<<< Back to Index
This Month's Article >>>

FMEA Corner 
This Month's Theme is FMEA Functions
Next month's theme will be failure modes

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.

 

 

 
func·tion [fuhngk-shuhn, noun]
In an FMEA, a "function" is what the item or process is intended to do, usually to a given standard of performance or requirement. For Design FMEAs, this is the primary purpose or design intent of the item. For Process FMEAs, this is the primary purpose of the manufacturing or assembly operation; wording should consider “Do this [operation] to this [the part] with this [the tooling]” along with any needed requirement. There can be many functions for each item or operation.


!FMEA Tip of the Month

For Design FMEAs, the function statement needs to include the standard of performance. Many FMEA practitioners omit this important element of the function description. For example, an FMEA team might identify one of the primary functions of a power steering pump as “delivers hydraulic power for steering.” However, without including a standard of performance, it becomes more difficult to properly identify the failure modes, and as a result, important failure modes can be missed. A better statement of function would be “Delivers hydraulic power for steering by transforming oil pressure at inlet ([xx] psi) into higher oil pressure at outlet [yy] psi during engine idle speed.” Including the standard of performance in the function statement enables the FMEA team to more easily identify the correct failure modes. For Process FMEAs, the function is usually stated in terms of Do this [operation], to this [part], with this [tooling], with the addition of applicable standard of performance. There can be many functions for each item being analyzed, although the FMEA team should limit function descriptions to the primary functions.

*Beginner’s Problem

In an FMEA, which of the following is true about a “function”? [Show/Hide Answers]

1. A “function” is what the item is intended to do, and can be listed with or without respect to a standard of performance.

2. A “function” is what the item is intended to do, usually to a given standard of performance.

3. There is always one function for each item in an FMEA.

4. The function description in an FMEA must include the consequence or impact on the end user.

**Intermediate Problem

Scenario: You are preparing to lead a series of FMEAs on the all-terrain bicycle project. The “All-Terrain Bicycle Functional/Technical Specifications” includes the following verbiage:

Front suspension
Should be able to absorb forces up to 1000N without reaching the end of the travel distance. Should use a 75mm-travel coil-sprung fork with hydraulic damping for greater adjustability and control. Should withstand g-force acceleration to 3g, above which it is considered abusive usage. The fork shock absorber should have adjustable spring rates and damping. The damper should be oil-filled (not air-compressed).

Color offerings
Grey-black or silver-red with scratch resistant coating.

Frame strength
Should be able to withstand 2x the 95th percentile rider (in terms of weight) on the top part, plus 2000N of force on points of contact with rear and front wheel, 1500N on point of contact with handlebars.

Frame weight
Should be less than 25 pounds (maximum).

Frame material
B1457 premium aluminum. No visible corrosion on frame for 8 years.

Frame diameter
Maximum diameter of frame is 2 inches at down tube, top tube 1 inch, seat tube 0.75 inch, rest of tubes up to 0.5 inches.

Frame welding
Tungsten Inert Gas (TIG) welding.

Gears
ABC 9-speed. Ease of pedaling—should be able to move bicycle with 5Nm torque on first gear.

Rims
Double-walled 26-inch alloy rims should be able to withstand 2x the rider’s weight, plus 3g-force deceleration impact on solid surfaces such as rocks. Each rim should be no more than 10% of bicycle’s total weight.
 
Tubes
Should be designed for nominal pressure of 40 psi (2.8 bars), but should be able to withstand temporary increase of 50% in pressure.

Problem 1: The front suspension has a requirement: “Should withstand g-force acceleration to 3g, above which it is considered abusive.” Should this requirement be part of the Suspension Subsystem Design FMEA, and if so, how would it be used? [Show/Hide Answer]

Problem 2: The gears have a requirement: “Ease of pedaling—should be able to move bicycle with 5 Nm torque on first gear.” Should this requirement be part of the Pedal-sprocket-derailleur Subsystem Design FMEA, and if so, how would it be used? [Show/Hide Answer]

Problem 3: What type of requirement seems to be missing from the All-Terrain Bicycle Functional/Technical Specifications? [Show/Hide Answer]

?Something I’ve always wanted to know about FMEAs

“A prudent question is one-half of wisdom.” Francis Bacon

Beginning next month, and continuing each month, one FMEA question/answer will be highlighted in the “Something I’ve always wanted to know about FMEAs” section. HotWire readers are encouraged to send FMEA questions to Carl.Carlson@EffectiveFMEAs.com. Questions can be on any FMEA topic, with any level of difficulty, from beginner to advanced. Question submitters can either provide name and company, or (if requested) can be kept anonymous. Don’t hesitate to ask any question on the subject of FMEA theory or application.


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.