Understanding FMEA evaluation criteria and risk assessment

FMEA evaluation criteria are the specific measurements and scales used to judge how serious a potential failure could be (severity), how likely it is to happen (occurrence), and how easily it can be detected (detection). These criteria help you consistently assess the impact of a failure, its probability, and how well current checks can find it.

Risk assessment in FMEA involves using these criteria to determine the overall risk associated with each identified failure mode. This typically culminates in a Risk Priority Number (RPN) or an Action Priority (AP) rating, which helps you prioritize corrective actions. A higher RPN or AP indicates a greater need for immediate attention and risk reduction efforts.

These evaluation and risk assessment criteria are applied to your FMEA data and displayed in FMEA formsheets. You can view failure effects, failure causes, and related actions in the formsheet. The About changing the default style and structure of the formsheet are determined by the FMEA guidelines you specify when creating FMEA objects.

FMEA guidelines are predefined rules and standards that provide a structured framework for evaluating and managing FMEAs. They ensure consistency in creating, managing, and using FMEA data.

Consider you are conducting an FMEA analysis for a car's braking system. The FMEA you create includes failure modes (for example, brake failure), effects (for example, reduced braking efficiency), causes (for example, worn brake pads), and actions (for example, replace brake pads). The guidelines associated with these FMEA objects provide standard definitions, rating scales, and procedures for documenting and managing the analysis.

Teamcenter provides several FMEA guidelines based on the following industry standards for design and process FMEA:

• AIAG & VDA

• IATF 16949

• AS13004

• AS13100

These standards provide detailed guidelines on various aspects of FMEA, including the appearance of formsheets, the use of risk priority numbers (RPN) or action priority ratings, and the structure of risk metrics.

If the out-of-the-box guidelines do not fully meet your business requirements, you can modify the action priority and risk priority of these guidelines accordingly. However, if your business requirements are significantly different than what is provided in the out-of-the-box guidelines, you create a new FMEA guideline.

Example:

The AIAG & VDA standard recommends that for a design FMEA, if the severity is 9-10, occurrence is 2-3, and detection is 5-6, the action priority is medium. This is because,according to this standard, if the RPN is less than or equal to 200, the action priority is medium.

Consider a car manufacturer producing a safety-critical component for the car. Even though the occurrence is low (2-3), safety cannot be compromised. In this case, the manufacturer can choose to modify the out-of-the-box guideline by increasing the severity range to 11-15 (instead of 9-10), the occurrence range to 4-5 (instead of 2-3), and retaining the original detection range of 5-6. With these modified values, the minimum value of the RPN is 220 and would be classified as a high priority, indicating immediate action is required. This is because per the AIAG & VDA standard, if the RPN is more than 200, the action priority is high.

Now, consider a scenario where the manufacturer is producing a highly specialized component for a defense aircraft. The aerospace industry has its own unique safety needs, which will not be addressed by a standard widely used in the automotive industry. In this case, the manufacturer would likely create a new FMEA guideline that meets their business requirements.