Material incoming to the production process reflected in PFMEA

[Martin K.]

Hello all,

I would like to ask for an opinion of anyone, who has any experience with material comming to the production process. My understandind is, that PFMEA always consider all the incoming material (parst from which final product is assembled) as the "OK" one. when we are preparing PFMEA for any of the new processes, we do only failure modes, which can occure on currently considered work place. But some of my oponents in PFMEA team asking to consider possible NG material comming to the work place. but if I have incoming department which is responsible for material testing (visual check, 3D measurement, function test sampling, etc.), then why I have to add wrong material as failure mode and try to think out any C/M?

How can I explain, that in PFMEA there should be only "in station caused" failure modes, not failure modes which can occure before the work station? Well, but only if I am correct in my opinion of course. If I am not, please do not hessitate to tell me why.

Thank You all in advance for any posible comments/help.

Martin K.

 

[Tagin]

but if I have incoming department which is responsible for material testing (visual check, 3D measurement, function test sampling, etc.), then why I have to add wrong material as failure mode and try to think out any C/M?

Does there already exist a PFMEA for this incoming department material testing process? If not, then it would seem to make sense to add it to your current PFMEA as a 'station', since there is no PFMEA to provide assurance that the material incoming to the new process will be good. However, if there is a separate PFMEA already for the material testing process, then I think you could refer your team members to that as assurance that incoming material to your new process will be good (assuming that if the new process places any new requirements on the incoming material that the material testing process PFMEA is updated accordingly).

 

[John Predmore]

When I do a Design FMEA, I consider all component parts to be made to print, because DFMEA is a study of the ability of the design process to detect and correct flaws in the design. However, when I do PFMEA, I consider as failure mechanisms that incoming parts might be oversized, defective or mixed. An incoming inspection department may reduce the occurrence of defective parts, but you may still want to evaluate the possibility of defective parts making it to the operation under analysis.

 

[Martin K.]

hello Mr. Tagin, Mr. Predmore,

yes, PFMEA for incoming dpt. already exists. They have all the testing/sampling documented accordingly to the legal/normative requirements. however I do not see way to include material condition into PFMEA of mine production process. As am describing only failure modes, which may occure on station during assembly (for example "part A inserted to part B - failure modes: not inserted at all, inserted in wrong position, part damaged during insertion, etc.), I do not see any way to add material condition change before its put into the production process.

So if I do have PFMEA for incoming department, there should be no legal reason to keep it in production process PFMEA as well, right?

Thank You both for Your opinion for this problem.

Martin K.

 

[Tagin]

I do not see any way to add material condition change before its put into the production process

I think I understand what you mean: before any station activity occurs there is no way to add an entry to the PFMEA for just the material status. In other words, how can you add a risk entry if there is no function/process to associate it with?

Is this what you mean?

On the other hand, if the material reaches a station and the failure mode is e.g., 'material won't fit in jig (diameter too large)', then that is where you could have an entry for the material not being within spec.

 

[Martin K.]

Hello Mr. Tagin,

"In other words, how can you add a risk entry if there is no function/process to associate it with?" Yes. This is exactly what i mean by my question above. From my point of view operator/machine does not have any chance to change material condition, they can only damage it during insertion, but is operation: operation = insertion, conditions/requirements = correctly inseerted without any damage, failure mode = damaged during insertion, root cause = operator does not follow working instructions for correct handling with inserted component. For PFMEA its easily doable because its operation, right? But for material conditions itself, its different way..

"failure mode is e.g., 'material won't fit in jig (diameter too large)', then that is where you could have an entry for the material not being within spec" Hm, that should do the way, but I am not able to cover all the material diameters/conditions by it I think. If I have material which is marked as S (safety mark) because of flameability possibility, operator/machine does not have any way to check/test/control it during assembly.

in my company there is many years old dogma of keeping material S marking in production documentation and I can not see the way to put it into PFMEA. If nobody has the way to control it in production, i can not add this to PFMEA

I am trying to see the way how to do it or collect all the knowlenge to persuade my coleagues that our company way point of view is not correct from PFMEA side.

Thank You for your comment, its really helpfull to me.

Best regards,

Martin K.

 

[Philip Despard]

Hello Martin & all,
I am really interested in this, as it is a question I have continually asked !
I am involved in assembly and we typically combine multiple received components, e.g. many plastic injection moulded. I had much experience in moulding & realize the risks, but I want to concentrate on the process steps of assembly that I am responsible for !
If we consider that a incoming component is defect, then how & to what level. Where would we stop !, & of course for many incoming components we may not have knowledge of their manufacturing process & risks. Only supplier Quality Eng. may have more knowledge, even that probably limited !, i.e. the supplier controls & level of risk. How far back, Plastic raw material !, financial risk analysis of the supplier, list could go on !,
We also use inhouse moulded parts, but that is covered by moulding FMEA (in our company anyway), so why treat external supply different.

I do not want to shirk from the requirements, but PFMEA form does not ask to risk incoming material (maybe out incoming process, different thing & if we do not follow the headings of the PFMEA form we loose focus of important issues.>
Thanks,
Philip.

 

[John Predmore]

Hello @Philip Despard,
You're right, there has to be a tradeoff how far do you delve into the possibility of poor quality components when doing an assembly FMEA. The approach I would use is limit your analysis to high level failure modes, with focus on deleterious effects on your assembly or assembly operation. One common example is misfed parts (in automatic feeder operations, but parts can get misfed in manual fed systems too). Common failure mechanisms of misfed parts are no part fed to the machine, two parts fed when only one is supposed to be, part fed upside or reversed, loose flash or sprues fed to the nest, or a wrong part number is fed (such as the case of mixed similar looking parts). The high-level cause of Misfed parts could be a supplier quality problem or a feeder adjustment problem or a distracted operator problem, but the effect on your machine of each category of misfed part is the same.

In this high-level analysis, it is not necessary to consider every single dimension of the component, only generic category which leads to common or severe machine faults. What is your process’s ability to prevent or detect misfed parts without allowing a defective assembly to ship, or without breaking the machine or causing excessive downtime?

 

[Jim Wynne]

When doing the PFMEA process, only things that might occur in the current operation should be considered. If there are serial operations, upstream concerns have already been addressed when considering the present operation. The exceptions to this rule are inspection operations wherein by definition the condition of the incoming material is unknown.

 

[Philip Despard]

Hi John,
Mixed / doubled feed, can occur, but that certainly can be our responsibility! to sort / feed better.
Mixed in sprues indicates we have some knowledge of the moulding tool design !, but again, this certainly is supplier issue, , could have contamination with many materials.
I have been involved with automatic vision inspection, & anything can be done (within reason!), but should be driven by the risk. if moulding (or any supply operation) highlight to us there is risk they we can do so.