FMEA

FMEA ( English Failure Mode and Effects Analysis , German Failure mode and effect analysis or short impact analysis ) and FMECA (Engl. Failure Mode and Effects and Criticality Analysis ) are analytical methods of reliability engineering . Possible product defects are evaluated according to their importance for the customer, their probability of occurrence and their probability of detection, each with a key figure.

As part of quality management and safety management , the FMEA is used preventively to avoid errors and increase technical reliability. The FMEA is used in particular in the design and development phase of new products or processes . Widely used, this method is in the automotive industry and the aviation and aerospace , but also in other industries , a properly conducted FMEA is often required.

Base

FMEA aims to avoid errors from the outset instead of discovering and correcting them afterwards. Potential causes of errors should be identified and evaluated as early as the design phase. This avoids control and error costs in production or even for the customer. The knowledge gained in this way also avoids the repetition of design deficiencies in new products and processes.

The FMEA methodology should already be applied in the early phase of product development (planning and development) within the product life cycle , since cost / benefit optimization in the development phase is most economical (preventive error avoidance). The later an error is discovered, the more difficult and costly it will be to correct it.

species

The FMEA can be divided into several types:

Design FMEA (D-FMEA): The design or construction FMEA (also K-FMEA) is used in development and construction to assess the suitability of a product for production and assembly as early as possible. The consideration includes systematic errors during the construction phase.

System FMEA (S-FMEA): The system FMEA examines the interaction of subsystems in a superordinate system network or the interaction of several components in a complex system. It aims to identify potential weak points, especially at the interfaces, that could arise from the interaction of the individual components or the interaction of the own system with the environment. The consideration includes random and systematic errors during operation.

Hardware FMEA: The aim of a hardware FMEA is to analyze and evaluate risks in the area of hardware and electronics and to take measures to remedy them.

Software FMEA: A software FMEA performs the same task for generated program code.

Process FMEA: The process FMEA (also P-FMEA) can be based on the results of the construction FMEA, but can also be carried out in isolation. It deals with possible weak points in the process aimed at increasing quality.

The VDA 2007 combined the system FMEA and the HW / SW / construction FMEA to form the so-called product FMEA , as the system to be considered can usually not be clearly resolved.

The system FMEA product is used within the development process. It is your job, on the one hand, to examine the product to ensure that the functions specified in the specification are fulfilled , and, on the other hand, to collect and evaluate possible errors that lead to non-compliance with the requirements. Suitable measures to avoid or detect potential defects must be planned for all risky parts of a product. The system FMEA at component level corresponds to the previous definition of the construction FMEA. It is used to analyze all component features that are necessary to fulfill the required component function.

The system FMEA process is still used within the production planning process. It is logically based on the results of the subordinate FMEA. An error in the system FMEA product, the cause of which lies in the manufacturing process, is consequently adopted as an error in the process FMEA. The task of the System-FMEA Process is to examine the entire manufacturing process of a product for its suitability for manufacturing the product. Suitable measures to prevent or detect any errors that may occur during the manufacture of the product must be planned.

application

During the application, a team of employees from various corporate functions (interdisciplinary team) is first formed. In particular, construction, development, testing, production planning, production execution, quality management etc. are to be included. The analysis process itself is then formalized with the help of forms (e.g. QS-9000, VDA form, AIAG form, ...) or corresponding software (VDA 4.2) carried out.

The FMEA contains

a limitation of the system under consideration,
a structuring of the system under consideration,
Definitions of functions of structural elements,
an analysis of potential causes of errors, types of errors and consequences of errors that are derived directly (e.g. using the W questions ) from the functions of the structural elements,
a risk assessment,
Suggested measures or solutions for prioritized risks
tracking of agreed prevention and detection measures and
a residual risk assessment or assessment.

Potential errors are analyzed by locating the location of the error, determining the type of error, describing the consequence of the error and then determining the cause of the error. A so-called cause-effect diagram can be created to determine the possible causes of errors . Corrective measures for avoidance and / or detection should be defined and implemented for each identified possible cause of error.

The ratios B , A and E (in English SOD ) for B EANING (the error sequence, engl. Severity S ), A uftretenswahrscheinlichkeit (the error cause, engl. Occurrence O ) and E ntdeckungswahrscheinlichkeit (the fault or its cause; possibly also the Consequence; Detection D ) are a basis for risk assessment. The key figures are integer numerical values between 1 and 10 and are assigned with the help of evaluation catalogs.

