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Answers to questions from webinar #1


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Carl's response to nearly 30 questions posed on the first of three sessions.

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Answers to questions from webinar #1

  1. 1. Questions and Answers from Webinar #1Q1: Should we need to keep target values of RPN as objectives to take actions in FMEA?A1: First of all, there are two different forms of risk in the RPN number: high severity regardless of RPN,and high RPN by itself. Targeting only RPN misses the potential risk of high severity – low RPN issues,which can devastate a company. Some companies choose to provide target values or “thresholds” forRPN, where action is mandated if RPN exceeds the target value. There is no problem with ensuring thatitems with high severity or high RPN values get added review. However, mandating action for RPNabove a threshold has the potential of a numbers game. The best practice is to first ensure that allhigh-severity items are addressed regardless of RPN; and then to address all high-RPN items, beginningwith the highest and continuing until the FMEA team and management is satisfied that risk is reduced toan acceptable level. See section 7.1 “Prioritize Issues for Corrective Action,” pages 163 to 165 in EffectiveFMEAs.Q2: Could you please define failure modes from different context like system, sub-system, andcomponents.A2: “Failure mode” is the manner in which the item or operation potentially fails to meet or deliver theintended function and associated requirements. Depending on the type of FMEA, such as System,Subsystem or Component, the description of the corresponding failure mode will look different.The following is Figure 3.2, page 31 from Effective FMEAs. It shows the progression of Failure Mode andCause from system to subsystem to component, using the example of fictitious bicycle FMEAs.
  2. 2. Q3: Do you include damage effects too? (ex = hose fails and sprays fluid on components)A3: Yes. It is important to trace the effect of the failure mode all the way from the local level (hose) upto the system level (overall system, including the hose). The end effect can be described for both thesystem and the end user. Fluid spray can damage adjacent system components as well as generateunsafe conditions for operators. Reference 7.4 “Effects”, pages 32 to 34 from Effective FMEAs.Q4: How to differentiate between FMEA and FTA (Fault Tree Analysis)?A4: Excerpt from Chapter 14, section 14.2 “FTA and FMEA”, page 317 of Effective FMEAs: “The primary differences between FTA and FMEA include: 1. FTA is a graphical representation of the complex relationships in the system leading to the unwanted event, whereas FMEA is worksheet based. 2. FTA considers the interactions between unwanted events and multiple contributors, such as two or more contributors that each must be present in order for the unwanted event to manifest. FMEA usually considers each contributor separately. 3. FTA has the capability of incorporating the probabilities for each of the contributors and the complex interactions and interrelationships with the top-level unwanted event. FMEA does not usually support the probability calculation of a top-level unwanted event.”Section 14.2.1 “When Should FTA Be Used in Addition to FMEA?” page 317 of Effective FMEAs, providesmore information.Q5: What controls can be put in place during the FMEA creation process to assure the proper level ofdetail?A5: Proper level of detail is important to ensure that the FMEA is complete, but does not become toocumbersome and a waste of time. Good FMEA facilitation keeps the team focused on areas of risk thatlead to root causes and effective corrective actions. FMEA discussion should be limited to areas ofconcern by one of more members of a properly constituted FMEA team, and avoid lengthy discussionson low-risk issues. In other words, the higher the risk the more important and in depth should be thediscussion. Lower risk issues should receive less, but appropriate discussion. For more information,reference pages 231 to 232 of Effective FMEAs.Q6: Do you prefer including items in analysis even if theyre low risk, just to document that youvethought about them?A6: Chapter 4, sections 4.2 “FMEA Project Selection Criteria” and 4.3 “Preliminary Risk Assessment”,pages 58 to 60 of Effective FMEAs, covers how to select FMEA items for analyses. These sectionsintroduce the concept of Preliminary Risk Assessment, in order to narrow down which items will benefitfrom FMEAs. It is not advised to automatically perform FMEA on every subsystem and component in acomplex system, as FMEAs take time and cost money. In addition to performing Preliminary Risk
