Is SPC Required on ALL Special Characteristics?

[AllenLee]

SC Vs SPC

Could anybody tell me whether we need to conduct SPC control chart to control all of the Special Characteristics?

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Allen Lee

 

[Al Dyer]

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

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...

[This message has been edited by Al Dyer (edited 03 August 2001).]

 

[AJLenarz]

Al –

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.

I would be interested in hearing other takes on this….

 

[Al Dyer]

You are correct, that is why I limited the scope of my answer to the QS-9000 manual. Per the PPAP manual we shall perform "initial" capability studies "if applicable" (1.2.2.9.2). There are alot of notes attached to the section on process studies.

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.

ASD...

 

[AllenLee]

Thank you all for your inputs.

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!

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Allen Lee

 

[AJLenarz]

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

Am i right?

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)

The question I ask is “how can you monitor process capability or process stability if you don't do some form of SPC”on these special characteristics?

 

[AllenLee]

Thanks you AJLenarz.

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!

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Allen Lee

 

[AJLenarz]

Allen Lee –

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.

I hope this helps. Any other opinions?

 

[Al Dyer]

For those slaves to G.M. you might want to review the GP-12 procedure in the GM procedure folder in the FTP site of the forum.

GP-12.doc

ASD...

[This message has been edited by Al Dyer (edited 06 August 2001).]

 

[AllenLee]

Thank you all for your great effort!


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Allen Lee