Definition Potential Failure Mode Definition and How to identify Failure Modes?

N

naveenattri

#1
I want to know the defination of term potenial failure mode. and
how we can identify the 'potential failure mode'?

In my case while performing PFMEA we observed that our part is having interface with other component and at each stage of process we are either generating or controlling the part dimensions.

Now if this dimensions goes out of tolerence that is considered as failure mode and this non confernmce may have severe effect (if we considerd the worst impact ) upto the ranking of 8 and 9 . During discussions we developed that in some cases its diificult to develop the non conformance upto this level while manufacturing .

so we are in confusion of what to be set as rule for term potential and is there any thumb rule or process to develop the potentail failure modes ?
 
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Al Rosen

Staff member
Super Moderator
#2
Re: Please Define Potential Failure Mode

I want to know the defination of term potenial failure mode. and
how we can identify the 'potential failure mode'?

In my case while performing PFMEA we observed that our part is having interface with other component and at each stage of process we are either generating or controlling the part dimensions.

Now if this dimensions goes out of tolerence that is considered as failure mode and this non confernmce may have severe effect (if we considerd the worst impact ) upto the ranking of 8 and 9 . During discussions we developed that in some cases its diificult to develop the non conformance upto this level while manufacturing .

so we are in confusion of what to be set as rule for term potential and is there any thumb rule or process to develop the potentail failure modes ?
  1. Possible, as opposed to actual: the potential uses of nuclear energy.
  2. Capable of being but not yet in existence; latent: a potential problem.
  3. Capable of being or becoming: a potential danger to safety.
 

Ajit Basrur

Staff member
Admin
#3
Re: Please Define Potential Failure Mode

Naveen, welcome to the Cove

Failure modes and effects analysis (FMEA) is a step-by-step approach for identifying all possible failures in a design, a manufacturing or assembly process, or a product or service.

“Failure modes” means the ways, or modes, in which something might fail. Failures are any errors or defects, especially ones that affect the customer, and can be potential or actual.

FMEAs should always be done whenever failures would mean potential harm of the end item being designed and therefore in the example that you cited, it could be a part of the PFMEA (Process FMEA)

Process FMEA focuses on manufacturing and assembly processes. Refer to this website for more info - http://www.npd-solutions.com/fmea.html
 

Stijloor

Staff member
Super Moderator
#4
Re: Please Define Potential Failure Mode

I want to know the defination of term potenial failure mode. and how we can identify the 'potential failure mode'?
Hello naveenattri,

I use the AIAG FMEA manual as my reference here...

Definition: Potential failure mode is defined as the manner in which the process could potentially fail to meet the process requirements and/or design intent as decribed in the process function/requirements column. (Page 39)

So, when performing a Process FMEA, a failure mode can be a process failure and/or a product failure.

A good technique to help you identify failure modes is asking:
  • How can the process fail to meet requirements?
  • How can the part fail to meet requirements?
  • Regardless of the engineering specifications, what would a customer (end user, subsequent operations, or service) consider objectionable?
Start by comparing similar processes and reviewing customer (end user and subsequent operation) claims relating to similar components. In addition, a knowledge of the design intent is necessary. (Page 41.)


The actual assembly drawing and access to historical part/assembly information will be very helpful.

Let us know if this was of help to you. If not please come back with more questions.

Stijloor.
 
D

David DeLong

#5
Re: Please Define Potential Failure Mode

Stijloor:

There is a lot of confusion over failure modes in a Process FMEA mixing a potential cause with a potential failure mode.

You stated that it could be both a process or a product but I respectfully disagree.

One must look at the particular process step and state what is expected to occur to the product at that step. Some people might say it is the value added at the process step.

We might be trying to punch 10 holes and we only punch 9. That is a failure mode.

The potential cause could be a number of things in the process. It could be a broken punch or the die might have been made without the provision for the 10 holes. I try to keep the potential causes down to no more than 3.

Again, as I see it, the potential cause is something negative to the product at that process step. It did not meet a requirement of some sort. The potential cause of that failure is in the process.
 

Stijloor

Staff member
Super Moderator
#6
Re: Please Define Potential Failure Mode

Stijloor:

There is a lot of confusion over failure modes in a Process FMEA mixing a potential cause with a potential failure mode.
Confusion? I agree. But...I did not talk about causes. All I did was clarifying Failure Modes and how to identify them.

You stated that it could be both a process or a product but I respectfully disagree.
That's fine. I stand by my (and AIAG's FMEA) opinion that a failure mode can be both process and product at that step of the operation.

One must look at the particular process step and state what is expected to occur to the product at that step. Some people might say it is the value added at the process step.
Absolutely!

We might be trying to punch 10 holes and we only punch 9. That is a failure mode.
Yes! Now we have a process failure.

The potential cause could be a number of things in the process. It could be a broken punch or the die might have been made without the provision for the 10 holes. I try to keep the potential causes down to no more than 3.
I did not raise "causes", but since you bring it up. I do a thorough (potential) root cause analysis to find out. It may be 3 causes it may be more. Who knows? Why limit the options? Actions required will be prioritized anyway.

