Reducing gaging frequency/High Cpk

[Dura_guy]

I have a few processes that are extremely capable (> 7.0 Cpk). In QS-9000 4.9.2, reference is made to revising the control plan when a high degree of capability is demonstrated. Is there any guidelines as to how this can be accomplished, (other that atmospheric analysis?)

Currently we are gaging for these characteristics at a frequency of 3 pcs. per hour of production. Is there a formula I can apply that can help me determine if I can reduce the frequency of checks to every 2,3,4....etc. hours?

Thanks for your help!

Dura guy

[noboxwine]

7.0 Cpk ! Wow ! I am sure that there is some esoteric, mathematical formula that can be used as a guideline for adjusting your frequency. But, here's what I have done in similar situations. First, is your process in CONTROL? I can show you a high Cpk all day long, but if the process is not in statistical control, then you can't predict it. If it is, I would simply use common sense (sorry, I tend to throw that in and confuse a lot of people) and change your freqeuncy to, say, every 1.5 hrs and monitor accordingly. If it's still good, 2 hrs. Simply let the data tell you how your process is behaving and reduce needless inspection accordingly. I am sure you'll find it pretty simple and effective. Rot's of ruck and have a nice day.

[Mike S.]

I agree with Noboxwine, but if you want a non-esoteric mathematical formula, one "guideline" I've used is 6 measurements between adjustments to the process. This won't work everywhere, but try noboxwine's idea and see if it would jive at all with mine.

Let us know how it works out. Maybe we'll all learn somethin'

[D.Scott]

I am certainly in agreement with the comments so far but remember that a change in the control plan should be run past the customer. Also, if you just open up your intervals, you stand the chance of going past the optimum before you realize it.

Why not take the control chart you currently have and do run studies based on that data. Calculate using every other entry for 2 hours, every 3rd for 3 hour etc. This will show what the capability will look like at those intervals. Include the studies with an analysis of the data and present the facts to the customer telling him you intend to change the intervals on the control plan.

When he agrees, make your change. This way, the data is still there and current in case you run into a problem. It is also less confusing to the employees who are collecting the data.

Dave

[Mike S.]

Sage advice. Wish I'da said it first.

And Energy said common sense was dead! Not completely it ain't!