With the calculation of the risk priority number ( RPN ) an attempt is made to establish a ranking of the risks. The RPN is created by multiplying the B, A and E evaluation numbers ( ) and can accordingly assume values between 1 and 1000. The requirement should exist that the RPZ, at least in comparison with other RPN of the same FMEA, allows a statement in the sense of better / worse . However, this is generally not met according to DIN EN 60812. ${\ displaystyle RPZ = B \ cdot A \ cdot E}$

The goal of the RPZ to assess the significance and the rank of an error in order to derive priorities for the measures to be taken is questioned again and again . There have been attempts to work with the parameter ( ) in addition or as an alternative . With Design Review Based on Failure Mode (DRBFM, failure detection supported construction change), the FMEA system used at Toyota, the definition of key figures is omitted entirely. Measures are only assessed there by experts or determined as a result of the team discussion. ${\ displaystyle B \ cdot A}$

Goals of the FMEA

The goals of the FMEA are derived from the company goals. Increased quality and risk demands of customers have an impact, as does the required cost optimization of products and processes. The corporate goals are broken down into quality and risk management, i.e. made more concrete, then they are action goals.

Achieve corporate goals
Proof of safety
Proof of product / system or plant performance or availability
Increasing the functional safety and reliability of products and processes
Proof of discharge in the event of product liability
Targeted communication in internal and external customer and supplier relationships
Build a knowledge base
- Basic FMEA
  - Variants - Project FMEA
Create an understanding of the functional relationships between parts, assemblies and components as well as processes and sub-process steps
Save costs by reducing unplanned start-up costs, reducing rejects in production, avoiding 0 km complaints and field failures and the associated costs

activities

A distinction is made between preventive measures and detection measures. Avoidance measures serve to justify the rating number for the probability of occurrence (A) and detection measures to justify the rating number for the probability of detection (E). In case of doubt, avoidance should be preferred over detection.

Measures at the current status (initial status) are usually documented without a responsible person or deadline. The RPN for the actual status is calculated using the evaluation numbers for B, A and E.

Additional measures are aimed at

the A to reduce uftretenswahrscheinlichkeit an error cause (z. B. improved by the incorporation of components).
the E ntdeckenswahrscheinlichkeit for a potential error cause to increase by example. additional tests are provided.

If changes are made to the product or process, a new risk assessment is required for the area affected by the change. An "improved component" can e.g. B. in addition to positive aspects have a higher weight or a higher power consumption.

For pragmatic reasons, the detection measure will usually not discover the cause of the error, but rather the error or the result of the error. However, the documentation usually takes place with the cause of the error.

If a continuous improvement process is to be supported, the measures are grouped in measure statuses, each with their own A and E evaluation numbers and thus their own RPN.

In the field of the automotive industry, the action statuses are also categorized in construction FMEA in order to be able to address the issues of development, field and service in the event of the causes of errors. Each category has its own RPZ.

The risk assessment in the current FMEA no longer takes place solely through the RPZ already mentioned, but rather according to the following sequence:

Highest priorities have high meanings (10), after which the product is made of B EANING and A uftretenswahrscheinlichkeit considered (B * A), this is also called criticality or technical risk referred (Considerations include the valuation numbers stored catalogs, A = x is a Range and no fixed ppm number for the probability of occurrence of the error).

Only then does the RPZ intervene to prioritize the remaining points.

rating

The evaluation is carried out by interdisciplinary teams, each awarding points from “10” to “1”. It is always graded from the higher rating to the lower rating.

B EANING or S chwere the error sequence is evaluated from the perspective of the customer (high = "10" to low = "1").
A uftretenswahrscheinlichkeit the cause (high = "10" to low = "1")
E ntdeckenswahrscheinlichkeit the cause or the error in the process, before delivery to the customer (low = "10" to high = "1")

The customer can be both the end customer and an intermediate customer (e.g. internal company) who requests the FMEA. R isiko- P rioritäts- Z ahl (RPN; also RPN) can be used to rank the agreement of countermeasures in the development process. The RPZ alone is not suitable for assessing risk potential. An RPZ of 120, for example, can have been created in different ways, such as B. from B × A × E = 10 × 3 × 4 or from 5 × 8 × 3. A meaning of B = 10 and a rather moderate discovery of E = 4 is less acceptable than an error sequence rated B = 5 which occurs very frequently (A = 8) but is well discovered (E = 3).

An assessment of the absolute risk potential can not be derived from the factors .

