Introduction
Failure Mode and Effects Analysis (FMEA) is a methodology, an approach, and a systematic tool in one. It aims to identify potential risks and failures proactively ("what
can go wrong"), the cause of the failures, and the effects or consequences of them. In addition FMEA ranks all potential failures based on severity, occurrence and detectability. In essence the major objective
of FMEA is to improve the relevant process, product or system for what the FMEA is being conducted. The benefits of FMEA:
- It focuses on prevention, so it eliminates early design and process related concerns.
- Improves design and processes.
- Contributes to design and manufacture reliable products, which increases customer satisfaction.
- Saves money for the company (increases Cost of Good Quality, but decreases Cost of Poor Quality significantly).
FMEA also focuses on taking actions to prevent / detect failures, and follows up the results of these actions, and how they decrease the impact of failures, so it is a living
document, continuously updated by FMEA specialists.
The basic principles of FMEA were developed by engineers of the US Military in the 1940s, and it was further improved by the automotive and aerospace industries in the past
decades. Various guidelines, manuals and standards exist for conducting FMEA, e.g. the
AIAG FMEA manual, IEC 60812
international standard, or the SAE ARP 5580.
Source: qMindset.com; AIAG FMEA Manual
TEST ADVERTISEMENT (for temporary testing purposes, source: presse.porsche.de)
Key Features
Being a living document, FMEA is not just a tool of proactive risk analysis, but a documented frame of historical information about the product, process or system.
Nowadays we differentiate various FMEA types, such as:
- Design Failure Mode and Effects Analysis (DFMEA) (used to identify, analyse and manage design related risks).
- Process Failure Mode and Effects Analysis (PFMEA) (used to identify, analyse and manage process related risks).
- System FMEA (focuses on the risks of various systems, sub-systems, and the interaction between these sub-systems).
- Business Process FMEA (manages risk and failure related to business processes).
- Software FMEA (analyses software risks, and how the software is able to handle hardware defects).
Conducting FMEA provides several benefits during product design and process development. FMEA features and benefits:
- Preventive and systematic.
- Support of product and process development.
- Creative teamwork (more eyes see more).
- Increases the chance to catch potential failures up-front (cost effective, as prevents failure costs in later project phases).
- Improves product safety.
- Useful tool (and basis) for Control Plan creation
The analysis concentrates on three attributes of the FMEA, which are:
- Severity (S), which reflects the seriousness of the failure effect (impact) on the sub-system, system, or customer.
- Occurrence (O), what shows the probability of the cause or failure mechanism that may occur.
- Detection (D) that assesses the potential / ability to detect the failure.
Creating and sustaining a valid and effective FMEA is not possible without knowledge, and an experienced team. The following points cover the creation of a process FMEA:
- Choose the right participants / team members with relevant knowledge and experience of the given process or product.
- Establish the cross-functional team.
- Define the scope (e.g. process FMEA for a manufacturing process).
- Define the process steps, and all functions, based on the process concept, which will be the focus of the analysis (e.g. mounting, screwing, gluing, welding, etc. in case of a process FMEA).
- Identify all possible failure modes, which means the way failures can happen (e.g. insufficient screwing).
We can distinguish five basic failure mode categories: complete failure (no function), function out of specification (improper function), partial failure (failure of sub-function), intermittent failure
(failure that is not always active), unintended function (unexpected behaviour of product, component, or process).
- Identify the effects or impact of each failure mode. This section reflects what the customer notices, experiences (e.g. screw gets loose and the back-plate falls off).
- Rate the effect of the failure from severity point of view (S range goes from 1 to 10, number 10 means the highest severity). In addition, determine if the given effect is functional relevant, safety
relevant, or it correlates with any governmental regulation, and mark it in the FMEA (e.g. S – safety relevant critical
characteristic, F – functional relevant critical characteristic, G – governmental regulated critical characteristic).
- Determine the potential root causes for each failure mode (e.g. insufficient screwing torque).
- Enlist all actually planned or existing process controls, which prevent the occurrence of the failure.
- Rate all root causes from occurrence point of view, which means how probable the failure is (O range goes from 1 to 10, number 10 means the highest probability).