  3. 3. Assessment, I suggest documenting the selection criteria and assessment that clearly shows which itemsare analyzed, which items are not analyzed, and why.Q7: When selecting a failure identification tool we often choose Fault Tree Analysis because it can catchmulti-point failure. Are there any suggestions on how to cover multi-point failures with FMEA?A7: Usually FTA is the best tool when dealing with failure modes and causes with multiple contributorsand complex interactions. See the answer above regarding FTA and FMEA.Q8: What do you think of FMEA templates for the use in RCM?A8: If by FMEA templates you mean preloaded worksheets of FMEA information for use in RCManalyses, I have concerns. Any time generic or preloaded worksheets are used, there are caveats, suchas the relevance, accuracy or applicability of the information in the template to the specific applicationin the RCM project. They can sometimes be useful as thought-starters, but caution is advised.Q9: How do we share management with HL Output of FMEA from dollars and cents? Off course mgmthas retention deficiency.A9: I will cover this topic on Friday during the Webinar on the subject of Effective FMEA Process.Q10: Do you recommend having a "fixed" FMEA team for an organization? Or is a different teamassembled each time (even for the same system, part, etc.)?A10: I prefer to use guidelines for the representation of FMEA core teams. However, each FMEA isdifferent and guidelines can be modified to fit the needs, risk and timing of individual FMEA projects.Reference section 5.3.4 “Assemble the Correct Team”, pages 93 to 96 of Effective FMEAs.Q11: What are the keys to best describe part function(s)?A11: A “Function” is what the item or process is intended to do, usually to a given standard ofperformance or requirement. In the example of a part, the key is to describe in sufficient detail theprimary functions of the part being analyzed, and include the performance standard. For example, if thepart is a projector lamp, one function of the projector lamp might be “provide XX lumens of light forimage transfer for minimum yy hours of use.”Q12: Are you familiar with the VDA 4.2 standard? If so, what are your thoughts? It looks like a very goodapproach for system FMEAs.A12: VDA 4.2 has a good approach to FMEAs in a very general sense. I prefer to use SAE J1739 as astarting point for FMEAs, and then tailor the worksheet and scales to the unique needs of the companyor organization. For more information, please reference section 5.2.2 “Selecting or Modifying FMEAWorksheets and Scales”, pages 68 to 70, from Effective FMEAs.Q13: Regarding FMEA level of detail; what general rules do you have for keeping the level not too highand not excessively granular?A13: See question/answer #5 above.
  4. 4. Q14: Is there a good rule of thumb on how to estimate the cost of a FMEA? Such as for an electronicsystem, would it be 16 hours per a CCA (8x8" with 4 200 pin BGAs)?A14: Cost of FMEAs is proportional to the amount of time needed by the FMEA team to do a proper jobof the FMEA procedure, and includes the cost of both the analysis and execution. There are manyvariables in determining the time estimate, including system/component complexity, degree of newtechnology, unresolved field issues, supplier involvement, and others. I’ve seen FMEAs take anywherefrom only a few hours (small part, very few changes, no new technology) to many weeks (complexsystem, brand new, unproven new technology). I know of no rule of thumb that has proven the test oftime. FMEA is not merely “filling out a form”, and involves important cross talk and synergy by aproperly constituted team of subject matter experts. Chapter 4 of Effective FMEAs provides informationabout the criteria that impacts a preliminary risk assessment, and from these criteria you can get an ideaof how much time is involved.Q15: I recently retired from the Dept of Defense. Our [component] FMEAs were supposed to bereviewed/updated each year. They [FMEAs] were not. How often should FMEAs be reviewed/updated?A15: Good question. I will show the steps of an effective FMEA process on Webinar #3 (Friday Sept 7th),which includes the feedback loop for updating an FMEA with test and field issues that occur after theinitial FMEA completion. The question about how often can be answered in the following way. I wouldensure the FMEA repository is updated as often as needed so that it can be used for new FMEAs thatbuild off the previous version. I’ll be sure to cover this on the 3rd Webinar.Q16: How does FMEA include or contain a risk assessment of manufacturing process errors, which canbe a significant cause of field failures?A16: A properly done Process FMEA will examine manufacturing process errors and ensure the risk ofmanufacturing errors is reduced to an acceptable level.Q17: Question about setting RPN setting: Are there any pitfalls in setting an RPN threshold based onpast experience? Or do you suggest to always leave the RPN threshold to each FMEA team?A17: Please see the answer to the 1st question above. Also see section “Limitations andAlternatives to Using RPN”, pages 150 to 152 of Effective FMEAs.Q18: Please explain basic difference between SAE ARP5580 and J1739. Why two different standards?A18: A quote from SAE ARP 5580: “Recommended Failure Modes and Effects Analysis (FMEA) Practices For on-Automobile Applications describes the basic procedures for performing a Failure Modes and Effects Analysis (FMEA). It encompasses functional, interface, and detailed FMEA, as well as certain pre-analysis activities (FMEA planning and functional requirements analysis), post-analysis activities (failure latency analysis, FMEA verification, and documentation), and applications to hardware, software, and process design. It is intended for use by organizations whose product development processes use FMEA as a tool for assessing the safety and reliability of system
