Related Topics:

Background: FMEA and Related Analyses

Basic Analysis Procedure for FMEA

The following list describes the basic analysis procedure for FMEAs and these steps are described in more detail in the sections that follow.

Determining the Scope

Before you can begin the FMEA, you must decide what you are going to analyze. Determining the scope of the analysis is an extremely important step because it helps to identify which FMEA(s) will be performed and then, for each particular FMEA, the boundaries for what issues will be considered and the approach that the analysts will take during the analysis. The determination of the scope may be based on a variety of factors, including (but probably not limited to) timing, complexity and characteristics of the design, risk/importance, available budget, customer requirements, etc. The tools available for determining the scope will vary depending on whether you are performing a design FMEA or a process FMEA.

For Design FMEAs

If you are performing a design FMEA, you may wish to start by defining the system configuration. For example:

Early in the design process, you may wish to perform a high-level FMEA on the entire system. As the design matures, it will be possible to perform more detailed FMEAs on individual assemblies or components. A change point analysis or preliminary risk assessment may help to focus the analysis effort on the aspects of the design that have the greatest risk and/or have the greatest potential benefit from design improvements. Factors may include:

Tip: There are many different ways that the preliminary risk assessment can be performed. The Risk Discovery Analysis in Xfmea supports two possible methods: one based on a series of yes/no questions and another based on rating scales.

For each individual FMEA that you will perform, it is useful to define what components and interactions will be included in the analysis. A boundary diagram (or block diagram) shows the physical and logical relationships between the components in the system or assembly. It can identify relationships and dependencies between components as well as critical inputs and outputs.

Tip: In Xfmea, you can use the Attachments feature to provide easy access to boundary/block diagrams that have been created with other software tools (such as Visio or PowerPoint).

Alternatively, you can use the FMEA Block diagram feature to create the diagram and link it to the rest of the analysis

For Process FMEAs

If you are performing a process FMEA, you may start by identifying the steps in the process and the operations that must be performed at each step. For example:

In most cases, the scope of the PFMEA will be the entire process. However, in some situations, the organization may choose to exclude low-risk portions of the process.

The process flow diagram (PFD) provides a logical, visual depiction of the process that is being analyzed. The diagram typically uses specific symbols to describe different types of activities (e.g., operation, decision, inspection, storage, etc.). It also may include an identification of the product or process characteristics that need to be monitored at each step (e.g., temperature of the oven, thickness of the wax, diameter of the hole, etc.) and the possible sources of variation (e.g., incorrect setup, contamination, machine maintenance, etc.). Such diagrams can be useful to determine the steps in the process that will be analyzed in the PFMEA and to determine the functions and critical characteristics that will be considered in the analysis.

Tip: In Xfmea, you can use the Attachments feature to provide easy access to process flow diagrams that have been created with other software tools (such as Excel, Visio or PowerPoint).

Alternatively, you can use the process flow diagram feature to create the diagram and link it to the rest of the analysis.

Assemble the Team

One of the first steps in performing an FMEA is to assemble a cross-functional team of knowledgeable individuals to perform the analysis. The team should be large enough to make sure that relevant viewpoints and knowledge are represented but not too large. If the team is too large, it will be difficult to have productive discussions during meetings and it will be a waste of an extremely valuable resource – the time and patience of your organization’s subject matter experts. Team members should be familiar with the FMEA analysis process, as it is practiced by the organization. In addition, a skilled facilitator can help to make sure that team meeting time is used effectively and the analysis is performed correctly.

The composition of the team at any particular meeting may vary depending on the focus of the discussion. This may include representatives from:

  • Design

  • Quality/Reliability

  • Analysis/Testing

  • System Integration

  • Materials

  • Field Service

  • Suppliers/OEM

  • Maintenance

  • Manufacturing/Assembly

  • Etc.

 

Tip: In Xfmea, you can use the analysis plan feature to document the members of the analysis team for each FMEA.

Establish the Ground Rules and Assumptions

Before beginning the analysis, the team should discuss (and probably document) the underlying assumptions of the analysis and specific ground rules for how the analysis will be performed. Some of these guidelines may be determined already by the organization’s standard practices for FMEA and some may be specific to the particular analysis project. Some of the questions that might be considered include (but are not limited to) the following:

This list is provided as an example. Other issues may be applicable for your particular situation.

Tip: In Xfmea, you can use the analysis plan feature to document the ground rules and assumptions for each FMEA.

Gather and Review Information (Pre-Work)

Taking the time to gather and review available information before the analysis meetings begin can help to make the most efficient use of team meeting time and achieve an analysis that is thorough and accurate. The appropriate resources will vary depending on the type of FMEA that you are performing and the specific product or process that you are analyzing. If you are performing a design FMEA, some of the resources that you may wish to consult include (but are not limited to) the following:

If you are performing a process FMEA, some of the resources that you may wish to consult include (but are not limited to) the following:

These lists are provided as examples. Other resources may be applicable for your particular situation.

Tip: In Xfmea, you can use the Attachments feature to provide easy access to supporting documentation that may be relevant to a particular analysis.

Identify the Functions, Failure Modes, Effects, Causes and Controls

For each item or step that will be analyzed, the analysis team will use engineering and business judgment to identify the functions, failure modes, effects, causes and controls that will be considered in the analysis.

In the case of process FMEAs, some practitioners have chosen to identify the effects on the assembly plant, the assembly/system and the end user.

Tip: In many situations, an existing document may contain information that would be useful to import directly into your FMEA analysis (such as a requirements document, a process flow diagram worksheet, an FMEA from a similar product/process or a predefined "phrase set"). Xfmea provides numerous features to help you find and import this information. These features are described in Importing and Exporting.

