Your Reliability Engineering Professional Development Site
Carl and Fred discuss the various types of interfaces in electrical and mechanical systems and how they should be included in reliability analyses.
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Can you take into account reliability or durability functions in an FMEA? How can this be done? A reader asks this question, and it is discussed and answered in this FMEA Q and A article.
“A prudent question is one-half of wisdom.”
Francis Bacon
Carl and Fred discussing the importance of understanding and applying failure mechanisms in achieving high reliability.
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Carl and Fred discussing to talk with management about the subject of reliability.
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In this week’s FMEA problems and solutions article, the intermediate problem challenges readers to prioritize a series of RPNs (with their corresponding S, O, and D). In the advanced problem, readers are asked to weigh in on a fictitious debate between advocates of traditional RPN, and advocates of criticality assessment, using only severity and occurrence.
If you haven’t yet read the article titled “Prioritizing risk for corrective actions in an FMEA – Know before you go!“, you can access it by clicking on the link. [Read more…]
Carl and Fred discussing the reasons for performing a Reliability Gap Assessment, and how it fits into the Reliability Plan.
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Carl and Fred discussing a few basic steps necessary to create an effective reliability plan, including setting the goals, understanding the challenges and identifying the key tasks.
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Note from author:
Since this article was originally published, there are subsequent articles in the “Inside FMEA” series that further describe better approaches than RPN to risk prioritization. Here are links:
Is There a Better Way Than RPN?
Risk Prioritization in FMEA – a Summary
Is There a Better Way Than RPN?
Text of the original article:
One of the most important steps in FMEA procedure is prioritizing risk for corrective actions. As soon as Severity, Occurrence, and Detection ratings have been determined for each failure mode and associated cause, the next step in an FMEA is to prioritize the risk and identify which issues need corrective actions. This step has been misapplied more often than any other step in the FMEA process.
“The perfect is the enemy of the good.”
Voltaire
Carl and Fred discussing the primary steps to achieving high reliability.
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Carl and Fred discussing the importance of customer perception from a reliability point of view.
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What if a production worker uses a different cleaning method for an assembly operation than was outlined in the operation work instructions, and the result is customer complaints and field issues. How could this be addressed in a Process FMEA? This question is discussed and answered in this FMEA Q and A article.
“I think that probably the most important thing about our education was that it taught us to question even those things we thought we knew.”
Thabo Mbeki
Can you find this common error in detection ranking in the intermediate problem in this article? In the advanced problem, the topic of an in-service detection scale will challenge the most experienced readers.
Failure modes and their causes can be detected in service, like tire pressure monitors on your vehicle. Is that what is assessed in the Detection column of the FMEA? This article discusses detection risk, including examples, and answers this question.
“There is nothing more deceptive than an obvious fact.”
Arthur Conan Doyle
The Oxford English Dictionary defines “detection” as “the action or process of identifying the presence of something concealed.”
What is the definition of “Detection” in an FMEA?
“Detection” is a ranking number associated with the best control from the list of detection-type controls, based on the criteria from the detection scale. The detection ranking considers the likelihood of detection of the failure mode/cause, according to defined criteria. Detection is a relative ranking within the scope of the specific FMEA and is determined without regard to the severity or likelihood of occurrence. [Read more…]
Ponder this question: Let’s say you are an OEM and assemble parts made by various suppliers. When performing your Process FMEA, do you consider special characteristics for components in your Process FMEA? This question is discussed and answered in this edition of FMEA Q and A.
“The key to wisdom is this – constant and frequent questioning, for by doubting we are led to question, by questioning we arrive at the truth.”
Peter Abelard
I do not introduce special characteristics for components in Process FMEA because we have to consider that the components that we are buying have to be according to drawing specifications and we are not influencing them in our process.
Those special characteristics are treated in the Design FMEA and Control Plan.
Could you tell me your opinion about this?
This is an excellent question.
You are correct that you are not influencing the specifications of a purchased part during your assembly process. In many cases, Process FMEA teams assume that supplier components are in accordance with drawing specifications. However, there are exceptions to this assumption, which I will outline with an example.
Let’s say company A manufactures fuel delivery subassemblies, and they purchase fuel line quick-connects from supplier B. Let’s further say that company A is conducting a Process FMEA on their assembly process for the fuel subassemblies. Here’s the general rule about incoming parts:
Process FMEAs typically assume the design requirements are correct and 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.
With regard to the quick-connect incoming parts from supplier B, company A now has a choice. They can assume the parts they receive from supplier B meet specifications. However, they can make an exception to that assumption. If the quick-connect device is critical to their fuel subassembly and they have reason to believe that the device may not meet requirements, they can consider this exception: incoming parts or materials may have variation and do not necessarily meet engineering requirements. Historical data for quick-connects or fuel sub-assembly risk analysis may indicate this exception. If the fuel subassembly Process FMEA team wishes to make this exception and not assume the incoming quick-connect device meets specifications, they may need to add a step or two to their manufacturing process, or modify existing steps.
Let’s trace this progression from the viewpoint of special characteristics. For a deeper understanding of how special characteristics fit within the broader FMEA quality framework, see FMEA Quality Objective 8: Special Characteristics.
One possible special product characteristic for supplier B’s quick-connect is “inside diameter of the connecting device.” Supplier B would make this a special product characteristic, and identify associated special process characteristic(s) that are needed to control the inside diameter during the quick-connect manufacturing process. As you point out, those special characteristics are treated in the supplier’s DFMEA and Control Plan. The final quick-connect product should meet dimensional and performance specifications before shipping to company A for use in the fuel system assembly. If company A is concerned about this special product characteristic (inside diameter of connecting device), and if they choose to make an exception to the assumptions about this incoming part, they can consider changes to their assembly process to accommodate this exception. Changes might include measuring the inside diameter, or modifying the process controls to detect and accommodate inside diameter variation. They can also recommend action that improves the quality of supplier B’s quick-connect device. In addition, they can request that the design team consider modifications to the fuel subassembly design to be more robust to anticipated variation in quick-connect inside diameter variation.
Failure modes and their causes can be detected in service, like tire pressure monitors on your vehicle. Is that what is assessed in the Detection column of the FMEA? The next article discusses the subject of detection risk, including examples, and answers this question.
Carl and Fred discussing the most important challenges facing reliability engineers.
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