(AIAG: Southfield, MI) -- AIAG’s Potential Failure Mode and Effects Analysis (PFMEA), now in its fourth edition, has been the benchmark source for FMEA in the industry for many years. However, automakers and supplier leaders continue to point to concerns with the effectiveness of FMEA implementation in the supply chain. This may be due to a number of factors, including inadequate resources, or ineffective training of new quality practitioners.
To supplement the existing FMEA training, AIAG has developed a new workshop, “PFMEA in Context.” This class shows how FMEA and other advanced product quality planning (APQP) deliverables fit into the bigger system of product quality planning and realization (see AIAG’s Advanced Product Quality Planning with Control Plan reference manual). During this workshop, participants study the development and auditing of these documents, along with pitfalls to avoid and best practices documented by automakers, suppliers, and auditors.
“The class was excellent,” says Jared Peacock, a Toyota employee. “It really showed how the PFMEA and process flow, and control plan are connected and should be utilized to ensure quality throughout the process, and therefore ensure the part quality. The booklet we received as part of the training has been a great reference in my normal job activities.”
“As a supplier to automobile manufacturers, I found it very valuable to combine the content of the APQP and FMEA manuals into a single training course,” says Clark John of Timken. “The course highlighted the connectivity of the documents. The training triggered many ideas that I plan to incorporate into my company’s current practices to improve the effectiveness of our FMEAs.”
The AIAG FMEA manual defines FMEA as “an analytical methodology used to ensure that potential problems have been considered and addressed throughout the product and process development process. FMEAs are an effective tool to quantify risk so it can be analyzed, prioritized, mitigated, or eliminated.” FMEAs can be applied in all types of organizations, including manufacturing and service. FMEAs should be completed by a cross-functional team during product or process development as part of the APQP process.
Risk is generally quantified by using a risk priority number (RPN), which is calculated by multiplying ratings for severity (S) of problem by likelihood of occurrence (O) by likelihood of detection (D), or S × O × D = RPN. Use of arbitrary thresholds, for example, RPN > 40, is not recommended. Organizations should be working the highest priority risks regardless of the rating criteria or values. High severity ratings should always be addressed.
Appendix C in the FMEA manual offers alternative risk analysis criteria. One is called SOD or SD. It is a non-arithmetic combination of the ratings above. For example, for severity = 6, occurrence = 3, and detection = 7, the SOD rating would be 637. The SD calculation is the same, excluding the occurrence value. So the SD rating for the above example would be 67. The various SOD ratings would then be sorted in numerical descending order to get the highest severity scenarios at the top of the list.
Appendix D lists some alternative techniques to FMEA for analyzing risk. These include failure mode effects and criticality analysis (FMECA), design review based on failure modes (DRBFM), and fault tree analysis (FTA). Examples of some these are provided in the appendix.
The FMEA manual indicates that the FMEA scope “establishes the boundary of the FMEA analysis.” The scope can be system, subsystem, or component. A system consists of many subsystems, which consist of many components. The links and interactions among parts within the scope, as well as with other subsystems or systems, also must be addressed.
The FMEA manual lists a number of tools that can help define the appropriate scope, which should dictate the appropriate team membership. These include: block diagrams, process flow charts, schematics, and bills of material.
The FMEA manual also contains an index and list of helpful references. It adds numerous examples and diagrams to provide helpful guidance. There is a section on linking FMEA to other documents, including the block diagram and the design verification plan and report (DVP&R).
What constitutes an acceptable FMEA? A good FMEA should:
• Be completed across to the right side, which is the area for recomputing risk after initial efforts have been taken to reduce the initial high risk rating, e.g., RPN
• List multiple effects for each mode and multiple causes for each effect. Generally there is not a 1:1 relationship because any given failure mode could have many effects.
• List actions taken on high severity and high RPN, or other risk ratings, aimed at preventing the occurrence of a potential failure. Responsibility for the actions taken should be assigned and tracked to completion.
• Include efforts to error-proof the design or process; see AIAG’s Effective Error-Proofing (CQI-18).
• Ensure that measurement uncertainty is known and acceptable for applicable metrics.
• Identify characteristics that should be designated as “special” or critical on the control plan so actions can be planned and implemented to mitigate the effects of the potential failure.
• Carefully consider all the risks—e.g., safety, quality, equipment, and resource, as well as efficiency of methods used, actions taken, and contingency planning.
• Consider the major types of design failures: materials, processes, costs.
• Consider the major types of process failures: too much, too little, missing, or wrong.
Once the characteristics that need to be handled with extra care are identified in the FMEA and control plan, this information should be used to develop understandable work instructions for manufacturing, assembly, and verification activities to ensure that potential risk is mitigated effectively and so defects will not be sent downstream or to customers. Where risk is still significant as identified on the FMEA, additional verification activities may need to be implemented from the original plan.
FMEA is a “living” document. When problems arise that were not previously identified, the FMEA and control plan should be revised to include provisions to prevent recurrence. These actions should be deployed as preventive actions for other applicable processes. These activities require resource allocation from top management to provide practitioners with the time needed to complete these important activities.
For additional information on this topic, contact AIAG’s program manager, Dan Reid, at email@example.com.