Again, as I see it, the potential cause is something negative to the product at that process step. It did not meet a requirement of some sort. The potential cause of that failure is in the process.
David, when I consult/train FMEA, my main intent is to make sure that my Clients/Students end up with a solid FMEA, a list of actions and commitments + due dates, hopefully contributing to a more robust design and or process. I am obligated to introduce and teach commonly accepted definitions and practices that are recognized in the industries that I serve. You and I and perhaps others can engage in intellectual and philosophical discussions (as often happens here, but that's OK) about terminology and approaches, but in the end, what counts is what works well and what works for my Client.

Thank you David. I really appreciate your contributions here at The Cove.

Stijloor.
 
D

David DeLong

#7
Re: Please Define Potential Failure Mode

Stijloor:

The reason I try to keep the causes to no more than 3 is the fact that your FMEA can become really large. Let's say someone stated a potential cause was "Martians did it". The occurence rating would be say a 1. Would I keep this in my process FMEA? No, I would discard it. The number keeping no more than 3 is not solid but not too many have more than 3 potential causes with occurence rating over 5 or 6.

Here is an example that I have used in the past on describing potential failure modes and causes.

Let's say the last operation was packing and the Packer was to place a foam wrap around the product so that the edges do not touch during shipping. The Customer opens up the package and observes chipped paint on the corners of the product.

I would say that the potential failure mode here is chipped paint (that is what the Customer views) with 1 potential cause could be that the wrapping was not completely around each product.

I was most interested in a process failure as being a potential failure mode. Could you please give me an example?

Thanks
 

Stijloor

Staff member
Super Moderator
#8
Re: Please Define Potential Failure Mode

Stijloor:

The reason I try to keep the causes to no more than 3 is the fact that your FMEA can become really large. Let's say someone stated a potential cause was "Martians did it". The occurence rating would be say a 1. Would I keep this in my process FMEA? No, I would discard it. The number keeping no more than 3 is not solid but not too many have more than 3 potential causes with occurence rating over 5 or 6.

Here is an example that I have used in the past on describing potential failure modes and causes.

Let's say the last operation was packing and the Packer was to place a foam wrap around the product so that the edges do not touch during shipping. The Customer opens up the package and observes chipped paint on the corners of the product.

I would say that the potential failure mode here is chipped paint (that is what the Customer views) with 1 potential cause could be that the wrapping was not completely around each product.

I was most interested in a process failure as being a potential failure mode. Could you please give me an example?

Thanks
David,

Allow me to use your example.
  • Process step: Wrap two layers of foam around the entire product.
  • Potential failure mode: Foam is not entirely wrapped around the product.
  • Effect of failure: Chipped paint on product, dissatisfied customer.
    You see? The failure mode is not chipped paint. Chipped paint is the effect of the failure mode noticed by the customer.
  • Possible cause: Packer fatigue, etc.
One of the challenges in FMEA (Design and Process) is not to mix up failure modes, effects of failure, and causes. Your focal point must always be the process. What happens as a result of the failure mode is the effect.

I will attach a few slides that clarify this concept.

Stijloor.
 

Attachments

P

Pudge 72

#9
Re: Please Define Potential Failure Mode

I think that I can understand what is being said here in regards to process failure mode -

Let's say that you are a Widget Maker that makes individual components and you have a Maintenance Process for your Widget Making Tool. After making 100K parts, your Widget Making Tool is supposed to get sharpened, but it doesn't - it goes back on the shelf.

Now, the next time you go to get the Widget Making Tool to run the product, low and behold, you can't because it has not been properly sharpened - remember, the Widget that you are making has let's say 150 edges each with a potential for a burr - I ceratinly am not listing every one of those as a potential failure mode, nor am I listing every dimension on the part as a failure mode.
The failure here (and the easiest way to address the problem) is to say that as a whole - the Maintenance process itself within the manufacture of the component has failed. With a good Root Cause Investigation you should be able to determine where exactly in the maintenance process the failure occured, but, the FMEA has given you the heads up as to where to start looking. Your current control would be your Maintenance Procedure ; the Process Function that this area may addressed in could be something like Set-Up of Widget Making Machine ; the actual Failure Mode would be worded as Improper Tool Maintenance or Maintenance Process.
I have found that this method is quite successful to use during the FMEA and my customers love it. I do an FMEA for every component that we manufacture - within the manufacture of any component, you have potential failure modes that can encompass items that relate only to that particular product that you are making, as well as processes that cover a wide span or family of parts or products - all of these must be addressed in the FMEA in some form or another if they can interact in a manner that would pose a critical risk.
 
D

David DeLong

#10
Re: Please Define Potential Failure Mode

Stijloor:

Here is how perceived my example.

Customer opens up a box and finds the paint is chipped on the product. That is the failure mode as I see it. The result of the failure mode is an unhappy Customer who may be discouraged from purchasing more products from the same manufacturer. Does the customer know that the parts are to be fully wrapped? No, I don't think so. Would a customer complain to the manufacturer that the parts where not fully wrapped? I don't think so.

I have always looked at the potential failure mode from a Customer perspective whether the customer is the next operation in the plant or the consumer as in this situation. The failure mode is a product characteristic that has failed to meet their expectations.

The potential cause of this failure could be the wrapping and then we could use the 5 whys or some other method to obtain a core cause(s).

I appreciate this type of discussion.
 
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