FMEA In Six Sigma: RPN, Tools and FMEA Examples

FMEA is an acronym for Failure Mode Effects Analysis. It is also known as failure modes, effects and criticality analysis (FMECA) or potential failure modes and effects analysis. FMEA in six sigma is useful in identifying possible failures and to come up with a plan to remedy it. 

Six Sigma is a management tool used for quality improvement. Consequently, FMEA is used as a six-sigma tool to detect and eliminate, as much as possible, likely failures in a product, service, process or design. FEMA was initially used by the US military in the 1940s and was later deployed by the nautical, automotive and aerospace industries. Today, many other industries also maintain FMEA principles.

Furthermore, FMEA helps managers to thoroughly understand the organization’s processes. It helps to identify threats and develop actions to counteract them. FMEA establishes a multidisciplinary team, thereby, encouraging the transfer of skills.

This article covers the concept of FMEA in six sigma with regards to these areas:

• RPN in six sigma
• Examples of FMEA in six sigma
• Six Sigma tools

FMEA in Six Sigma

Six Sigma helps to reduce and eliminate errors that occur in organizational processes. These errors or defects can have a negative effect on the customer’s experience. Likewise, FMEA in six sigma enables project teams to identify the likelihood of failure occurring in a process, product or service. It also evaluates the extent to which these failures can affect the customer. Consequently, FMEA helps to determine probable causes of failures and how they can be fixed.

FMEA is implemented during the Analyse stage of the six sigma DMAIC cycle to identify products that are susceptible to failure. Also, it can be employed during the Design phase to ascertain processes that require improvement.

More so, FMEA can be employed to design or design a process, product or service.

There are two types of FMEA in six sigma. They are Design FMEA (DFMEA) and Process FMEA (PFMEA). Design FMEA is used to identify and analyse the chances of failure in a product or hardware design. On the other hand, Process FMEA is used to identify and analyse the chances of risk in a particular design or process. Hence, where a process is already established and only requires upgrading or improvements, the project team may not set up FMEA afresh.

When setting up a project team for FMEA, organizations should seek to combine the best skills. This will help to achieve optimum results. They could include internal and/ or external experts. Nevertheless, the team should comprise of members from every department affected by the process under review.

Through a multidisciplinary team, FMEA aids in the transfer of skills and knowledge among team members. Therefore, every member of the team is able to understand the process thoroughly. In addition, they are able to develop a good understanding of all the interrelated parts of the process.

Generally, the project team can implement FMEA in a series of steps. First of all, they compile a list of probable failures that could occur during the process. Next, they measure the effect that each of the failures will have on the process. Afterwards, the team determines the severity of each of these failures by using a 10-point scale. 1 represents the least severe outcome, while 10 represents the most severe outcome. Once more, on a 10-point scale, the project team measures the probability of a failure occurring. 1 is the least probability of a failure occurring while 10 is the highest probability of a failure occurring. Finally, on a scale of 1 to 10, the team measures the likelihood of detecting an error before the customer does. If the probability of discovering an error is easy, it is rated 1. However, if it is impossible to detect, it is rated 10.

FMEA in six sigma helps eliminate and reduce errors that would, otherwise, have occurred in an organization’s process. By performing FMEA, project teams are able to identify and evaluate the effects of likely failures in an organization’s processes before they occur. Thus, FMEA improves audit processes, resulting in reliable and sturdy processes.

RPN in Six Sigma

RPN stands for Risk Priority Number. RPN in six sigma is applied when performing FMEA. It is a measure for ranking the risk of failure from the highest to the lowest. RPN is obtained by multiplying the three potential causes of failure; severity, occurrence and detection. Hence, RPN = Severity × Occurrence × Detection.

Severity is a rating for how the customer will detect a failure. Occurrence is a rating of the probability that a failure will occur in the process. On the other hand, detection is a rating for the effectiveness of the measures used to prevent easy detection of failure before the customer.

Besides, when FMEA is performed, the project team obtains the figures for potential causes of failure. These are scores they assign to each of them, using the 10-point scale. Thus, each potential cause of failure will rank from 0 to 1000.

As a result, the component with the highest RPN should be targeted for improvement. This is because it is an indicator of the weakest link in the process. Therefore, bringing down the number of errors helps to decrease the RPN. It also proffers a long-term solution to fixing the failure. However, the most cost-effective of the three components is occurrence.

Despite the fact that a higher RPN value indicates a higher chance of failure, this might not always be the case. As a general rule, any failure mode that has a high severity rate (9 or 10) should be considered first, irrespective of the overall RPN values. This is because severity carries the most weight in risk-assessment. The next point of consideration should be the highest combination of severity and occurrence.

FMEA Examples

FMEA examples exist to buttress its importance in six sigma. However, for the purpose of this article, we will be looking at two examples. These illustrate the role of FMEA in six sigma very well.

Gamma Knife radiosurgery example

In the first FMEA example, a healthcare organization set up a team of medical physicists, schedulers, neurosurgeons, operating room technologists, radiation oncologists, nurses and radiation safety officers. They were required to conduct FMEA for Gamma Knife radiosurgery. An expert on Gamma Knife was also included in the team.

They assessed the risk of failure based on the probability of occurrence, severity and the probability of detection of a failure. Next, the team rated the components on a scale of 1 to 10. Then, calculated the RPN value and coefficient of variation each component. Furthermore, the project team ordered their FMEA according to RPN value and severity scores.

