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  Statistical Techniques and 6 Sigma
  Reactions to out of control X bar and R charts?

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Author Topic:   Reactions to out of control X bar and R charts?
Josh Smith
posted 01 October 2000 12:26 PM           Edit/Delete Message   Reply w/Quote
I am curious as to how other organizations have written their procedures for reacting to out of control points up or below the control limits, 7 consecutive points running above or below the centerline, and 7 points trending up or down?

Our reaction plan on the control plan states that when the process has violated these rules. Supervisor will be notified by quality auditor, suspect product will be isolated and verified by other means (i.e 100% inspect), the process will be adjusted to bring back into a state of control, and process changes will be noted on the process change log sheet.

Does this sound reasonable? Or is it painting us into a corner for QS-9000?

Looking for input?

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Lurker (<10 Posts)

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Registered: Sep 2000

posted 04 October 2000 03:03 PM     Click Here to See the Profile for auditor16949   Click Here to Email auditor16949     Edit/Delete Message   Reply w/Quote
The procedure is basically OK. The QS-9000 auditor may ask if you have identified and eliminated the special cause of variation acting on the process.

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Lurker (<10 Posts)

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From:Beech Grove, IN, USA
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posted 17 October 2000 11:08 AM     Click Here to See the Profile for Indywine     Edit/Delete Message   Reply w/Quote
Keep in mind that 7 points in a row usually reflects a change in the process. However, it could be associated with a learning curve after training. I wouldn't suggest blindly changing the process without trying to understand why there is a new trend.


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From:Salem, Oregon
Registered: May 2000

posted 17 October 2000 01:45 PM     Click Here to See the Profile for lyman   Click Here to Email lyman     Edit/Delete Message   Reply w/Quote
Our procedures which were written by engineering and approved through manufacturing centered the responsibility for initial monitoring of SPC and any related trends with the floor operators. We tied our SPC as much as possible with our computerized manufacturing system so that if the chart showed an OOC point the equipment automatically was no longer available to production until such time that someone from Engineering reviewed the situation and released it. The procedures for trends directed operators to OCAPs which either dictated that a change to equipment settings be made (if appropriate)with the requisite documentation, or that the process be shut down and Engineering and Manufacturing Management be notified. The biggest challenge we faced with this allocation of responsibility was making sure that there was enough information in our computerized record so that Engineering could evaluate the situation to begin effective corrective or preventive action. The second biggest challenge - getting Engineering to document what they did!

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Brian Dowsett
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From:Waterford, Ireland
Registered: Nov 1999

posted 24 October 2000 12:12 PM     Click Here to See the Profile for Brian Dowsett   Click Here to Email Brian Dowsett     Edit/Delete Message   Reply w/Quote
I think you also could make some reference to process capability.
For instance if you have a very good Cpk value, seven points in one direction definitely merits some attention but may not merit 100% inspection.
In a previous job, our reaction plan was in the form of a flow chart, with some decision boxes based on proven process capability.



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