DFMEA - Scope - Assumption of good design practice

Hi, I'm new to the forum, although I have been involved with carrying out DFMEAs, on an off, for 20 or so years. Each company and project that I have worked with approaches their DFMEA in a slightly different way, I guess there are subjective to some extent.

My current project has broadened the scope in a way that I am sure is not correct, may I have your guidance please. I always assume that the product has been subjected to the design review process and so good engineering practice is ensured, i.e. the prototype assembles ok. This project is being directed to include failure modes such 'holes mis-aligned, bolt can't be inserted'; I am adamant that this is incorrect with respect to scope, this is suggesting that good desing practice has not been followed. The associated PFMEA should cover the tolerance stack issue.
Am I correct here?

I have been searching for a reference in the manuals for a paragraph that confirms this scope of the DFMEA towards what to assume for the design but unfortunately unsuccessful. The best that I can find is the AIAG HB 1st ed extract below, but I am looking for a clearer directive to the state of the design on which to base the DFMEA.
Please let me know if you know of a reference to this scope and assumptions aspect.

 

Hi Miner,
Thank you for your reply. I know that it doesn't do any harm to include potential failure modes from basic design, although I was unsure of how to describe the boundary of the scope. The 'holes mis-aligned, bolt can't be inserted' potential failure mode implies that the product assembly will be assessed right from the pile of parts. I suppose I should say that this is a system level DFMEA rather than at a component level, and therefore that is why I was assuming that the assembly of the component parts was already accomplished.

Hi Andy,
Thank you for your comments; part made not to print or with the wrong material are out of scope for me too, I appreciate you stating this.

To clarify on aspects such as tolerance analysis of a bolt pattern group, I would expect that it can be assumed that the assembly goes together ok, based on good engineering practice. The assembly is now ready for testing (and simulation prior to and in parallel to testing) and the DFMEA is going to have great influence on the testing regime as higher RPN FMs will need to be sought through rigorous testing. If the second pile of the same parts won't assembly into the second prototype due to a tolerance stack, then is this not more of a PFMEA issue rather than a DFMEA issue?

 

Would it be fair to say that the hole pattern tolerance is within the component level DFMEA, i.e. FM = 'hole tolerance does not always allow assembly of bolts to 'other' part', and that at the assembly (or system) level DFMEA the bolted joint can be assumed to have assembled appropriately (in order to get the system onto test then it is already assembled)?
I don't recall including the operation of assembling the system as a test within Current Control. If the hole pattern tolerance meant that the assembly looked ok but during system operation (testing) the skewed bolts tight in the holes due to 'designed' out of position had caused the gasket joint to leak then this is what I feel we are trying to identify. I don't see how or why we need the DFMEA to predict that we can't assembly the pile of parts in the BoM.

Is there a paragraph in any of the manuals that illustrates the scope of a DFMEA with respect to machine assembly?
Is there a list of typical failure modes that includes aspects that apply to the machine assembly operation (I want to learn, to be convinced of a different point of view but I don't find references for these aspects)?
Does a PFMEA include the operations that assemble the component parts into an assembly?

 

Hi Miner,
Thank you for your further guidance. I like the diagram showing the interconnections between FMEAs; this is helping me.
Do you know of any online training or reference material in this realm of interacting FMEAs?

 

Hi Miner,
That diagram is real high value, thank you so much, I feel like my standpoint is shifting.
Where it says ‘provide dimensional control’ under ‘upper frame’, do you interpret that as meaning provide the correct frame geometry to work well as a bicycle, (handle bars, seat, crank in good relative positions to perform well as a bicycle) or interpreted as the upper frame needs to be 21.1” long to fit in the gap between the other members where that gap is 21.1”?
This is where I say that good engineering practice and a ‘design review for drawing approval’ ensures that the member fits the gap. This was my original understanding but we’re getting to the essence of what I wish to understand properly and clearly. I’m a somewhat binary perhaps but once I buy into a set of rules, then I will endeavour to apply them.