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PFMEA (Process FMEA) - What is the best approach?

Marc

Captain Nice
Staff member
Admin
#11
You should be working with your customer to evaluate the design of the connector assembly as well as their assembly process/method. Without knowing a number of details it is hard to say what the best course is.

Who designed the connector assembly? Is this a COTS assembly or is it a specific design for a specific customer?

I bring this up because over the years I have worked with a lot of connector assemblies, such as these: AMETEK Sealtron is an expert in glass-to-metal-sealing and is dedicated exclusively to the manufacture of circular hermetically sealed connectors - I worked for them for about a year in the 1980's on MIL SPEC connectors and was responsible for their QPL test program. When you get into the details of a scenario where a connector is wired into a harness, a major factor is stress relief, as is the assembly method/process its self.

Proper stress relief should preclude wires being pulled out of the connectors, so my first thought is there is a design issue of the assembly.

It doesn't sound to me like the failure mode has to do with the connector its self, more likely it is the design of the connector-wire assembly. Of course, their method of connecting the wired connector in their assembly/product can play a significant role.
 

somashekar

Staff member
Super Moderator
#12
Hello,
I understand picture will help a lot, but on my desk computer I don´t have this data. I am sorry.
I believe my question is more general and could be answered even without picture.
Should this failure cause be addressed in DFMEA of connector or PFMEA ? and in PFMEA we only include what could go wrong in our processes and how we control it, is that correct ?
Thank u all.
No DFMEA or PFMEA.
Get back to the inputs including usability and check if the connector type selected meets the applied pull out forces., if it is your selection of the connector type.
I understand that the terminal latch gets bent or cut / or the housing stopper for the pin latch gets cut inside ... at the customer site and the pin slides out, as the retaining is broken.
Prove to yourself and to customer that the connector is good to hold to the suggested pull out force.
 

toniriazor

Starting to get Involved
#13
You should be working with your customer to evaluate the design of the connector assembly as well as their assembly process/method. Without knowing a number of details it is hard to say what the best course is.
....
Hello. It is regular connector for FORD customer. You pointed it out right - the design of connector assembly into car body is far from stress free. There's bending of connector and main branch which creates tension over wires and this is where the problem comes from.
The connector itself is OK and retention results are also OK. I believe the design review and engineering evaluations were poor at the time and now the plant suffers, because of this.

OK it's clear this failure cause should not be in PFMEA since PFMEA is all about process, but what about DFMEA ? or somashekar is right and this should not be included neither in DFMEA ? I just w'd like to have more input why should not be put in these engineering tools.

Many thanks.
 

Marc

Captain Nice
Staff member
Admin
#14
OK - Let me give you an example of what can happen... I was working with a supplier to Harley Davidson a number of years ago. The company was getting numerous complaints about fasteners breaking during assembly. Everything had been reviewed. We believed that the Harley assemblers were the cause, so we made a clandestine visit to the assembly plant and watched from a distance. We saw a number of fasteners break, or threads stripped, and disgarded by the assembly personnel. After about an hour we went to the line. We found that assembly personnel were not going by their work instruction which instructed them to, at every shift start/change, to verify their torque guns. Their torque guns we set at approximately 175% of the prescribed torque. Obviously the fasteners often broke (two piece fastener) or stripped out and/or threads on the part the fastener was used on stipped. The fasteners were not designed to be torqued at the amount the assembler's guns were set at. It essentially was an "employee training" issue (your work instruction says to do this, so you do not have a choice - You follow your work instruction).

After a meeting with Harley middle management in which we pointed out the problem, broken fastener complaints disappeared.

As to your post, my take is it is potentially a dual problem. I am definitely NOT saying that the customer PFMEA is not an issue. It sounds like it is THE issue. It sounds like assemblers are forcing the part. You may to some degree have success in redesiging the wiring assembly to withstand the unanticipated stress being applied (an expense to your company), but if the assemblers are forcing the part you may not be able to redesign it to withstand what I will call "assembler abuse". Parts/assemblies should be designed for "easy" assembly. If force as you describe is necessary for installation, there is a problem. It may be a design issue on your end, it may be a design issue on the part of the customer, and it may be a combination of the two.

In the fastener example above, a change in the design FMEA of the part made no sense. It was, however, added by Harley (customer) as a process FMEA line item. The process FMEA of the fastener supplier was not changed.

In your case it may be that you can come up with a redesign that will fit into the customer's design (look up Design for Assembly...). E.g.: Design for assembly - Wikipedia - This something that requires close communication and interaction with the customer.

This is also a good example of root cause analysis.

:2cents:
 
Last edited:

GRP

Involved In Discussions
#15
Hello everybody,
I decided to put my question here and not to open a new thread. I think it might be relevant.
in PFMEA of a project should it be included a failure cause occuring at our customer which is directly linked to a failure mode which exists in PFMEA?
The company where I work is sending connectors populated with wires and at customer assy line the operators are bending the connectors under certain angle and this creates tension on the already populated wires and then some terminals get pushed out at customer assembly line, not in our processes. Should this failure cause be included in PFMEA ? I think in PFMEA should be included what could go wrong in our processes, not during processes of our customer.
Thank you very much for your answers in advance.
The starting point in the PFMEA analysis -after the process step/function- is the requirement. Is there a requirement in your product´s drawing or technical specification to which the failure mode "pushed terminal" can be attributed? If you have addressed all customer requirements and they are experiencing a failure for which they did not provide input, then it is beyond the scope of your PFMEA.

If they provided a requirement and you have addressed it and your product is in compliance of the requirement, and they still experience the failure, it is also beyond the scope of your PFMEA.

OK it's clear this failure cause should not be in PFMEA since PFMEA is all about process, but what about DFMEA ? or somashekar is right and this should not be included neither in DFMEA ? I just w'd like to have more input why should not be put in these engineering tools.
Whoever designed the connector should have included a line in the DFMEA related to assembly forces and performed DV testing. Most likely this was done, but maybe the stresses or amount of bending was underestimated. As from Marc´s post, the situation will call for investigating the connector design and the assembly process. The design responsible organization may have to update their DFMEA and the customer assembly plant their PFMEA.
 


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