Reducing the Frequency of a Production Line Test

S

Sturmkind

#11
I agree with Bev that a runchart to specification limits is absolutely needed to check for potential out-of-control conditions including runs larger than 6 in a row, stratified groups (hi to low to high), and so forth.

Is there a reason for a 10 pc. sample? Nine would afford 3 sub-groups of 3.

Once you prove a state of control, the sampling frequency may be intuited from the display. I think your earlier list of NCR's, Cpk & Cp (or CR) estimate, etc. is good.
 
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bobdoering

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#12
...what is the severity of the failure resulting from a defective part? A very severe failure might require continued high frequency because we can't afford a miss should it happen. Remember that statistical control today doesn't guarantee control tomorrow....
I agree 100%. A very severe failure or a very expensive sort can be convincing arguments to continue high frequency checks. Sometimes you can never reduce the test frequency, just for those reasons!


A run chart (all individual values if you use subgroups of n>1) vs spec limits is a better display of all of the data as shifts, trends and cycles are visible.
Charting may provide adequate ongoing evidence that the process has sufficient monitoring frequency. It may be your only hope...so consider it.

I think your earlier list of NCR's, Cpk & Cp (or CR) estimate, etc. is good.
I would not put much credence in capability values. They have little descriptive or predictive value.
 
Q

Qualityfan34

#13
Thank you guys for your advices.

On the other hand, how can i calculate the Cost of Quality for this specific test?

Regards
 

bobdoering

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#14
On the other hand, how can i calculate the Cost of Quality for this specific test?
Well, Cost of Quality is really a gray area. Let me show you:

Some may claim that any costs associated with this test is a negative cost of quality, because the quality should already be in the part, and this is all overhead to sort.

Others may look at it and say that the costs involved with running the test are costs, but you can add the benefit of reducing any overhead from returns, customer dissatisfaction, addition of further labor or costs (except possible rework). At least with this approach one can see the value of protection - especially if foolproof prevention is not possible.

It just depends on the accounting principles you use in your cost of quality reporting system. The ultimate point is this: it is never actually correct, but it should be correct enough to give you decision making direction. It is like a gage. A gage is always bad….but it might be good enough. To be good enough, though, the techniques must be consistent throughout the analysis.
 
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Q

Qualityfan34

#15
Thanks Bob for your advice.

So let say that i reduce this test, how can i translate this reduction into the cost of quality? In other words, how can i calculate what was the before and after Appraisal Cost?
 
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