Step 4 of the standardized FMEA method description:
Summary: Failure analysis
The essential input variables for the failure analysis, which is the 4th step of the FMEA according to the standardized FMEA method description, are the results of the functional analysis. The failure analysis involves correctly negating functions in terms of language and content. Clarity of expression is important in this context. Leaks and associated unfulfilled requirements must be clearly identified. These requirements specify the functions and if they are also negated, it is possible to describe potential consequences of failure realistically, primarily at the highest level.
At the next level, the design of the product features from the functional analysis are negated in the failure analysis. If the resulting insights in the failure analysis of the FMEA are then linked in terms of malfunctions, at the lowest level the incorrect design automatically becomes the cause, while the leak at the next highest level is the failure. Negation at the highest level is the consequence.
- The malfunctions at the various levels of the structure created define causes, failures and effects.
- The cause emerges at the level of the part design.
- The leak at the system level is the failure.
- At the overall system level, the effect is that the function does not fulfil the requirements of the system.
Detailed knowledge: Failure analysis in the FMEA method description
The main objectives of the failure analysis in the FMEA are:
- Establishing chains of failure effects.
- Defining failure modes, failure effects and failure causes.
- Identifying failure causes with the aid of P-diagrams and failure networks (D-FMEA) or Ishikawa and fishbone diagrams (P-FMEA).
- Coordinating the cooperation between supplier and customer (failure effects).
- Establishing the basis for the documentation on the FMEA form and in the risk documentation.
In the failure analysis of the FMEA, failures, failure effects, failure modes and failure causes are examined. Failures can manifest themselves in different ways – from loss of function and unintended function (D-FMEA) to non-conformity and unnecessary activity (P-FMEA). The description in the failure analysis is in the context of the loss or limitation of the function, to which several failures may be linked. They must all be described clearly and comprehensibly.
The failure analysis of the FMEA covers the three aspects of failure effect, failure mode and failure cause. Failure effects here are the consequences of a failure mode. In the D-FMEA, they are described for the next level of product integration (internal) or the end user (external). In the P-FMEA, they relate to the function of the process element.
Failure modes are defined in the FMEA handbook (AIAG & VDA) as the way in which a component does not complete or is unable to deliver the intended function. They are derived from the functions and must be described with the technically correct terms in the failure analysis of the FMEA. Examples of failure modes are interrupted signals, inadequate fixings or pressure loss (D-FMEA) and unstable operation or incorrectly assembled parts (P-FMEA).
Each cause of a failure is a clear indication of why the failure can occur. The effect is the failure mode. Failure causes can be derived from the failure modes of the function, requirements of the next lowest element and potential disruptive factors. The typical failure causes in the P-FMEA include Ishikawa’s 4M categories: man, machine, material, measurement.
Functional analysis in the FMEA method description: Failure analysis
Consideration of a failure as a failure effect, failure mode or failure cause depends on whether the system level, subsystem level or component level is being examined. For the links, the focus is on the questions “why does the failure occur?” (failure cause and failure mode) and “what happens when the failure occurs?” (failure effect and failure mode).
The complete failure analysis of the FMEA with the precise description of all potential failures, their interdependencies and causes is the basis for the risk analysis as the 5th step in the standardized method description in the AIAG & VDA handbook.