This Month's Theme is Pugh
Analysis (also called Decision Matrix Method)
Next month's theme will be "legal guidelines for FMEAs"
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@EffectiveFMEAs.com, and your contact information will be kept anonymous. All questions will be answered, even if they are not featured in the FMEA Corner.
"Once you make a decision, the universe conspires to make it happen." - Ralph Waldo Emerson
decision [di-si-zhuhn, noun]
The Oxford English Dictionary defines "decision" as "a conclusion or resolution reached after consideration."
matrix [may-triks, adjective]
The Oxford English Dictionary defines "matrix" as "a rectangular array of quantities or expressions in rows and columns that is treated as a single entity and manipulated according to particular rules."
What is a Pugh Analysis (Decision Matrix Method)?
A Pugh Analysis is a decision matrix where alternatives or solutions are listed on one axis, and evaluation criteria are listed on the other axis. The objective is to evaluate and prioritize the alternatives or solutions. The team first establishes and weights the evaluation criteria and then evaluates each option against those criteria.
Pugh Analysis was invented by Stuart Pugh, a professor from the University of Strathclyde, in Glasgow, Scotland.
When is Pugh Analysis done in an FMEA?
There are times when an FMEA facilitator has difficulty arriving at consensus with the FMEA team. This most often happens when there are two or more competing ideas or solutions and members of the team feel strongly about their personal idea or solution. One tool that can be used to solve this problem is Pugh Analysis.
How is Pugh Analysis performed?
The steps of a Pugh Analysis are:
- Document the short list of ideas or alternatives that are being evaluated.
- Develop the list of criteria that will be used to evaluate alternatives.
- Assign a relative weight to each criterion based on how important that criterion is to the subject being evaluated.
- Using a simple matrix, list the evaluation criteria on the left and the alternatives across the top.
- Establish a baseline, which may be one of the alternatives or some other solution or alternative the team agrees is a baseline.
- For each of the criteria, evaluate each of the alternatives against the baseline, using scores of worse (-1), same (0), or better (+1).
- Multiply each rating by the criterion weighting. Sum the results and identify the alternative with the highest score.
- If one of the alternatives has not emerged as the clear best idea with team consensus, look for a hybrid idea that captures the best features of the competing alternatives, and rescore.
What is an example of Pugh Analysis?
This example is taken from a fictitious Design FMEA for an
all-terrain bicycle brake cable. One of the failure modes being analyzed
is "cable binds" and a cause is "inadequate or wrong lubrication between
cable and sheath." The team is working on finding the best solution for
this cause (recommended action), and has narrowed down to two possible
lubricants. The first alternative is a lubricant gel that is lower cost
easier to maintain, but has less performance over temperature and
humidity extremes, and provides slightly less friction reduction. The
supplier has an excellent record of quality. The second alternative is a
high performance liquid lubricant that provides better friction
reduction over a wide variety of operating extremes, but is harder to
apply and costlier, and the supplier has a spotty quality record. For the
purposes of the Pugh Analysis, the current lubricant is called
"baseline." As can be seen from the decision matrix, the gel lubricant
slightly outperformed the liquid lubricant. The team looked for a hybrid
solution and found a supplier for the liquid lubricant with a better
quality record that was easier to apply. The hybrid column shows the
results and the decision was made.
The following is an illustration of this example, from chapter 10 of Effective FMEAs.
How can Xfmea support Pugh Analysis?
Below is a screenshot from Xfmea. It shows the FMEA Hierarchy view for an excerpt of a fictitious Brake Cable Design FMEA. In this example, the FMEA team is working on actions for the cause, "Inadequate or wrong lubrication between cable and sheath." They decide to do a Pugh Analysis.
Once the Pugh Analysis is completed, it can be attached to the corresponding recommended action in the Xfmea dialog box. Note the "+" sign just to the left of the recommended action entry.
Of course, the results from the Pugh Analysis will need additional recommended actions.
When you have competing ideas in an FMEA meeting, first use the facilitation skills outlined in FMEA Corner Issue 192 "Essential FMEA Facilitation Skills." Many competing ideas can be resolved with good facilitation. However, if the use of these tools does not resolve the issue, consider using Pugh Analysis. Above all, it is important that the FMEA team be brought to consensus on the most effective solutions to reduce risk.
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@EffectiveFMEAs.com.
Our company makes a subassembly with about 10 components.
In general, for effective DFMEA, do you recommend listing all of the components (almost duplicating bill of material), or rather entering in the DFMEA the interfaces between components or both?
Carl: Thank you for your question. There are a few decisions you will need to make when applying Design FMEA procedure to a product, such as your subassembly. The first decision is which FMEAs to do. In most cases, you will begin with a DFMEA at the subassembly level. You will also need to decide whether or not to do FMEAs at the component level, and how to address interfaces, such as between two of the subassembly components.
The best way to begin is with an FMEA Block Diagram. I’ve attached an example for a fictitious Bicycle Hand Brake. As you can see, this FMEA Block Diagram shows the subsystem (hand brake), the components (such as brake pad and brake caliper) and the interfaces (such as bolt between brake caliper and brake pad).
Hand Brake subsystem interfaces (such as brake pad to brake caliper interface) can be addressed in FMEA procedure in one of two ways:
- They can be included as functions in the higher level Hand Brake DFMEA (example: "Interface: pad to caliper - provides secure connection of pad to caliper")
- They can be listed in the bill of materials as lower-level items, A) brake pad, B) brake caliper, and C) Interface – brake pad to brake caliper. Item C) receives its own mini DFMEA.
All of this is covered in chapters 5 and 6 of my book, Effective FMEAs. The key is to do a proper FMEA Block Diagram, and to be sure that all important interfaces are addressed by either 1) or 2) above.
About the Author
Carl S. Carlson is a consultant and instructor in the areas of FMEA, reliability program planning and other reliability engineering disciplines. He has 35 years of experience in reliability testing, engineering and management positions, and is currently supporting clients from a wide variety of industries, including clients of HBM Prenscia. Previously, 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.
Selected material for FMEA Corner articles 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. Carl Carlson can be reached at email@example.com.