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  Statistical Techniques and 6 Sigma
  Continous Flow Sampling Plans

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Author Topic:   Continous Flow Sampling Plans
MCDeNovo
Lurker (<10 Posts)

Posts: 2
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Registered: Apr 2001

posted 02 May 2001 04:30 PM     Click Here to See the Profile for MCDeNovo     Edit/Delete Message   Reply w/Quote
I currently use a C=0 sampling plan with a default AQL of 4.0 for visual inspections on the production floor. Production is moving from batch processing to continous flow. Where can I find information for developing a sampling plan to use in a continous flow process as opposed to a batch process?

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Johnny Jewel
Lurker (<10 Posts)

Posts: 2
From:Mid-MO
Registered: Apr 2001

posted 03 May 2001 10:34 PM     Click Here to See the Profile for Johnny Jewel     Edit/Delete Message   Reply w/Quote
There is an ASQ publication, ćHow to Perform Continuous Sampling (CSP)ä by Kenneth Stephens. Some of the sampling schemes it considers are from the old MIL-STD-1235C, which, for some reason, was not carried over to be an ANSI/AQC specification as, for instance, MIL-STD-105E was. Juranās 3rd Edition is good also; from the 4th on, too much condensation was done to be of much value.

My organization studied continuous sampling during the development of a new product line. Our historical assembly method was by 1 person start-to-finish. The new product was concurrently designed with a new assembly line production process, and testing was changed from batch method (105E) to a continuous sampling plan. CSP-V met our requirements and has been in use for about 4 years.

The scary part of CSPās is the requirement of 100% inspection at the beginning and whenever a non-conformance is detected. This can make the concept a hard sell, and growing into the plan can be agonizing. Batching for this product/assembly line would have been completely artificial, considering the nature of part flow to the line and the way the product is adjusted during/after assembly. One feature that is designed into the plans is that there is no retrieval when a non-conformance is detected. Depending on the plan chosen, you either immediately re-sample for verification or go immediately to 100% inspection until some clearance number of continuous OK product is reached. Then you go back to sampling. There are trade-offs among the types of plans, the main one being that as the % sampled decreases, the clearance number gets larger and vice-versa.

The good news for us was that the product was robust for the characteristic tested. At least that is how some have viewed the experience. There also was a big incentive to develop the product ö tune it, continuously improve it -- to keep it out of the dreaded 100% inspection. In other words, we may have more confidence in this product because of the sampling plan that was chosen.

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dWizard
Forum Contributor

Posts: 20
From:Normandy, TN 37360
Registered: Mar 2001

posted 04 May 2001 09:22 AM     Click Here to See the Profile for dWizard   Click Here to Email dWizard     Edit/Delete Message   Reply w/Quote
This site http://www.variation.com/library.html has some good stuff on sampling.

This site http://www.variation.com/techlib/standard.html has some standards for download that may be of use.

Regards,
dWizard

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I was better but I got over it.

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