Performing Failure Mode and Effect Analysis

DFMEAs are initiated during the conceptual phase of new product development. A DFMEA provides an analytical analysis of the potential failure modes and associated causes. By considering the failures associated with a design — including safety, quality, cost, performance and reliability — the processes associated with development or manufacture will be significantly reduced. Additionally, the development of specifications associated with the offering will ensure a product capable of meeting defined requirements.

The example below shows the use of DFMEA during the development of a new sensor. Note the use of critical characteristics under the “Class” column. Critical characteristics are identified during the design of a product to call out aspects that must be given special attention. Critical characteristics are often defined as a product requirement (i.e. dimension, feature, performance aspect) of such significance that if defective or inadequately produced, it would cause personnel injury, loss of station or loss of mission (such as critical bolt torquing specified by drawings and/or procedures). Critical characteristics are identified on applicable drawings/specifications for the hardware/software under surveillance. Companies use various symbols for identifying critical characteristics. At Watlow, for example, a black diamond ( ) is used in the DFMEA to call out a requirement needing special attention.

Once the DFMEA is completed, the PFMEA can be developed to control the production process. At Watlow, PFMEA documents are developed based on part numbers. This means the PFMEA lists the steps for the build of a part from receipt of materials through to shipping. The disadvantage of this approach is that when a change is made to a process common to more than one part number, all PFMEA documents containing references to that process must be changed. Using a process structure — versus the part number structure — it becomes clear as to the benefits gained by focusing on the process. Take Watlow’s induction braze process as an example. If a PFMEA is developed for induction brazing, it can be applied to all part numbers that utilize the induction braze process. When improvements are made to the induction braze process, updates are made to the PFMEA specific to this process. The benefit is that only one change must be made on one document to cover all part numbers that use this process. Additionally, the PFMEA can be used to prioritize improvement using a RPN for a process that relates to many part numbers.