level of measurement for further discussion.
[edit] SoftwareMost FMEAs are created as a spreadsheet. Specialized FMEA
software packages exist that offer some advantages over spreadsheets.
[edit] Types of FMEAProcess: analysis of manufacturing and assembly
processes
Design: analysis of products prior to production
Concept: analysis of systems or subsystems in the early design concept
stages
Equipment: analysis of machinery and equipment design before purchase
Service: analysis of service industry processes before they are released to
impact the customer
System: analysis of the global system functions
Software: analysis of the software functions
[edit] See alsoFailure Mode, Effects, and Criticality Analysis (FMECA)
Causal layered analysis
Futures techniques
Failure mode
Failure rate
Forensic engineering
High availability
Process decision program chart
Hazard Analysis and Critical Control Points
Quality control
Reliability engineering
Risk assessment
Safety engineering
Six sigma
DRBFM
Fault tree analysis
[edit] Notes1.^ Langford, J. W., Logistics: Principles and Applications,
McGraw Hill, 1995, pp-488. (in paraphrase)
2.^ MIL-P-1629 - Procedures for performing a failure mode effect and
critical analysis, Department of Defense (US), 9 November 1949, http://www.assistdocs.com/search/document_details.cfm?ident_number=86479
3.^ MIL-STD-1629A - Procedures for performing a failure mode effect and
criticality analysis, Department of Defense (USA), 24 November 1980, https:/
/assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=37027
4.^ Sperber, William H. and Richard F. Stier. "Happy 50th Birthday to HACCP:
Retrospective and Prospective". FoodSafety magazine. December 2009-January
2010. pp. 42, 44-46.
5.^ Quality Associates International's History of FMEA
6.^ E. Fadlovich, Performing Failure Mode and Effect Analysis
7.^ http://www.asq.org/learn-about-quality/process-analysis-tools/overview/fmea.html
8.^ a b c Otto, Kevin; Wood, Kristin (2001). Product Design - Techniques in
Reverse Engineering and New Product Development. Prentice Hall. ISBN 0-13-
021271-7.
9.^ Kmenta, Steven; Koshuke Ishii (November 2004). "Scenario-Based Failure
Modes and Effects Analysis Using Expected Cost". Journal of Mechanical
Design 126 (6): 1027. doi:10.1115/1.1799614.
[edit] External linksFMEA and FMECA Information
FMEA Info Centre
Failure Analysis of FMEA Article
Expanded FMEA (EFMEA) Article
Scenario-Based FMEA presentation (PDF)
Difference between FMEA and Hazard Analysis | s**********8
发帖数: 25265 | 2 介有人看吗?
potential
【在 s**********8 的大作中提到】
: Failure mode and effects analysis
: From Wikipedia,
: A failure modes and effects analysis (FMEA) is a procedure in product
: development and operations management for analysis of potential failure
: modes within a system for classification by the severity and likelihood of
: the failures. A successful FMEA activity helps a team to identify potential
: failure modes based on past experience with similar products or processes,
: enabling the team to design those failures out of the system with the
: minimum of effort and resource expenditure, thereby reducing development
: time and costs. It is widely used in manufacturing industries in various
| Y*********e
发帖数: 4847 | 3 看了有包子吗
【在 s**********8 的大作中提到】
: 介有人看吗?
:
: potential
| s**********8
发帖数: 25265 | 4 ......
【在 Y*********e 的大作中提到】
: 看了有包子吗
| R**********s
发帖数: 4627 | | s**********8
发帖数: 25265 | 6 额去撞豆腐.
【在 R**********s 的大作中提到】
: 不阅
| R**********s
发帖数: 4627 | 7 我赶紧拉住椰子
【在 s**********8 的大作中提到】
: 额去撞豆腐.
| s**********8
发帖数: 25265 | 8 一起献豆腐?
【在 R**********s 的大作中提到】
: 我赶紧拉住椰子
| l*****f
发帖数: 359 | 9 老师俺看了
俺猛一看还以为讲的是FEMA哪，FEMA俺熟，FMEA第一次见
【在 s**********8 的大作中提到】
: 介有人看吗?
:
: potential
| R**********s
发帖数: 4627 | 10 不是
怕她信以为真
阻拦你撞豆腐
【在 s**********8 的大作中提到】
: 一起献豆腐?
| | | s**********8
发帖数: 25265 | 11 fema是啥? 乍一看象跳蚤
【在 l*****f 的大作中提到】
: 老师俺看了
: 俺猛一看还以为讲的是FEMA哪，FEMA俺熟，FMEA第一次见
| Y*********e
发帖数: 4847 | 12 她认为我比较硬
一起献豆腐?
【在 s**********8 的大作中提到】
: 一起献豆腐?
| Y*********e
发帖数: 4847 | 13 lol一人说一个意思
【在 R**********s 的大作中提到】
: 不是
: 怕她信以为真
: 阻拦你撞豆腐
| s**********8
发帖数: 25265 | 14 好心肠啊. 有木夹私货?
【在 R**********s 的大作中提到】
: 不是
: 怕她信以为真
: 阻拦你撞豆腐
| s**********8
发帖数: 25265 | 15 额都不好意思评论了
【在 Y*********e 的大作中提到】
: 她认为我比较硬
:
: 一起献豆腐?
| s**********8
发帖数: 25265 | 16 嫩真是好学生. 额给嫩发大红花.
【在 l*****f 的大作中提到】
: 老师俺看了
: 俺猛一看还以为讲的是FEMA哪，FEMA俺熟，FMEA第一次见
| Y*********e
发帖数: 4847 | 17 你。。。
【在 s**********8 的大作中提到】
: 额都不好意思评论了
| l*****f
发帖数: 359 | 18 Federal Emergency Management Agency
俺受过他们的training
老师要是有emergency可以call俺
【在 s**********8 的大作中提到】
: fema是啥? 乍一看象跳蚤
| s**********8
发帖数: 25265 | 19 ur number?
【在 l*****f 的大作中提到】
: Federal Emergency Management Agency
: 俺受过他们的training
: 老师要是有emergency可以call俺
| l*****f
发帖数: 359 | 20 好,俺最喜欢花花草草
【在 s**********8 的大作中提到】
: 嫩真是好学生. 额给嫩发大红花.
| | | l*****f
发帖数: 359 | 21 911 呀
【在 s**********8 的大作中提到】
: ur number?
| s**********8
发帖数: 25265 | 22 ....无语了又. 三次了都,今天
【在 l*****f 的大作中提到】
: 911 呀
| l*****f
发帖数: 359 | 23 错了
老师俺先吃饭去啦
【在 s**********8 的大作中提到】
: ....无语了又. 三次了都,今天
| s**********8
发帖数: 25265 | 24 多吃点, 好办事
【在 l*****f 的大作中提到】
: 错了
: 老师俺先吃饭去啦
|
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