O Ring capability and measurement - What is the automotive 'norm' for capability studies on O Rings?

[Dave Cx]

All,
Please can someone explain what is the automotive 'norm' for capability studies on O Rings? I have a supplier about to submit PPAPs for several O rings but their proposal doesn't strictly meet the general PPAP requirement. O ring size is a significant characteristic so capability is required.

1. O Rings cannot have individual mould cavity identification so any capability study is of all cavities, arguably each individual cavity could be capable but the spread across all cavities has a high range / not capable? (For context 1 part number is 3mm id moulded on a 360 cavity tool).
2. Producing parts from 1 cavity only (blocking other cavities) & conducting a study on these is not possible as this leaves the tool unbalanced / not production representative.
3. After moulding, the O rings are deburred (frozen then washed), then 100% camera inspected for size / form, there is a high % fall out from this inspection, through this process there's no possibility of maintaining a single moulding shot as '1 lot'.

I'm sure this isn't a new problem just I can't see the pragmatic way through.
Dave

 

[Proud Liberal]

You've already met the requirement. If you have a significant fallout, that is proof that the process is not capable (no Cpk calculation required or optionally back your way in from the fallout data). Since you are already doing 100% inspection, that should satisfy your customer.

 

[Dave Cx]

Hi PL
I did not make this clear but I am the customer and in this case the supplier is reliant on 100% inspection (& hence so are we). So 100% inspection overrides the capability study requirement, our supplier manual does accept 100% inspection in lieu of capability; how would this usually reflected within their PPAP to me?
Dave

 

[Proud Liberal]

It should be documented on the PFMEA, control plan, initial process studies, and noted as an exception on the PSW.