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Use Sequential Sampling To Reduce Inspection Costs
Basics of ANSI/ASQ Z1.4 sampling plans, including the switching rules
Benefits of double and multiple sampling plans in terms of lower average sample numbers (ASNs)
Convert any ANSI/ASQ Z1.4 plan into a sequential sampling plan in a simple tabular form that is easy to use on the shop floor.
Generate the operating characteristic (OC) curve for the sequential plan to show that its protection against poor quality is almost identical to that of the original plan (exactly identical at the two points that were used to develop it). Also plot the ASN against the1. nonconforming fraction to quantify the likely savings on inspection.
For awareness only; there are alternatives to the traditional ANSI/ASQ Z1.4 plan and sequential sampling.
Zero acceptance number sampling, a form of discovery sampling, requires very little inspection but also requires quality far superior to the specified acceptable quality level to avoid rejection of lots that meet the requirements.
Narrow limit gauging can reduce the required inspection enormously. It requires that the quality characteristic be normally distributed, and that increases in the nonconforming fraction result solely from a change in the process mean.
Overview of the webinar
ANSI/ASQ Z1.4 sampling plans can be converted into sequential sampling plans by selecting two points on their operating characteristic (OC) curves. The OC curve shows the probability of acceptance versus the nonconforming fraction (p) in the lot. The two points are generally (1) the acceptable quality level (AQL) or,more precisely, the nonconforming fraction at which the chance of rejection is 5 percent and (2) the rejectable quality level (RQL) at which the chance of acceptance is only 10 percent. (While ANSI/ASQ Z1.4 plans do not have formal RQLs, we treat the nonconforming fraction for which the consumer's risk of acceptance is 10% as the RQL.) This results in a sequential sampling plan that can be tabulated in the form, as an example,
If 0 nonconformances, accept on the 40th item inspected.
If 1 nonconformance, accept on the 73rd item
If 2 nonconformances, reject on 16 or fewer items inspected, accept on the 107th.
If 3 nonconformances, reject on 49 or fewer items inspected, accept on the 140th.
and so on.
As truncation rules require a decision at some specified point, the entire plan may require fewer than 10 rows. The user can also show the operating characteristic (OC) curve for the sequential plan with that of the original ANSI/ASQ Z1.4 plan to assure the customer that it does in fact provide comparable protection against poor quality.
Who should attend?
Quality managers, engineers, and technicians, and others with responsibility for acceptance sampling activities
Why should you attend?
Inspection is a mandatory but non-value-adding activity so, the less we have to do, the better. ANSI/ASQ Z1.4 (formerly MIL-STD 105) sampling plans for attribute (pass/fail) data seek to reduce the amount of inspection with double and multiple sampling plans. Sequential sampling, in which the successive sample size is one item, is even more efficient and plans can be developed on a spreadsheet. Attendees will receive a copy of the spreadsheet that was used to develop the examples in the presentation, and the inputs can be modified to reflect the user's need.
This webinar also shows how to deploy the sequential sampling plan in a very convenient format for use on the shop floor, where acceptance or rejection depends on the number of items inspected versus the number of nonconformances found. (The traditional format is far less convenient because it can have more than a hundred rows, e.g. 1 to 100 or more, for items inspected and acceptance or rejection depends on the nonconformances found.)
Faculty - Mr.William A. Levinson
William A. Levinson, P.E., is the principal of Levinson Productivity Systems, P.C. He is an ASQ Fellow, Certified Quality Engineer, Quality Auditor, Quality Manager, Reliability Engineer and Six Sigma Black Belt. He is also the author of several books on quality, productivity and management, of which the most recent is The Expanded and Annotated My Life and Work: Henry Ford's Universal Code for World-Class Success.