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FMEA Corner 
This Month's Theme is Functional Block Diagrams
Next month's theme will be interface matrix

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.



func·tion·al [fuhngk-shuh-nl, adjective]
The Oxford English Dictionary defines "functional" as "Of or having a special activity, purpose, or task; relating to the way in which something works or operates."

di·a·gram [dai-uh-gram, noun]
The Oxford English Dictionary defines "diagram" as "A simplified drawing showing the appearance, structure, or workings of something; a schematic representation."

What is a Functional Block Diagram?

In chapter 5 of Effective FMEAs, I cover four diagrams that can help make the scope of a System or Design FMEA visible: FMEA Block Diagram, Parameter Diagram, Functional Block Diagram and FMEA Interface Matrix. Each has its own unique contribution to the FMEA application. Not all of these are required, so it is important to know when to use the various diagram tools. From the book:

A Functional Block Diagram is a visual tool to describe the operation, interrelationships and interdependencies of the functions of a system or equipment. By making the primary functions of the equipment visible, it allows the FMEA team members to agree on how the system works and identify the beginning and end of system or equipment operation. It is usually generated before the formal FMEA team meetings start, and is agreed upon by the FMEA team. Each primary (high level) function is placed in a "block" and visually laid out in the sequence performed. Inputs and outputs are added for clarity.

When is a Functional Block Diagram used?

Not every item being analyzed with an FMEA will benefit from a Functional Block Diagram. It is best used at a system or subsystem level in which there are many functional steps in system operation, and the team believes that making the functions visible will aid the FMEA application.

What does a Functional Block Diagram look like?

The following is an example of a Functional Block Diagram.

Functional Block Diagram

How is a Functional Block Diagram used in an FMEA?

The functional descriptions in the Functional Block Diagram are inputs to the Function column in the FMEA. Care should be taken to include the standard of performance as part of the function description in the Function column of the FMEA. (For more information on functions, refer to the October 2013 FMEA Corner.)

Does Xfmea support Functional Block Diagrams?

Xfmea easily attaches any document or diagram to the item being analyzed.

  1. Locate the item in the System Hierarchy.

System Hierarchy

  1. Choose System Hierarchy > Current Item > Attachments, then click Add.

Add icon

  1. Select the type of attachment (such as embedded file, file link or URL), then enter the Address, Name and Description (optional).

Completed attachment

  1. A paperclip icon will show up next to the item in the Attachment column.
  2. System Hierarchy with attachment


Always begin FMEA preparation with an FMEA Block Diagram (which identifies the boundaries of the FMEA, interfaces between items and other information relevant to the scope of the analysis). Also consider using a Functional Block Diagram when there are many functional steps in the system operation and the team believes that making the functions visible will help in the FMEA application.

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

A HotWire reader submitted the following questions to Carl Carlson. To submit your own question about any aspect of FMEA theory or application, e-mail Carl at Carl.Carlson@EffectiveFMEAs.com. (All questions and responses will be kept anonymous.)

I have three questions, if you can help.

1. When is the best moment in the time line to do a PFMEA review in order to still have some time for improvements?

Carl: To answer this question, I'll begin with the overall timing for PFMEAs. PFMEAs should be completed (good quality) by the manufacturing process freeze date for the given part. This means you need to review the PFMEA well enough in advance of the manufacturing freeze date in order to leave time for changes.

2. What would be the minimum acceptable individual rating for the 10 FMEA quality objectives (after improvement)? (Would minimum 3 for each be reasonable?

Carl: First, to be sure we are on the same page, refer to the March 2016 FMEA Corner article on FMEA quality audits. As stated in the article, the focus of an FMEA audit is on improving the FMEA process, not on the person or team doing the FMEA.

I’ll reply to your question by assuming that the reviewer is rating each quality objective on a scale of 1 to 3, where a 1 means the objective is not met, and 3 means the objective is fully in place. Interpreting your question this way, I think you are asking if the only acceptable FMEA quality is where each quality objective is fully in place. My answer is that the best process is to assess the current FMEA quality and work to improve the FMEA process. The objective is for FMEAs to meet the quality objectives. Most companies do not meet these quality objectives right away and have to work over time to improve the quality of FMEAs.

If you are using FMEA quality objectives to evaluate supplier FMEAs, I would answer that for critical supplier parts, their FMEAs should fully meet the quality objectives. This means they may have to continue working on their FMEA until the objectives are met.

3. What would be the minimum acceptable overall percentage for the 10-quality-objectives-audit (after improvement)?

Carl: To answer this question, I again refer to the focus on FMEA quality audits: improving the FMEA process. Each audit should note any shortcomings to the FMEA quality objectives, and identify actions to improve the FMEA process. Over time, the company will achieve higher quality FMEAs.

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 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.

Effective FMEAsSelected 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 carl.carlson@effectivefmeas.com.