- Enlist all actually planned or existing process controls, which detect the occurrence of the failure.
- Rate all process controls from detection point of view, which means how detectable the failure is (D range goes from 1 to 10, number 1 means the highest probability, that a failure will be detected).
- Determine the overall risk of each failure, by calculating the Risk Priority Number (RPN), which is the product of Severity (S), Occurrence (O) and Detection (D) numbers (RPN = S x O x D). RPN goes from
1 to 1000, where 1 means the lowest risk.
- To decrease Occurrence and Detection numbers, you can take actions, based on the work of the cross-functional team. These actions can decrease the probability of the failure, and increase the detection
rate.
- After the definition of actions, modify the Occurrence and Detection rates accordingly, and re-calculate the modified Risk Priority Number (RPN).
The FMEA chain (Source: qMindset.com)
Conducting an FMEA is not only an issue of new product introduction, but it should cover all product / process / system changes. FMEA is also updated if corrective actions are
verified and implemented as an outcome of an
8D process.
For administrative reasons, and better tracking, the FMEA spreadsheet needs to contain header information, such as:
- FMEA identification number.
- Relevant line / product / part number / customer.
- Date of creation / date of last review or update.
- Affected location / site / plant
- Revision history (summary about what was modified and when).
- Marking of special characteristics (e.g. governmental, functional, safety relevant).
- Members of the FMEA team.
- Sign-off by quality / design / engineering, etc.
FMEA is a crucial point of quality planning, thus it is in close connection to the
Advanced Product Quality Planning
(APQP) framework. Both DFMEA and PFMEA have their place in the APQP timeline. Conducting DFMEA starts in the planning phase, and ends with the design freeze, having an accepted prototype build. PFMEA is also
initiated in the planning phase, but it finishes later in the product and process validation phase, by having a reliable manufacturing process and a pilot build.
The place of FMEA in the APQP framework (Source: AIAG APQP Manual)
Source: qMindset.com; AIAG FMEA Manual; AIAG APQP Manual
Hints
To conduct a proper FMEA creation, or update, the cross functional team is necessary, including engineering and design, quality experts, process and product engineering,
etc. To find as many potential failure modes and root causes as you can, the barnstorming of the team is essential.
Common mistakes of conducting an FMEA:
- Mixing failure modes with causes and effects.
- Missing out potential failures.
- Improper ranking of Severity, Occurrence or Detection (being too optimistic).
- Taking inefficient actions, what do not reduce Occurrence and Detection ranking in the expected way.
- Focusing only on high RPN numbers, instead of focusing on failures with high Severity (S), or high criticality (S x O).
You should not only focus on failure modes and root causes with the highest RPN numbers, but also on those ones, that have very high Severity and Occurrence numbers (e.g. S > 8
and O > 2 should be covered with an effective Detection with D < 2). The product of S and O numbers is criticality, which is the major source to define when to take action. The consideration of risk classes
is variable depending on the company, but it is important to have rules about how to define detection related actions based on criticality (S x O). The following chart illustrates and example, how criticality
can correlate to detection.
The FMEA relation of Criticality and Detection (Source: qMindset.com)
DFMEA is the basis of PFMEA, so conducting a PFMEA is not possible without having DFMEA. This also means, that modifying your design and your DFMEA must be reflected in PFMEA
as well. As your design change can influence your manufacturability, it might happen, that you need to change your process parameters, or the whole process itself.
The following chart illustrates the place of FMEA in the quality planning process:
FMEA in the Product Engineering Process (Source: qMindset.com)
Source: qMindset.com
Summary
- FMEA stands for Failure Mode and Effects Analysis.
- FMEA aims to proactively identify potential failure modes, their causes and effects.
- Additionally, FMEA focuses on the actions that reduce risks, by the prevention and detection of the failures.
- RPN stands for Risk Priority Number, and it is the product of Severity (S), Occurrence (O) and Detection (D).
- FMEA methodology was developed by the U.S. Military, and was further improved by the automotive and aerospace industries.
Source: qMindset.com; AIAG FMEA Manual
