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FMEA Corner 
This Month's Theme is Ground Rules and Assumptions
Next month's theme will be "gathering information"

Every month in FMEA Corner, join Carl Carlson, a noted expert in the field of FMEAs and facilitation, as he addresses a different FMEA theme (based on his book Effective FMEAs) and also answers your questions.

Questions and answers are a great way to learn about FMEAs, for both experienced and less experienced FMEA practitioners. Please feel free to ask any question about any aspect of FMEAs. Send your questions to Carl.Carlson@ReliaSoft.com, and your contact information will be kept anonymous. All questions will be answered, even if they are not featured in the FMEA Corner.

 

 

 
ground rule [grownd rool, noun]
The Oxford English Dictionary defines "ground rule" as "a basic rule about what should be done in a particular situation, event etc."

 
as·sump·tion [uh-suhmp-shuhn, noun]
The Merriam-Webster Dictionary defines "assumption" as "a fact or statement (as a proposition, axiom, postulate, or notion) taken for granted."

Establish ground rules and assumptions

"Your assumptions are your windows on the world. Scrub them off every once in a while, or the light won't come in." ― Isaac Asimov

Before beginning an FMEA, the team should discuss (and document) the specific ground rules for how it will be performed and the underlying assumptions of the analysis. Some of these guidelines may have been determined previously by the department's standard practices for FMEA and some may be specific to the particular analysis project.

Ground rules are important so the team can move through the analysis in an effective manner, using the least amount of in-meeting time.

Identifying the underlying assumptions is one of the most critical steps in FMEA preparation. FMEA is about analyzing failures, and what constitutes a failure in a given analysis depends on certain assumptions, as covered below.

For Design FMEAs

A Design FMEA focuses on design-related issues emphasizing how the design can be improved to ensure that product-related risk is low during the useful life of the equipment. This includes any potential failure modes and causes that can occur during the manufacturing or assembly process, which are the result of the design. The team may choose to mitigate such failure modes (for example: error-proofing, design-for-assembly, etc.), and these recommendations should be placed in the recommended actions column.

A Design FMEA usually assumes the product will be manufactured within engineering specifications. In addition, the Design FMEA team may wish to consider an exception: the part design may include a deficiency that could cause unacceptable variation in the manufacturing or assembly process.

For Process FMEAs

A Process FMEA focuses on process-related issues for the manufacturing or assembly process, with emphasis on how the manufacturing process can be improved to ensure that process-related risk is low. The team may identify design opportunities to eliminate or reduce the occurrence of process failure modes, and these should be placed in the recommended actions column of the PFMEA. An example is a design change that eliminates the possibility of operator misassembling a part.

Process FMEAs typically assume incoming parts and materials to an operation meet design intent. In addition, the PFMEA team may wish to consider an exception when historical data indicates incoming part quality issues: incoming parts or materials may have variation and do not necessarily meet engineering requirements.

Example of ground rules and assumptions the FMEA team may consider


!FMEA Tip of the Month

Ground rules and assumptions should be written down and agreed upon by the FMEA team before commencing the analysis. They should be electronically attached to the FMEA, so there can be no question as to what assumptions the team is using throughout the analysis.

 In the Xfmea, RCM++ and RBI software tools, the ground rules and assumptions are included in the Analysis Plan.

Xfmea Analysis Plan Window

*Problem

The ABC lawn mower company designs a residential mower to be able to operate safely on ground slopes up to 30 degrees without tipping over. In other words, the operating profile is anywhere between 0 and 30 degrees. However, it is possible for a customer to make a mistake and use the lawn mower on a steeper slope, say 45 degrees, and subsequently the mower can tip over with potential injury to the user. Is this "tipping over" a system failure? Should the FMEA team ignore this potential failure because it occurs outside the specified operating profile? What should be the assumption that the FMEA team makes regarding this type of potential abuse by customers?  [Show/Hide Answer]

?Something I’ve always wanted to know about FMEAs
The important thing is not to stop questioning. - Albert Einstein

A reader submitted the following question to Carl Carlson. To submit your own question about any aspect of FMEA theory or application, e-mail Carl at Carl.Carlson@ReliaSoft.com.

Our production process is running according to specifications, standards, etc., but we have a problem related to design. Because of this design problem, we could have a failure with our product. We believe a design change is needed (add material) in order to prevent the product failure. My question is this: is there something that I should introduce in P-FMEA if the failure cause is related to design? We have that failure in P-FMEA but with causes related to the process, not design. We implement a cost reduction on the product and we decrease the material quantity (the product is not affected). Also for this, should I update something in P-FMEA?

Carl: Regarding your question about design-related problems that come up during a process FMEA, let me begin with assumptions. The following is from chapter 5 of my book:

A Process FMEA focuses on process-related issues for the manufacturing or assembly process, with emphasis on how the manufacturing process can be improved to ensure that process related risk is low. The team may identify design opportunities to eliminate or reduce the occurrence of process failure modes, and these should be placed in the recommended actions column of the PFMEA. An example is a design change that eliminates the possibility of operator misassembling a part.

Process FMEAs typically assume incoming parts and materials to an operation meet design intent. In addition, the PFMEA team may wish to consider an exception when historical data indicates incoming part quality issues: incoming parts or materials may have variation and do not necessarily meet engineering requirements.

For design FMEAs, the cause is the design deficiency that results in the failure mode. For process FMEAs, the cause is the manufacturing or assembly deficiency (or source of variation) that results in the failure mode. However, if the process team is aware that there is a design deficiency, two strategies can be used. The first strategy is to improve the manufacturing process in order to make it robust to the design deficiency. In other words, the manufacturing process is modified to be able to produce the product to specifications regardless of the design deficiency. The second strategy is to make note of the anticipated design problem and request it be addressed with a design FMEA or other design solution. Although this second strategy is not the usual focus, if the process FMEA team believes the product has a design deficiency that is outside the scope of the process FMEA, I would rather they take action to communicate the issue to the design team and request resolution, than allow the product to result in field failures.


About the Author

Carl S. CarlsonCarl S. Carlson is a consultant and instructor in the areas of FMEA, reliability program planning and other reliability engineering disciplines. He has 30 years of experience in reliability testing, engineering and management positions, and is currently supporting clients of ReliaSoft Corporation with reliability and FMEA training and consulting. Previous to ReliaSoft, he worked at General Motors, most recently senior manager for the Advanced Reliability Group. His responsibilities included FMEAs for North American operations, developing and implementing advanced reliability methods and managing teams of reliability engineers. Previous to General Motors, he worked as a Research and Development Engineer for Litton Systems, Inertial Navigation Division. Mr. Carlson co-chaired the cross-industry team that developed the commercial FMEA standard (SAE J1739, 2002 version), participated in the development of SAE JA 1000/1 Reliability Program Standard Implementation Guide, served for five years as Vice Chair for the SAE's G-11 Reliability Division and was a four-year member of the Reliability and Maintainability Symposium (RAMS) Advisory Board. He holds a B.S. in Mechanical Engineering from the University of Michigan and completed the 2-course Reliability Engineering sequence from the University of Maryland's Masters in Reliability Engineering program. He is a Senior Member of ASQ and a Certified Reliability Engineer.

Effective FMEAsMaterial for the FMEA tips, problems and solutions is excerpted from the book Effective FMEAs, published by John Wiley & Sons, ©2012. Information about the book Effective FMEAs, along with useful FMEA aids, links and checklists can be found on www.effectivefmeas.com.

 
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