The 7 steps of FMEA according to the VDA/AIAG harmonization
Step 3 of the standardized FMEA method description:
Summary: Functional analysis
In the functional analysis, which is the 3rd step of the FMEA according to the standardized FMEA method description, the focus is on the question: what does the thing that we want to analyze do? On this basis, the object of analysis and the subsystems are examined in the functional analysis, as presented in the structural analysis. The results of the structural analysis are thus a crucial input for the functional analysis, in which it is a matter of drawing up rules as to how functions are correctly described from a technical point of view. The functional analysis is at the heart of any successful FMEA. Parameter diagrams (P-diagrams) are frequently used to describe the functions precisely.
The main recommendations for precise description in the functional analysis are:
- Please do not use any colloquialisms: we need as clear an understanding as possible of the function of all elements of the object of analysis.
- Each function consists of a noun with a dynamic verb that describes the physical effect. Examples include injecting diesel, applying torque, transferring heat. Functions and requirements should also be clearly distinguished from one another in the functional analysis.
- Individual components do not necessarily have functions, they are the providers of the product features that can be properly linked in terms of function. The function belongs to the assembly.
- The functions of all the levels and system elements are linked to form functional networks. The key questions are why? and how?
Detailed knowledge: Functional analysis in the D-FMEA method description
Purpose and objectives
In the functional analysis, the functions specified in the requirements are assigned precisely to the corresponding system elements (D-FMEA) or the process/product (P-FMEA).
The objectives of the functional analysis are:
- Detailed graphical representation of the function (visualization)
- Creation of a functional tree/network and a functional analysis form and P-diagram (D-FMEA) or process flow chart (P-FMEA)
- Detailed gradation of the external and internal customer functions and their requirements in the analysis
- Linking of the defined requirements and characteristics
- Specification of the practical cooperation of the development team
- Precise definition as the basis for the 4th step in the standardized method description, the failure analysis.
Functional analysis in the FMEA method description: Function
The function in the functional analysis describes the purpose of the system[/tooltip]element under consideration (D-FMEA). Important: the functional description should be clear. Moreover, the functional analysis describes the relationship between input and result with the aim of carrying out the task at hand. In addition to the main functions, any auxiliary functions that occur are analyzed and included.
In the P-FMEA, the function describes the intended purpose of the respective process step, causal element and process element. The description of the function should be absolutely comprehensible at the end of the functional analysis.
Functional analysis in the FMEA method description: Requirements/characteristics
In the D-FMEA, a distinction is made in the functional analysis between two groups of requirements: the functional requirements and the non-functional requirements. A functional requirement is a criterion for the measurability of the performance of the function. It may be derived from external or internal sources, e.g. statutory or official specifications such as ISO 9001 and ISO 26262 (Functional safety). In addition, there are various internal requirements – from the requirement specification, through compatibility and testability, to reusability and cleanliness.
In the functional analysis of the P-FMEA, a characteristic is a typical feature of a product. It describes e.g. the diameter or the surface structure. Requirements are described here as product characteristics or process characteristics, which relate specifically to the performance of the process function. The mode and cause of failure can be derived from this.
Functional analysis in the FMEA method description: Visualization and P-diagramA parameter diagram shows the environment in which the object exists. It consists of dynamic inputs and factors that affect the system. The individual factors of the P-diagram influence the input and result. With the aid of this graphical representation, the behavior of a system or an individual component is visualized in the functional analysis.
In the P-FMEA, the links and interactions between functions, process elements, causes and process steps are illustrated in functional networks, functional trees or a functional matrix. This frequently also depends on the FMEA software used.
The result of the functional analysis is the basis for the failure analysis as the 4th step in the standardized method description in the AIAG & VDA handbook.