Evaluate Risk for Potential Failures

A typical FMEA incorporates some method to identify and evaluate the risk associated with the potential problems identified through the analysis. Risk Priority Numbers (RPNs) and criticality analysis are the most commonly used methods for this.

Risk Priority Numbers

To use the Risk Priority Number (RPN) method to assess risk, the analysis team must:

RPN = Severity x Occurrence x Detection

RPN rating scales usually range from 1 to 10 (or 1 to 5), with the higher number representing the higher seriousness or risk. Sample rating scales are provided in the major industry standards and various textbooks and manuals that address FMEA analysis. In addition, the scales may be created/modified by the analysis team to fit the organization’s requirement or the characteristics of a particular analysis.

In some cases, the RPN may be used as a "threshold" to trigger corrective action. For example: "If the RPN is greater than <?>, corrective action is required." Another approach is to start from the issue with the highest RPN and work down the list. Other organizations might establish policies that require corrective actions to be evaluated for the top 20% of issues. And so on....

However, it is important to remember that the RPN is the product of three subjective ratings and different circumstances may produce similar or identical RPNs. For example, an RPN of 100 could mean:

When you consider the different situation posed by each of these scenarios, it is easy to see that basing decisions solely on the RPN may not be appropriate. Therefore, many FMEA practitioners have chosen to look at the ratings and RPNs in other ways. Some of these alternative approaches are described next.

With whatever approach is selected, it is important to remember that RPN ratings are relative to a particular analysis. An RPN in one analysis is comparable to other RPNs in the same analysis but an RPN may NOT be comparable to RPNs in another analysis. RPNs are a tool to evaluate risk and prioritize corrective action. The goal of the FMEA is to reduce risk, not just RPN.

Tip: Xfmea provides an extensive array of features to support risk assessment based on RPN and related metrics. These are described in detail in Risk Priority Numbers (RPNs).

Criticality Analysis

The MIL-STD-1629A document describes two types of criticality analysis: qualitative and quantitative. Both types of criticality analysis consider the probability that the failure will occur and the severity of the potential failure. However, the "quantitative" method incorporates the item’s unreliability, which can be determined quantitatively.

To use qualitative criticality analysis to evaluate risk and prioritize corrective actions, the analysis team must a) rate the severity of the potential effects of failure and b) rate the likelihood of occurrence for each potential failure mode. It is then possible to compare failure modes via a Criticality Matrix, which identifies severity on the horizontal axis and occurrence on the vertical axis.

To use quantitative criticality analysis, the analysis team considers the reliability/unreliability for each item at a given operating time and identifies the portion of the item's unreliability that can be attributed to each potential failure mode. For each failure mode, they also rate the probability that it will result in system failure. The team uses these factors to calculate the criticality for each potential failure and for each item.

Tip: Xfmea supports quantitative and qualitative criticality analysis patterned after the concepts in MIL-STD-1629A. This functionality is described in detail in the Criticality Analysis topic.

Identify and Assign Corrective Action(s)

The next step is to identify, assign and track the completion of recommended actions that will help to reduce the risk associated with potential failures. In some situations, it may be possible to take an action that will reduce the severity of the effect when the failure occurs but in most cases, the recommended actions will be designed to either reduce the likelihood that the failure will occur or to increase the likelihood that it will be detected and controlled before the problem reaches the end user. When selecting the actions to recommend, the team may consider:

Tip: One of the most costly mistakes among FMEA practitioners is the failure to follow up and track the completion of recommended actions. Xfmea provides multiple features that will help to ensure that your organization implements the actions suggested by the analysis in order to achieve the benefits that come from improving the design and reducing the risk. These are described in Actions.

Perform Corrective Actions and Re-evaluate Risk

In many cases, it may be appropriate to revise the risk assessment after the recommended actions have been completed (or based on the results that the analysis team expects to achieve when they are completed). This will provide an indication of the effectiveness of corrective actions and the benefits achieved by performing the FMEA. To use revised RPNs for this purpose, the analysis team will:

The % reduction in RPN can be calculated with the following equation:

Distribute, Review and Update Analysis Results

FMEAs are typically reported in a tabular (worksheet) format. The style varies depending on the standard/guidelines and the terminology used during the analysis. In addition to the worksheet, other tabular reports can be useful to support decision-making and communicate the results of the analysis, such as Assigned Actions, Causes Ranked By RPN, etc. Pareto (bar), pie and matrix charts also can help to visualize analysis results.

An FMEA is most effective when it is a "living" document. When completed, the analysis should be distributed as appropriate throughout the organization so that it can be used as a resource for other activities. Your organization invested too much effort and knowledge to bury the document in the file cabinet!

Tip: In Xfmea, you can use the Reports window and the Query Utility to create the reports that you will use to distribute the results of your FMEAs.

In addition, the Plot Viewer provides a variety of charts to present the information graphically.

In general, the FMEA should be reviewed and updated:

Tip: In Xfmea, there are several ways to manage revisions to an existing analysis, including a formal change log that can automatically record all revisions to an existing analysis and facilitate a process for electronic approval tracking. These features are described in Change Logs.

After the completion of an FMEA project, it can be a good idea to have an expert in the FMEA methodology evaluate (audit) the FMEA. In addition, you may wish to solicit feedback from the team members who participated in the analysis in order to identify issues that should be addressed in future analysis projects. A suitable checklist could be obtained from the FMEA literature or your organization may choose to develop its own audit requirements.

Tip: In Xfmea, you can use the analysis plan feature to document the results of the quality survey for each FMEA.

 

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