  5. 5. elements, or as part of their product improvement processes. A separate, Surface Vehicle Recommended Practice, J1739, is intended for use in automobile applications.”ARP 5580 was intended to replace Mil Std 1629a, but as it turns out many companies still use 1629a formilitary applications. I prefer to use SAE J1739. Many non-automotive applications use SAE J1739 withexcellent success. I recommend J1739 as a starting point, unless you are mandated to use a specificstandard. The key is to modify the worksheet and scales to fit your specific application.Q19: Have you seen FMEA applied to Privacy Risks?A19: Please email me with more information about your specific privacy-risk application, and I will beglad to provide my opinion. Carl.Carlson@effectivefmeas.comQ20: I have found a very good use of FMEA to mechanical functions, however to an electronic assemblyis to me very complicated as the potential number of failure modes becomes almost unlimited. How toproperly focus the FMEA to make it efficient and effective for complex electronic productsA20: I have seen many excellent uses of FMEA as applied to electronic/electrical functions, bothhardware and software, large and small. The key is to ensure that the primary functions are welldescribed, and the FMEA procedure is done properly. Be sure to begin with proper FMEA BlockDiagrams and Functional Block Diagrams, as covered in section 5.3.2 of Effective FMEAs. I coverSoftware FMEAs in section 15.4, pages 348 to 356 of Effective FMEAs.Q21: What is the difference between an FMEA and a Fish Bone Diagram?A21: A Fishbone (Ishikawa) Diagram is a graphical representation of the causes of some event. An FMEA,on the other hand is an engineering analysis done by a cross functional team of subject matter expertsthat thoroughly analyzes product designs or manufacturing processes with the objective of finding andcorrecting weaknesses before the product gets into the hands of customers. An FMEA can generate aFishbone Diagram; but a Fishbone Diagram cannot generate an FMEA.Q22: As a plant support engineer for power plants, what resources are available to help determinefailure modes for old equipment (>25 years old) - some vendors may be out of business, loss ofknowledge of SME, etc. (Gene)A22: There is no easy answer to this problem of aging equipment failure rates, where vendors are out ofbusiness and actual field data does not exist. I cover some options in section 5.2.9 “Access to FailureInformation”, pages 76 to 78 of Effective FMEAs. You may also find useful information on the GIDEPwebsite. GIDEP stands for Government-Industry Data Exchange Program.Q23: Do you always create Boundary and Parameter diagrams prior to performing a DFMEA? (Kevin)A23: For System or Design FMEAs I always use FMEA Block Diagrams. I use Parameter Diagrams whenthe item under analysis is a complex system with many system interactions, operating conditions, anddesign parameters, and the team will benefit from seeing these elements visually. Reference section5.3.2.3 “Parameter Diagram (P-Diagram)”, pages 85 to 87 in Effective FMEAs.Q24: Whats the most effective way for determining RPN limits for an FMEA Procedure? I.E. If I have an
  6. 6. RPN limit of 50 how do I know if that RPN is effective for analyzing the products process or designfailure modes. How do I answer the question, is it too high or not high enough? (Chris)A24: Each company must decide what is meant by “reduce risk to an acceptable level.” A high severity –low RPN issue may be higher risk to customers and the company than a low severity high RPN issue.Some companies go so far as to establish risk mitigation strategies for each combination of severity –occurrence – detection. RPN by itself is inadequate for a one-size-fits-all risk metric. Reference section6.2.11.1 “Limitations and Alternatives to Using RPN”, pages 150 to 152 of Effective FMEAs.Q25: got here late - are slides or webinar available to keep up with the series? (Thomas)A25: Please contact Fred Schenkelberg, who will provide the information on webinar slides availability.Q26: How do you decide at what level of indenture to start FMEA?A26: For a new or revised system, I almost always begin with a System FMEA. Then I use Preliminary RiskAssessment to identify which subsystems and components will need Design FMEAs. Preliminary RiskAssessment is fully explained in Chapter 4, section 4.3, pages 59 and 60 of Effective FMEAs.