By so doing, the team identified 86 failure modes in the process. Out of the 86, 40 were caused by the inappropriate use of radiosurgery headframe, skull definition tools, imaging fiducial boxes, Gamma Knife helmet and plugs, along with other features of the Gamma Plan treatment.

Based on the FMEA performed, the other 46 failure modes related to registration, contouring process, image transfer, imaging, which are common errors that occur in external beam radiation techniques. The FMEA with higher scores related to overlooked target areas, unsecured plugs, undetected machine failure, imperfect frame adaptor attachment and bad fiducial box assembly.

Nevertheless, the project team was able to gain a thorough understanding of the overall process of Gamma Knife radiosurgery from FMEA. In addition, FMEA helped the project team to identify likely steps that would result in the failure of the process. This makes it one of the good FMEA examples out there.

FMEA in a healthcare organization

Similarly, another healthcare organization set up a multidisciplinary team to administer FMEA on surface image-guided, Linac-based radiosurgery process. As a result, the project team drafted a process map to understand the steps involved in the radiosurgery. They went further to identify the failure modes for each step involved in the process. In addition, the project team calculated the RPN. With the RPN value, the team was able to determine the highest potential cause of failure.

The project team identified 167 failure modes. 25 of them produced an RPN value greater than 100. Thus, the team employed strategies to bring down the RPN from 288 to 72.

However, the FMEA implemented revealed that the use of surface image-guided, Linac-based radiosurgery does not increase the failure of Linac-based stereotactic radiosurgery process. Rather, it helps to reduce it.

Six Sigma Tools

Six Sigma is a management tool used for performing quality improvement in organizations. It helps to reduce and/ or eliminate errors and defects that have a negative impact on the customer’s experience. A variety of six sigma tools are useful in accomplishing this.

1.      FMEA

Depending on the process, there is a number of six sigma tools that can be used to implement quality improvement. FMEA is one of them. FMEA in six sigma is performed to detect the chances of errors in products, processes and services. In addition, FMEA helps to fix likely errors that have been identified, before they occur.

2.      Kaizen

This is another six sigma tool. Kaizen means continuous improvement. this six sigma tool is used to observe, determine and perform incremental improvements in processes. It is based in the philosophy that anything, no matter how small, can be improved upon.

Furthermore, kaizen is the responsibility of everyone. It encourages teamwork and employee involvement in implementing improvements.

3.      Poka-yoke

On the other hand, poka-yoke is a six sigma tool that enables employees to collaborate in order to determine the causes of human errors in the process. After the cause has been identified, they eliminate the problem by fixing it. Poka-yoke is a Japanese word that translates to “mistake proofing”.

4.      Pareto chart

Pareto chart is a graphic six sigma tool. It shows the disparities that exist in a set of data. The project team can use this chat to easily identify the highest cause of failure. It reveals 20% of the sources of 80% of the defects that exist in processes.

Pareto chart is analysed along two axes; the y-axis and the x-axis. The y-axis represents a total percentage and an error frequency, while the x-axis represents the categories of response variables. The x-axis is usually presented in a bar form.

5.      Regression analysis

Likewise, regression analysis is a statistical six sigma tool used to analyse and estimate the mathematical relationship between two variables. Also, it can be used to determine the relationship that exists between a set of inputs and output variable. For example, if y is an output variable, x1, x2, x3 etc will be a set of input variables.

6.      Value stream mapping

Another six sigma tool is value stream mapping. This tool is employed during the Analyse stage of DMAIC. Value stream mapping is used to show how information and resources flow within the process. Also, it enables organizations to make the most effective use of their resources. This tool helps to narrow organizational processes in a way that it becomes swift and concise.

Value stream mapping removes wait times between successive steps in a process. As the name implies, this six sigma tool helps organizations to identify value-adding and value-enabling activities in order to enhance them. On the other hand, it also identifies non-value adding activities in order to eliminate them.

7.      5S and 5-why

Furthermore, 5S and 5-why are other tools used in implementing six sigma. 5S is a method that focuses on eliminating errors by organizing the workspace. The 5S represents sorting, setting in order, shining, standardizing and sustaining. In the same vein, 5Why helps to investigate the root cause of errors by asking “why” questions.

Conclusion

Failure Mode Effect Analysis (FMEA) is a six sigma tool that evaluates a product, process or service in order to determine the probability of a failure occurring. By performing FMEA, organizations can identify failures that may occur in their processes before the customer detects them. A number of FMEA examples exist to buttress this fact.

Basically, there are two types of FMEA. They are Process FMEA (PFMEA) and Design FMEA (DFMEA).

To effectively perform FMEA, a project team needs to be set up. This team takes a series of steps. Firstly, they compile a list of possible failures, then, measure the effects of these failures. Next, the team scores severity, probability of a failure occurring and the likelihood of detecting an error before the customer, on a scale of 1 to 10.

Furthermore, the project team calculates the RPN value by multiplying severity, occurrence and detection. RPN is ranked from 0 to 1000. Consequently, a high RPN value indicates a high probability of failure and vice versa. Although, this may not always be the case.

FMEA is one of the many six sigma tools used for quality improvement. Other six sigma tools include 5S, 5-why, value stream mapping, regression analysis, Pareto chart, poka-yoke and kaizen.

In conclusion, FMEA in six sigma helps to identify and evaluate errors before they occur. It allows comprehension, comparison and further analysis.

For more about quality improvement methods, feel free to explore the following articles:

Six Sigma in Healthcare: Concept, Benefits and Examples

Lean in Healthcare – History, Tools & Examples

Total Quality Management Principles, Concept and Importance

Quality Improvement in Healthcare – Framework & Methodology