Types of FMEAs
All FMEAs focus on design and assess the impact of failure on system performance and safety. However, FMEAs are generally categorised based on whether they analyse product design or the processes involved in manufacturing and assembling the product.
• Product FMEAs–Examine the ways that products (typically hardware or software) can fail and affect product operation. Product FMEAs indicate what can be done to prevent potential design failures. As a result, product FMEAS are also called design FMEAs.
• Process FMEAs–Examine the ways that failures in manufacturing and assembly processes can affect the operation and quality of a product or service. Process FMEAs indicate what can be done to prevent potential process failures prior to the first production run.
Although FMEAs can be initiated at any system level and use either a top-down or bottom-up approach, today’s products and processes tend to be complex. As a result, most FMEAs use an inductive, bottom-up approach, starting the analysis with the failure modes of the lowest level items of the system and then successively iterating through the next higher levels, ending at the system level. Regardless of the direction in which the system is analysed, all potential failure modes are to be identified and documented on FMEA worksheets (hard copy or electronic), where they are then classified in relation to the severity of their effects.
In a very simple product FMEA, for example, a computer monitor may have a capacitor as one of its components. By looking at the design specifications, it can be determined that if the capacitor is open (failure mode), the display appears with wavy lines (failure effect). And, if the capacitor is shorted (failure mode), the monitor goes blank (failure effect). When assessing these two failure modes, the shorted capacitor would be ranked as more critical because the monitor becomes completely unusable. On the FMEA worksheet, ways in which this failure mode can either be prevented or its severity lessened would be indicated.