Step 5 of the standardized FMEA method description:
Summary: Risk analysis
The input variable for the risk analysis of the FMEA is consequently the result of the previous step, the failure analysis. The risk analysis, which is the 5th step of the FMEA according to the standardized FMEA method description, involves assessing the quality of the existing or planned action. A distinction is essentially made between two large categories of actions here:
- Through preventive actions, the likelihood of occurrence of the cause-failure relationships is minimized.
- In addition, detection actions must be defined.
For each of the two categories of actions in the risk analysis of the FMEA, there is now a separate assessment scheme in the handbook (AIAG & VDA). With the 7 steps of the standardized FMEA method description, tables and catalogs have been created to assess the likelihood of occurrence and likelihood of detection in the risk analysis of the FMEA.
There are two crucial points in the risk analysis of the FMEA for carrying out this step, defining the corresponding actions and assessing their effectiveness:
- The likelihood of occurrence, the so-called O value, is a quality assessment of the preventive actions discussed.
- On the other hand, the likelihood of detection, the so-called D value, is a quality assessment of the detection actions under consideration.
In addition to the likelihood of occurrence and likelihood of detection, the risk analysis in the standardized FMEA method description incudes a third crucial factor: the severity of the effects. It is important in this context to draw up clear customer categories:
- The first customer perspective is the customer’s own company, with consideration of the damage caused to that company. Examples include rejects, rework and extra work on the project.
- The second customer perspective is the system integrator, the assembly plant to which we deliver our results. This involves defining potential effects, such as additional work in assembly or rejection in incoming goods inspection.
- The third customer perspective is the user of the entire system, such as the automobile driver, for whom entirely different assessments must be formulated: system failure, for example, which means that the automobile cannot be driven. Or the failure of subsystems which mean that the car can still be used, but not to its full extent.
- The fourth customer perspective, which should not be underestimated either, is society, expressed through technical standards, official and statutory requirements.
The combination of the likelihood of occurrence with the effect or the likelihood of detection with the effect then result in the two-dimensional matrices of the risk analysis in the FMEA, in which the risks are displayed. According to the FMEA handbook (AIAG & VDA), these are classified into high, moderate and low in the standardized FMEA method description.
Detailed knowledge: Risk analysis in the FMEA method description
In the risk analysis of the FMEA, risks are assessed by analyzing their severity, occurrence and detection and identifying any necessary action.
The objectives of the risk analysis in the standardized FMEA method description are:
- Definition and assessment of existing and planned actions.
- Presentation of interdependencies between preventive actions and causes of failure or detection actions and causes of failure.
- Assessment of severity, occurrence and detection for the respective chains of failure effects.
- Establishment of the priorities for the necessary tasks.
- Cooperation between supplier and customer, creation of a shared understanding of the technical risks.
- Creation of the starting point for optimization, e.g. by defining additional design or testing actions.
Design actions in the risk analysis of the FMEA is the term used for experiences from comparable existing designs. The preventive actions and detection actions are the key parts of the documentation. Preventive actions provide rules and information as input for the design. Detection actions provide established verification and validation procedures by means of which it has been shown that failures have been detected in the past. Important: The effectiveness of the preventive and detection actions applied in the risk analysis of the FMEA should be confirmed by reviews or project documents.
Risk analysis in the FMEA method description: Assessment and task priorities
In the risk analysis, the interplay between failure effect, failure mode and failure cause is examined in terms of its risks. Severity (S) stands for the severity of the failure effect. Occurrence (O) stands for the occurrence of the failure cause and detection (D) for detection of the failure cause/mode that has occurred. Assessment values between 1 and 10 are assigned to each of these risk assessment criteria in the risk analysis according to the FMEA handbook (AIAG & VDA).
If failure modes, failure effects and failure causes are defined in the detailed risk analysis along with severity assessments, occurrence assessments and detection assessments, actions to reduce risk can then be established. At this point in the risk analysis of the FMEA, the FMEA team has to define these in a reasonable way and in accordance with resources, technology and individual factors.