FMEA vs DFMEA (What are the Differences Between Them?)

FMEA

FMEA is often used for root cause analysis to determine potential failure modes. These failure modes are the possible causes of a failure and each of them is listed and assigned a number to denote the impact of the failure.

FMEA involves the creation of a list of all failure modes, with each often being presented in a table with seven columns, as follows:

1. List of potential failure modes
2. Effect of the failure
3. Severity of the failure (on a scale of 1-10, from a minor risk to a critical risk)
4. Root causes for the failure
5. Likelihood of failure occurring (on a scale of 1-10, from extremely unlikely to inevitable)
6. Likelihood of detection (on a scale of 1-10, from extremely likely to extremely unlikely)
7. Risk priority number (RPN), created by multiplying the severity, likelihood of occurrence and likelihood of detection numbers together. The higher the RPN, the more critical the failure

FMEA is used to improve productivity, reliability and safety as well as allowing failure modes to be assessed and evaluated according to likelihood of occurring and the criticality. This allows for improved inspection and maintenance planning as well as improved security measures and troubleshooting. 

However, on the downside, FMEA is not very good at assessing multiple failures and it can be time consuming to create a full list of failure modes, which will also need frequent updating. This can prove to be a waste of resources where FMEA is not really required but can also lead to risks being underestimated if potential failure modes are not included.

Originally developed in the 1950s by the U.S. Army, FMEA has since been adopted by NASA and the aerospace industry. Since then, FMEA has gone on to be used in other safety-critical areas, including oil and gas and the automotive industry.

Because of the broad scope, FMEA is used for a wide range of processes and products, including for design updates, regulations, asset management and more.

You can find out more about FMEA here.

DFMEA

As mentioned above, DFMEA, also known as Design FMEA, stands for Design Failure Mode Effects Analysis and is used to identify potential failures in product designs during development. It was first used to prevent failures in rockets but has since found use in a range of different industries, where it is used to identify risks and take countermeasures to prevent failures from occurring.

 Similar to regular FMEA, DFMEA requires all potential failure modes to be listed along with their effects and a corresponding severity rating. Once these have been collated, DFMEA identifies root causes and potential mechanisms of failure. The higher the risk priority number, the more action is required to avoid or minimise the causes of the failure mode. All of this information is compiled on a DFMEA matrix, which provides a structure for compiling, documenting and presenting information related to technical specifications, revision dates and more. DFMEA does not need to rely on process controls to overcome any possible design failures.

The DFMEA process can be broken down into ten steps, as follows:

1. Design Review: Assess the part in relation to the product and other parts to determine its expected function
2. Identify Potential Failure Modes: Identify and list the ways in which the part could fail
3. Identify Potential Failure Effects: List the effects of the identified failure modes
4. Identify Potential Causes of Failure: List the design elements that contribute to the potential failures
5. Assign a Severity Rating: Determine a severity rating from 1-10, with one equalling low risk and ten equalling a high level of severity should the failure occur
6. Assign an Occurrence Rating: Determine a rating for the chance of the failure occurring from 1-10, with one being very unlikely and ten being extremely likely or inevitable
7. Assign a Detection Rating: Assign a detection ranking between 1 and 10, with one being a failure that is easy to detect and ten being one that is extremely difficult to detect
8. Calculate a Risk Priority Number (RPN): Multiply the severity rating by the occurrence rating and the detection rating to create an RPN of between 1 and 1,000, with one being low risk and one thousand being a very high risk
9. Create an Action Plan: Develop a plan of action based on the RPN to decrease the chance and the impact of any potential failures
10. Recalculate the Risk Priority Number: Recalculate the RPN to measure improvements once failure control measures have been put into action

Defect Detection Costs and DFMEA

One of the major advantages of DFMEA is cost-saving. It is far less expensive and time-consuming to correct a defect earlier on in the product lifecycle, with the design stage being the easiest and cheapest at which to correct any potential failures.

The cost of correcting any issues at the design stage involves the time taken for a redesign, but moving forward to the production stage and the cost of correcting a defect rises dramatically. At this point it can involve shutting down production, re-engineering, retesting and restarting production – not to mention the potential cost of wasted materials.

The cost of defect correction increases even further once a product reaches the market, as recalls, product replacement and repair, as well as damage to your reputation all come into play.

FMEA and DFMEA Applications

There is a lot of cross-over between the applications for FMEA and DFMEA, although DFMEA allows any failures to be detected and corrected early on in the product or process lifecycle, reducing costs.

As a result, DFMEA is particularly useful for areas where risk reduction and failure prevention are crucial.

However, both DFMEA and FMEA are used in industries including:

• Healthcare
• Manufacturing
• Software Development
• Business Process Management
• Service Industries
• Regulated Industries such as Oil and Gas, Aerospace, Automotive and Astrospace

What is the difference between a FMEA and DFMEA?

DFMEA is a type of FMEA, meaning that the only real difference is that DFMEA is solely related to the design stage, whereas FMEA covers a broader range of potential failures, including production and in-service.

DFMEA tends to be used mainly for products, while FMEA can also be used for processes, procedures and services.

The final major difference is that DFMEA tends to be much cheaper than performing FMEA at a later stage to correct a failure.

Conclusion

Given that DFMEA is a type of FMEA, there are a lot of similarities between them. Each method uses a series of steps to list and then assess failure modes for severity, chance of occurrence and likelihood of detection in order to create a risk priority number.

The difference between the two is that FMEA is used across a range of products, processes and services from design to production and in-service fault detection and mitigation, while DFMEA is only used during the design stage, and mainly for product design.