Failure mode and effects analysis (FMEA) was first developed by the U.S. military in the 1940s and is now widely used in industries including aerospace and electronics. The role of FMEA is to identify potential problems that may occur in during manufacturing, assembly or design as well as determining the subsequent effect of failure. Risk priority numbers (RPN) are calculated to determine the likelihood of failure, the severity of any failure and the effect of corrective actions. RPNs are calculated by multiplying three variables; severity of the failure (S), the occurrence of the failure (O), and the likelihood of the failure being detected (D). This multiplication creates the failure mode criticality.
The data is typically used in design and control, particularly for the launch of a new product or adding new features or adapting an existing product. If a product or process doesn’t work as intended, FMEA can help show the cause of any problems.
Failures modes and effects analysis is a step-by-step approach that splits the cause of a failure (or potential failure) from the impact of the failure. FMEA allows for necessary actions to be taken to solve any issues, starting with the highest priority ones.
The different types of FMEA include design FMEA, process FMEA and concept FMEA, which each have their own applications and advantages.
The general benefits of FMEA include prevention planning, cost reductions, ability to identify change requirements, increased throughput and decreased waste. FMEA also offers decreased warranty costs and a reduction in non-value added operations.
These benefits are added to by additional benefits from concept, design and process-based FMEA, as follows:
1. Concept FMEA
Concept FMEA helps to select the best concept alternatives and decide upon changes to design specifications. It also identifies potential failure modes caused by interactions within the concept and allows for the potential effects of conceptual failures to be considered. In addition, concept FMEA identifies system level testing requirements and helps ascertain whether hardware redundancy is required within the design proposal.
2. Design FMEA
Design FMEA helps to objectively evaluate design requirements and alternatives. This aids in the initial design for manufacturing and assembly of parts and allows potential failure modes from the design process to be considered. These failure modes are ranked so that they can be addressed according to their impact and provides additional information to plan test programmes. Risk reduction actions can be stored and tracked as an aid to investigating later field concerns or design developments.
3. Process FMEA
Process FMEA identifies potential process failures, their potential effect on customers and identifies where controls or monitoring can be applied. By ranking the failure modes apriority system can be established for corrective actions. Process FMEA also documents the results of the manufacturing or assembly process to identify process deficiencies. As well as identifying any operator safety concerns, this form of FMEA shows confirmed critical or significant characteristics and feeds information on any changes required.
For all of the benefits of the various types of FMEA, there are also a few difficulties that need to be taken into consideration. These disadvantages include:
1. Tendency Towards High Severity Ratings
FMEA tends to show a bias towards high severity ratings regardless of the associated chances of occurrence and detection. For example, the severity of an exploding machine could be ranked at severity 10 even though the chances of this happening and the likelihood of detection are both rated at 1. However, due to the high severity rating, no improvement in FMEA is possible as severity ratings are difficult to reduce.
While severe problems should be assed to an FMEA control sheet, a decision needs to be made as to when a potential problem is so minimal that it doesn’t need listing. Instead, these minor issues can just be dealt with as they arise, preventing such needless FMEA procedures and the associated meetings from getting in the way of actual work. Successful FMEA requires a detailed analysis of processes and procedures, so can be time-consuming. For this reason, the scope of an FMEA procedure needs to be clearly defined.
3. Assessment Only
FMEA only provides assessments, it doesn’t eliminate the problems that it uncovers. There is still a requirement to solve any problems.
4. Reliant on Team Experience
The more experienced your team, the better the FMEA will be. Not only will your team be better equipped to locate possible failure modes, but they will also be more effective at solving and mitigating against any problems.
5. Requires Design Stage FMEA
Skipping FMEA at the design stage will weaken the effectiveness of the whole procedure at later stages. Effective FMEA requires each step of a process, procedure or service to be examined.
Customers expect products that are safe, efficient and functional, and FMEA can help meet these demands by delivering high-quality goods and services. FMEA can be adapted to a wide range of industries and applications, from aerospace to healthcare and baking to software. For example, hospitals can perform FMEA on their devices and banks can use FMEA to find flaws in ATM machines.
FMEA can improve designs for products to deliver safer, better quality and more reliable products as well as reducing the associated costs for product development. It also provides information that can be used to show products meet the highest quality and safety standards like Six Sigma, PSM and ISO 9001.