Various companies have defined their own catalogs based on the standards for assessing risks and criteria for taking measures to reduce risk.

After the initial assessment and the completed measures, a new risk assessment is carried out: A new RPN is determined to check whether the planned measures promise a satisfactory result (the significance of the consequences of the error remains unchanged). If the result does not yet meet the quality requirements of the customer, further avoidance or detection measures must be taken and / or solutions must be developed.

VDA Volumes 4, Parts 2 and 3 recommend a systematic approach in detail.

criticism

Since 2003 it has been proven that the classic construction of risk priority numbers contains systematic weaknesses, in particular:

The multiplication of the ordinally scaled features B, A and E is strictly mathematically undefined.
There is no guarantee that the same RPN will be assigned to similar risks.
There are risks that are assigned the same RPN but are not equally acceptable.

It is also known how these problems can be resolved and it has also been shown quantitatively that RPN treats risks in the same way, although they differ by several orders of magnitude.

As a result, these design weaknesses were also named in DIN EN 60812 in 2006. The fundamental work to explain and remedy the weaknesses was awarded the Walter Masing Prize in 2007 by the German Society for Quality . The resulting general requirements for methods for risk analysis based on RPZ were specified in DIN VDE V 0831-101.

These findings have led to adjustments to the RPZ method in some industries; a new method based on this was introduced in railway signaling technology with DIN VDE V 0831-103.

For the North American and European automotive industry, there will be significant changes from the second half of 2019 as part of the FMEA harmonization of AIAG and VDA. Among other things, the calculation of the RPN is replaced by the new key figure task prioritization. This makes no statement about the existing risk, but indicates for each combination of B, A and E how urgently additional measures are necessary. In addition, the form will be expanded by additional columns and a new 1st step for FMEA creation (scope of consideration) will be introduced.

Historical

For the first time, a description of the FMECA method was published as the United States Military Procedure . The fields of application of the FMEA / FMECA have expanded over time. Originally located in the military sector, the FMEA found its way into the automotive industry after its spread in the aerospace industry. The widespread use of FMEA in the automotive industry was initiated by Ford after sensational problems with the Ford Pinto model in the 1970s . Since the FMEA is based on a universal method model, it is also used in other areas in which work is carried out systematically, e.g. B. Medical technology, food industry (as hazard analysis and critical control points , abbreviated to HACCP), plant construction, software development.

In the 1970s, the three largest US automobile companies GM , Ford and Chrysler confronted their suppliers with individual FMEA guidelines. One of them had z. B. only five evaluation numbers for B, A and E. At the initiative of the suppliers, a standardization in the form of the QS-9000-FMEA was achieved in the early 1980s; the Big Three (Ford, GM and Chrysler) took the FMEA method description from Ford as a basis and added only a few indispensable additions in the form of attachments, e.g. B. each with its own symbols for the classification. In the years that followed, FMEA was introduced across the board in the supplier industry. In 1996 the Association of the Automotive Industry (VDA) published an improved FMEA system. In the third edition of the QS-9000-FMEA method description available since 2002, some elements of the VDA approach were adopted. In 1997, Toyota first described a change-focused FMEA, now known as the DRBFM methodology . In March 2007 the "VDA FMEA 2nd edition" went to print. After the QS-9000 standards are no longer up-to-date, the AIAG was chosen as the publisher of the now available "AIAG-FMEA 4th edition" (June 2008).

Norms and standards

There are various norms and standards for the FMEA depending on the application context. A general, context-unspecific standardization was carried out in 1980 by DIN 25448 under the keyword “failure effect analysis”. This standard was updated in 2006 by DIN EN 60812 under the heading "Defect state type and effects analysis". There are also numerous context-specific standardizations, the following is a small selection:

Design Review Based on Failure Mode (DRBFM): The DRBFM was developed by Toyota as a change-focused FMEA method. The DRBFM should remove the separation between development and quality processes and integrate the development engineer more directly into the quality process.
Hazard analysis and critical control points (HACCP)

