How detailed should I go with “process step”?

[jjley]

Hi, let me give an example.

For example:
My 1st process is Cleaning, 2nd process is coating.
In cleaning, the sub-process are: Pick product from storage >> transport product to line >> place product in cleaning bath >> start cleaning process >> remove product from cleaning bath

In coating, the sub-process are: transport product from storage to line >> put product on mold >> start coating >> remove product from mold

Then in my PFMEA, shall I put “Cleaning” & “Coating” as my process step OR shall I put “pick product”, “transport product”, “place product”, “start cleaning” etc. as my process step?

 

[Miner]

How detailed you get when you list the processes is really up to you, BUT when you start listing the potential failure modes, you must consider each of the detailed sub-processes. Some things to consider:

• Pick product: can you pick the wrong product? If so, can that result in a failure mode?
• Transport product: can you damage or contaminate the product?
• Place product: can you place the product incorrectly (e.g., reversed, upside down, not seated, etc.)?
• Remove product: can you damage the product? As an example, I've molded delicate silicone rubber seals that had to be carefully removed from the mold, or they could tear.

 

[jjley]

Thanks. As I know, the requirement & potential failure mode should be the product characteristic. If I put the process step differently, the process control instead of product characteristics will be at the “requirement” column. Wondering is that acceptable then?

Eg. place product upside down, it will result in wrong coating thickness (product charac.) after the coating process.

If I put process step as coating,
product characteristics/requirement: coating thickness
failure mode: wrong coating thickness
Failure effect: scrap product
failure cause: product upside down due to mold installed wrongly

If I put process step as place product,
Product characteristics/requirement: product position is upright (but product position is actually the process control, it shouldn’t be at this column I guess?)
Failure mode: product upside down (this is not the failure of product characteristics..)
Failure effect: wrong coating thickness lead to scrap product
Failure cause: mold installed wrongly

are they both correct??

Another eg. which makes me more confuse.
If I have add a step before placing product, which is fixing the mold. then,

Product characteristics/requirement: Mold position is upright (it is also process control…)
Failure mode: mold installed upside down (this is also not failure of product characteristics but failure of process…)
Failure effect: product upside down and result in wrong coating thickness
Failure cause: the mold direction is hard to be differentiate

It end up very different…. I’m so confusing, then which is correct?

 

[Miner]

While it is possible that you might duplicate the potential failure modes, consider the following scenario.

• Place product: Potential failure mode = coating on wrong side of product; potential failure cause = loaded part upside down
• Coating: Potential failure mode = insufficient coating; potential failure cause = coating spray set too low

Don't focus on the possibility for duplication. Focus on discovering new potential failure modes.

 

[AndrewK]

in my personal opinion in yours examples more correct 1st one where you say about process step as coating.
Process failure modes should be opposite of product characteristics and req. -so it fits.
Rest of your examples is deep diving to lower hierarchy elements and defining rootcauses of potential causes from 4m

i would suggest to make an structure analysis first- and determine the focus element with which you will work for.
on the top of pyramide will be your final product, on the bottom is yours 4m elements for each process,as it shown

also - define your FmEA scope- will you focus on processes with added value only or whole production chain(on example from handbook transportation for example is not part of analysis as i see- only numbered operations)