These benefits mean that FMEA has found applications right across industry and manufacturing, including oil and gas, defence, automotive and more.
Failure modes, effects and criticality analysis (FMECA) builds upon the FMEA process by not only identifying potential failure modes but also investigating and isolating any potential failure through a series of actions.
Failures are assigned a severity level as with FMEA, but FMECA goes into more detail to provide more accurate results, along with ranking those errors with the highest criticality number. FMECA requires the application of FMEA before the extra criticality analysis actions can be taken. The criticality analysis charts the probability of failure modes against the impact of the consequences, allowing you to focus on the most critical aspects.
As with FMEA, FMECA can be used to help fulfil quality and safety requirements.
FMECA provides many of the same benefits as FMEA, including for prevention planning, identifying change requirements, reducing costs and waste, increasing throughput and reducing any non-value added operations.
In addition, FMECA has the advantage of being more comprehensive than FMEA by establishing relationships between failure causes and effects and the criticality of corrective actions.
As with FMEA, FMECA can help improve the design of products and processes to provide improved reliability, safety, quality, and the resulting customer satisfaction.
As with FMEA, FMECA comes with its own difficulties that need to be taken into account. These include the amount of labour required, the potential for trivial cases to be considered as part of the process, and the difficulty in assessing multiple-failure or cross-system effects. FMECA also doesn’t typically consider software or human interaction implications.
FMECA also has a tendency to deliver an optimistic estimate of reliability, meaning that it is best used alongside other analytical tools for developing reliability estimates.
Just like FMEA, the applications for FMECA cover a wide range of industries and manufacturing procedures.
FMECA can be used any time higher quality products with an increased reliability and safety are desired. It can also reduce costs and even be used to help avoid lawsuits.
As with FMEA, FMECA can also help with meeting quality and safety standards, including Six Sigma, PSM and ISO 9001.
These methods are used for design, manufacture, development and other business-critical applications for industries ranging from aerospace and construction to healthcare, software, and beyond.
Many people believe FMEA and FMECA to be interchangeable and pretty much the same thing, but there is a difference between the two techniques. FMEA originally lacked the severity, occurrence and detection rankings and the criticality matrix of FMECA was necessary for FMEA risks to be prioritised. As the templates for FMEA developed, FMECA was less necessary. The criticality analysis aspect of FMECA is performed post-FMEA.
Where FMEA only offers qualitative information, FMECA offers both qualitative and quantitative information, allowing users to measure a level of criticality to failure modes and order them according to importance.
FMECA is usually conducted either with a top-down or a bottom-up approach. The top-down approach is typically used in the early design phase as a function-orientated procedure to examine how system functions may fail. The bottom-up approach is typically taken when the system concept has been decided. This involves the study of each component from the lowest level up. In both cases, a criticality matrix is created that can help determine the critical items and provide recommendations based on the analysis.
Generally-speaking, a quantitative approach should be taken when actual component data is available and a qualitative approach should be taken when there is either no component data or only generic component data available.
FMEA is a part of FMECA, so the question here is not so much when each should be used as when criticality analysis is required as an additional step to FMEA.
FMEA is used to establish, via failure mode analysis, the effect of failures and can be undertaken at various stages of a process to create conceptual, functional, design and process FMEA.
As a result, FMEA can be used for:
- Designing or redesigning a process, product or service following the deployment of quality functions
- Developing more features for an existing product
- Creating or updating control plans for a process, product or service
- Analysing failures within an existing process, product or service
FMEA becomes FMECA with the addition of critical analysis, which allows the FMEA team to identify those failure points that are critical along with the probability that it will occur.
FMEA was invented by the U.S. military in the 1940s and continues to be used by them today under the MIL STD-1629A military standard. Since then FMEA has spread across a wide range of industries to assess services, products and processes, from manufacturing to software design and healthcare procedures.
You can find out more about FMEA in this related FAQ, but put simply, FMECA is FMEA with the addition of a criticality analysis step at the end.
Improving safety, reducing costs and improving throughput, FMEA and FMECA are both useful for proof of quality and standards procedures, although FMECA also has the additional advantage of establishing relationships between failure causes and effects and the criticality of corrective actions.