54 Chapter 5 Failure Modes Effects Analysis One of the tools that is used for both quality and reliability analysis is the FMEA. The FMEA is a tool that is designed to systematically evaluate potential ways in which a product or process could fail, to assess the risk of those failures occurring and finally to attempt to prioritize those areas where corrective actions are needed in order to mitigate those failure modes as well as to document the corrective actions that are implemented as a result of the FMEA and their results (American Society for Quality, 2014; Automotive Industry Action Group, 2014). The FMEA is generally broken into a couple of different areas:
concept FMEA (CFMEA), design FMEA (DFMEA), and process FMEA (PFMEA). The difference between them is only based on the area of focus and the timing during the development process. The CFMEA is focused on identifying the potential failure modes in the concept before the actual hardware is defined. More commonly done is a DFMEA which is focused on the product itself and identifying the potential areas where the product may fail.
For example, a DFMEA for a battery system could include an item such as “Potential for fasteners to loosen during vibration” which may cause a potential failure of, depending on the location of the fastener, a reduction in power, a potential to create an external short circuit, and an increase in heat generation and impedance due to the loose connection (these all assume that the fastener is used to connect a bus bar to a cell in this instance). The DFMEA then will evaluate the questions of how likely is this to occur, how often is this expected to occur, and what are the results of this failure.
It may then drive a discussion around the design which could result in the bus bars and cells being redesigned to use a welded terminal (thus eliminating the poten- tial for a fastener to loosen up). This is just a simplified example to help illustrate the DFEMA and how it works. On the contrary, the process and assembly FMEAs are totally focused on the process used to manufacture the product.
While this PFMEA could drive requests to the product team to make design changes, it is really focused on ensuring that the process is in place to ensure that the product, an energy storage system in our case, is assembled correctly and done in such a way as to minimize the potential for errors to occur during assembly. In this instance, the example may include a potential failure mode of a fastener not being fully driven or seated. The effect of this may be similar to the DFMEA example above; if it is for an electrical connection, a loose fastener may reduce contact between the bus bar and the cell terminal, causing a “bad connection” and a potential for a shortened life.
In this instance, the actions that are recom- mended are likely to be more process focused such as adding a torque detect feature during the installation to ensure that the fastener is fully seated. But it may also include the addition of features into the design that enable error proofing during the assembly process. Figure 2 shows the industry standard FMEA form. Organizations such as the Automotive Industry Action Group (AIAG) and the American Society for Quality (ASQ) offer standard FMEA tools and even offer training and certification on using the tool.