Should we monitor all Significant part Characteristics with SPC? Low Volume CNC

[wslabey]

Should we monitor all Significant part Characteristics with SPC?

BACKGROUND
We are being asked to CNC machine low volume castings for an automotive OEM (it's a service part). PPAP was submitted a year and half ago and the PSW signed off and approved. We've made small batches of the part for the last year and a half. Now the Supplier Tech Assistance Rep is asking for SPC monitoring of all SC's.

If so, what is a good sampling strategy to assure the process is stable and under control?

 

[Wes Bucey]

Should we monitor all Significant part Characteristics with SPC?

BACKGROUND
We are being asked to CNC machining a low volume castings for an automotive OEM (it's a service part). PPAP was submitted a year and half ago and the PSW signed off and approved. We've made small batches of the part for the last year and a half. Now the Supplier Tech Assistance Rep is asking for SPC monitoring of all SC's.

If so, what is a good sampling strategy to assure the process is stable and under control?

At this point, I would reply, "Anything you want - Let's draw up a new contract or an addendum to the original to cover payment for this added requirement."

Under NO circumstances would I do it for free at this point if it was NOT a requirement of the original contract. Even then, the clause may have been waived when they accepted previous batches.

 

[wslabey]

At this point, I would reply, "Anything you want - Let's draw up a new contract or an addendum to the original to cover payment for this added requirement."

Under NO circumstances would I do it for free at this point if it was NOT a requirement of the original contract. Even then, the clause may have been waived when they accepted previous batches.

Wes,

I am livid with this new request. Here is the irony in all this. The STA who signed the PPAP was assigned to perform the Q1 audit. It was during theis Q1 audit that she found this concern (see below for the relevant Q1 clause):

""II.1.4
Where Customer has defined an Engineering Specification (ES), or special characteristics that are the responsibility of the sub-supplier, the sub-supplier must show compliance to the ES or special characteristics in its PPAP submission to the Tier one supplier."

 

[Jim Wynne]

Wes,

I am livid with this new request. Here is the irony in all this. The STA who signed the PPAP was assigned to perform the Q1 audit. It was during theis Q1 audit that she found this concern (see below for the relevant Q1 clause):

""II.1.4
Where Customer has defined an Engineering Specification (ES), or special characteristics that are the responsibility of the sub-supplier, the sub-supplier must show compliance to the ES or special characteristics in its PPAP submission to the Tier one supplier."

I can't see a relationship between the cited requirement and doing ongoing statistical analysis. Did you "show compliance" in the original approved PPAP submission? In this case, "show compliance" could be as simple as providing dimensional verification results. I agree with Wes in his contention that if this extra stuff wasn't documented in the original contract, at least by reference, then let the negotiations begin. I also agree with Wes when he suggests that if there was a requirement in the beginning that the supplier didn't enforce prior to this, it may have the effect of nullifying the requirement, especially if they approved what you were doing in the beginning (PPAP approval includes at least tacit approval of everything in it).

 

[Wes Bucey]

I guess the bottom line is we think the action by STA stinks!

That said, you may have to "escalate" the situation above STA to find a reasonable ear. This is an item which will almost always require intervention by "suits."

 

[D.Scott]

TS doesn't actually require you to do SPC on special characteristics but you are required to "demonstrate conformity to customer requirements for designation (you say this is already defined), documentation and control of special characteristics." 7.2.1.1

The auditor is correct about the Q1 requirement. You will notice the same requirement in the PPAP manual which, as an OEM supplier, you are required to follow. 1.2.2.9.1 states: "the level of initial process capability or performance shall be determined to be acceptable prior to submission for all special characteristics designated by the customer or supplier". Whether it was overlooked or not, the initial process studies were required unless you have a specific customer waiver.

As to the requirement to continue monitoring the process, look at 8.2.3.1 of TS 16949 which states "The orgaization shall maintain manufacturing process capability or performance as specified by the customer part approval process requirements" which in this case is the process capability determined by the Initial Process Studies in PPAP.

As to the sampling strategy, I am afraid I can't offer much. The obvious would be to run a control chart on a characteristic that would give you confidence the process was running as it should. The data collected would demonstrate the capability and stability they are looking for. If you already take a measurement for in-process control, maybe you can use that. I would need to know more about your process and product to make any other comments on what might be appropriate.

Dave

 

[Steve Prevette]

Should we monitor all Significant part Characteristics with SPC?

If so, what is a good sampling strategy to assure the process is stable and under control?

Assuming you want to monitor the characterisics, and ignoring the discussion of the validity of the opinion of the STA, here are some thoughts:

1. Is it data you are collecting anyway? If not, how expensive/ time consuming is it to collect?

2. As far as making the SPC, the cost of that is negligible to the cost of the data. If you have the data, why not plot it on a control chart for the record?

By the way, at Hanford I am on an upward trend again with chart making. Broke the 2,000 mark in December (which was above the UCL), and made 2,126 charts and files in January (up further due to quarterlies). Takes about 15 seconds to update a SPC chart.

 

[wslabey]

Thanks for all the good comments. The OEM needs very few of these service parts. We'll batch run 300 and build an out of fashion just-in-case inventory that's good for 5 year of customer demand. The part is simple, we machine a rough casting and press in a seal.

At PPAP did an initial 5 piece run and inspected 6 ballooned dimensions which the customer signed off on. When we set up and run the part again we do first piece inspection to the ballooned drawing. We didn't quote monitoring the SC's during production with SPC or charting with control charts.

 

[Jim Wynne]

Thanks for all the good comments. The OEM needs very few of these service parts. We'll batch run 300 and build an out of fashion just-in-case inventory that's good for 5 year of customer demand. The part is simple, we machine a rough casting and press in a seal.

At PPAP did an initial 5 piece run and inspected 6 ballooned dimensions which the customer signed off on. When we set up and run the part again we do first piece inspection to the ballooned drawing. We didn't quote monitoring the SC's during production with SPC or charting with control charts.

There could be a commitment by reference in the contract, though. For example, if the contract states that the requirements of customer standard #123 are applicable, then everything that's in #123 is part of the contract. If there's a referenced customer requirement or standard to do control charting for SCs, then you should have been doing it from the git-go, and your customer might be able to enforce the requirement now.

 

[Wes Bucey]

Right! Woulda, coulda, and shoulda are all nice to contemplate as we sit at our computers, but wslabey is on the firing line NOW and needs some workable advice.

("Woulda, coulda, and shoulda" all refer to the point when this whole issue might have been avoided IF it had been caught in Contract Review)

My first advice is to follow Steve Prevette's suggestion and look at what the added cost of compliance to this pissant STAR (Supplier Tech Assistance Rep) and his new (to you) requirement will be for your company. It may well be the cost of compliance at no extra charge to the customer may be worthwhile tuition to protect yourselves next time.

My second advice (if the cost of compliance without compensation is too high) is to involve your suits in negotiating some sort of compromise with the suits who are higher on the totem pole at the STAR's shop, given the circumstances of small volume, etc. Every OEM has a mechanism to make exceptions to its "rules."