DFMEA


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DFMEA - short version

Design Failure Mode & Effects Analysis.



DFMEA - long version

Design Failure Mode Effects Analysis (DFMEA) is the application of the Failure Mode and Effects Analysis method specifically to product design. It is a paper-and-pencil analysis method used in engineering to document and explore ways that a product design might fail in real-world use. A DFMEA documents the key functions of a design, the primary potential failure modes relative to each function and the potential causes of each failure mode. The DFMEA method allows the design team to document what they know and suspect about a product's failure modes prior to completing the design, and then use this information to design out or mitigate the causes of failure.

Ideally, the DFMEA is begun at the earliest stages of concept development, and can then be used to help winnow down competing designs and to help generate new, more robust concepts. DFMEA attempts to quantify the likely severity and frequency of occurrence of each failure mode, as well as the ability of the design to detect each failure cause by using an ordinal scale (typically 1 - 10, where one is "best" and ten is "worst"). Those failure modes and causes with the highest scores should then be addressed through product redesign. DFMEA is fundamentally a team effort, and therefore should only be performed with the design team as a whole.

The method of the DFMEA process is usually as follows. First, the known functions of a system or component are written down. These are usually drawn from the product requirements, bill of materials (BOM) and prior experience of the engineering team. Next, for each function, a list is made of ways in which the product might fail to meet the functional requirement; these are known as the failure modes. For instance, the main functions of a pencil sharpener are to sharpen pencils to a fine point and to catch the tailings from sharpening. The failure modes may include not sharpening at all, frequently breaking the graphite and not catching the tailings.

Once failure modes are identified, the product design is reviewed and potential causes of the failure modes are identified. The team then ranks the severity of the failure mode, using a 1 to 10 scale, where a "1" indicates that there is no discernible effect and a "10" indicates that the failure mode may impact safe operation and/or violate government regulations. Next, the frequency of occurrence of the failure mode is ranked using a scale from "1," remote likelihood of failure, to "10," persistent failures. Each cause of failure is then evaluated for the ability of the design controls to detect and prevent the failure mode.

Finally, a Risk Priority Number (RPN) is calculated by multiplying the severity, occurrence and detection rankings together. With RPNs calculated, the next action by the design team depends on the stage of development. In the concept development stage, the RPNs may be used to compare various designs and select the best among them, or as an input to sensitivity analysis when combining features of the best concepts. Later in the development process, the RPNs should be used by the developers as a guide to focus development effort in order to make the product safer and more robust. After production launch, the RPNs should be used to select design features for continuous improvement activities.



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