literature

DIN EN 60812: Analysis techniques for the functionality of systems - Methods for the type and effects of faults analysis (FMEA) , November 2006
DIN VDE V 0831-101: Electrical railway signaling systems - Part 101: Semi-quantitative methods for risk analysis of technical functions in railway signaling technology , May 2011
DIN VDE V 0831-103: Electrical railway signal systems - Part 103: Determination of safety requirements for technical functions in railway signal technology . November 2014
DGQ : Volume 13–11 FMEA - Failure Mode and Effects Analysis. 3. Edition. 2004, ISBN 3-410-32962-5 .
Otto Eberhardt: Risk assessment with FMEA. 2012, ISBN 978-3-8169-3128-7 .
Roland Mathe: FMEA for supply chain management. Recognize process risks at an early stage and effectively avoid them with Matrix FMEA. Symposion Publishing GmbH, Düsseldorf 2012, ISBN 978-3-86329-448-9 .
Dieter H. Müller, Thorsten Tietjen: FMEA practice. 2nd Edition. 2003, ISBN 3-446-22322-3 .
VDA : VDA Volume 4 Quality assurance before series production - System FMEA. 1st edition. 1996, ISSN 0943-9412 (replaced by 2nd edition 2006)
VDA: VDA volume 4 Quality assurance before series production - product and process FMEA. 2nd Edition. 2006 (loose-leaf collection)
Martin Werdich: FMEA - introduction and moderation. 2nd Edition. Vieweg & Teubner 2012, ISBN 978-3-8348-1787-7 .

Individual evidence

↑ QS-9000
↑ Basics of failure mode and effects analysis. In: quality and reliability . Retrieved December 25, 2014 .
↑ FMEA - Failure Mode and Effects Analysis. (PDF) German Society for Quality , 2012, accessed on December 25, 2014 .
↑ Björn Richerzhagen: Process FMEA. In: Blog. MINAUTICS, accessed April 17, 2020 .
↑ Thorsten Tietjen, Dieter H. Müller: FMEA practice. Edition 2. Hanser Verlag, 2003, ISBN 3-446-22322-3 .
↑ FMEA - Failure Mode and Effects Analysis - Quality Services & Wissen GmbH. Retrieved May 18, 2017 .
^ J. Bowles: An Assessment of RPN Prioritization in a Failure Modes Effects and Criticality Analysis. In: Proc. RAMS2003, Tampa, January 2003.
^ J. Braband: Improving the Risk Priority Number Concept. In: Journal of System Safety. 3, 2003, pp. 21-23.
↑ S. Kmenta, K. Ishii: Scenario-based Failure Modes and Effects Analysis using Expected cost. In: ASME Journal of Mechanical Design. Vol. 126, No. 6, Issue MD-04-1027, 2005, pp. 1027-1035.
↑ J. Braband: Limited Risk. In: quality and reliability. 53 (2), 2008, pp. 28-33.
^ Walter Masing Prize Winner 2007 , German Society for Quality Assurance.
↑ VDA yellow tape accessed on July 15, 2018
↑ MIL-P-1629 - Procedures for Performing a Failure Mode, Effects and Criticality Analysis. November 9, 1949.
^ Ford Fuel System Recalls .

[1] QS-9000

[2] Basics of failure mode and effects analysis. In: quality and reliability . Retrieved December 25, 2014 .

[3] FMEA - Failure Mode and Effects Analysis. (PDF) German Society for Quality , 2012, accessed on December 25, 2014 .

[4] Björn Richerzhagen: Process FMEA. In: Blog. MINAUTICS, accessed April 17, 2020 .

[5] Thorsten Tietjen, Dieter H. Müller: FMEA practice. Edition 2. Hanser Verlag, 2003, ISBN 3-446-22322-3 .

[6] FMEA - Failure Mode and Effects Analysis - Quality Services & Wissen GmbH. Retrieved May 18, 2017 .

[Bowles-7] J. Bowles: An Assessment of RPN Prioritization in a Failure Modes Effects and Criticality Analysis. In: Proc. RAMS2003, Tampa, January 2003.

[Braband-8] J. Braband: Improving the Risk Priority Number Concept. In: Journal of System Safety. 3, 2003, pp. 21-23.

[Kmenta-9] S. Kmenta, K. Ishii: Scenario-based Failure Modes and Effects Analysis using Expected cost. In: ASME Journal of Mechanical Design. Vol. 126, No. 6, Issue MD-04-1027, 2005, pp. 1027-1035.

[QZ-10] J. Braband: Limited Risk. In: quality and reliability. 53 (2), 2008, pp. 28-33.

[DGQ2007-11] Walter Masing Prize Winner 2007 , German Society for Quality Assurance.

[12] VDA yellow tape accessed on July 15, 2018

[13] MIL-P-1629 - Procedures for Performing a Failure Mode, Effects and Criticality Analysis. November 9, 1949.

[14] Ford Fuel System Recalls .