posted 03 August 2001 02:02 PM               

quote:

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Originally posted by AllenLee:
Could anybody tell me whether we need to conduct SPC control chart to control all of the Special Characteristics?

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Nowhere in QS-9000 is a requirements to use SPC charts. What is required is that a company review the need for statistical techniques during the APQP process (4.20).

I think there is an ever declining view that SPC and statistics are synonimous, they are not. SPC is a specific set of techniques, statistics cover a much larger scale.

Most of us have graphs and charts as part on management review. They are not SPC charts, but they are statistical charts as they contain numbers, trends, actions required etc...

On a more personal level, I believe all special characteristics need some type of control methodology that is determined during the preparation of the FMEA and control plans. They do not have to be SPC, but SPC charts work well in identifying and verifying the process.

ASD...

posted 03 August 2001 07:10 PM               

Please correct me if my understanding is wrong here….. it is a requirement in QS9000 to follow the requirement set forth in the PPAP manual (4.2.4). Although I don’t have a PPAP manual in front of me and if my memory serves me correctly, it is a requirement in the PPAP manual to maintain capability indices of 1.XX on special characteristics.

To achieve a CPK value we must first determine our process is in control. To determine our process is in control we utilize a SPC chart. So in a round about way, it is a requirement to utilize SPC for special characteristics.

posted 04 August 2001 07:15 AM               

In section 1.2.2.9.1 it is set forth more clearly that in that it says we shall determine the level on "initial" process capability. It gives us some different options, but people can read those on their own.

I real world practice we always have a control chart for all special characteristics beginning with PPAP and generally as the process shows ongoing capability and stability we reduce the frequency of the checks, with customer agreement.

posted 05 August 2001 08:30 PM               

But does it mean that we just conduct initial capability study for all SC during the APQP stage; at mass production stage, maybe SPC control chart and Cpk calculation are not required to all SC.

Am i right?

Rgds!

posted 05 August 2001 10:53 PM               

quote:

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Originally posted by AllenLee:
maybe SPC control chart and Cpk calculation are not required to all SC.

Am i right?

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Ultimately it is what you and your customer agree upon. But by the definition of QS9000, you are to maintain and monitor process capability as approved via PPAP. This includes an "appropriate reaction plan" if the process becomes "unstable or non-capable". (4.9.2)

posted 06 August 2001 12:51 AM               

My meaning is that we don't want to control the SC using control chart e.g.: X-bar & R chart. Because we have very high Cpk about 5, so i want to cancel X-bar & R chart control for this SC.

Can it be accepable?

Rgds!

posted 06 August 2001 08:15 AM               

With out knowing your specifics and relations with your customer, the safest advise here is: consult with your customer and see what they have to say. The odds are if you have a capability of 5, they are content with the quality of that characteristic. They may consent to the elimination of monitoring of that characteristic.

QS does state in 4.9.2 “When processes and/or product indicate a high degree of capability (e.g. Cpk/Ppk >= 3), the supplier may revise the Control Plan, as appropriate (see PPAP and Section II).

I would question the elimination of monitoring of any critical or special characteristic. In your situation I would recommend reducing the frequency. If you are testing hourly, consider once a day or even weekly.

Again, in my opinion, the key is to be up front with your customer. Make the changes with them in agreement.

posted 06 August 2001 05:09 PM               

GP-12.doc

ASD...

posted 07 August 2001 08:19 PM               

Once the Control Plan is revised (e.g.: change the characteristic from 'special' to 'normal'); the related FMEA, Work Instruction, PPAP, APQP documents will be affected and updated?

posted 07 August 2001 10:51 PM               

I am slightly confused by the direction of your last question. The sequence of events seems to be a little bit out of order. Normally the designation of a special characteristic is a design control. And if the design is changed and a characteristic is reclassified from a critical to normal, yes… all associated documentation is affected and updated.

I don’t believe that it would be appropriate to change the design based off of a high process capability. A high process capability might justify the reduction in frequency of inspection and henceforth a change in the control plan, but not a reclassification of the characteristic.