Moving From Every-Lot Inspection to Audit Sampling


Doganaksoy, Necip; Hahn, Gerald J.   (1994, ASQC)   GE Corporate Research and Development, Schenectady, NY

Journal of Quality Technology    Vol. 26    No. 4
QICID: 11389    October 1994    pp. 261-273
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Article Abstract

A major benefit of modern "up front" quality assurance is that, once process capability and stability are achieved, costly inspection of the final product from each lot can be replaced by audit sampling. In this case study the non-trivial practical and statistical considerations that arise in developing such an audit sampling scheme are described. Our application involves an extrusion process for an engineering plastic produced in lots. There are one-sided specifications on each of six physical properties. Traditionally, samples were taken from each lot. To replace this, an audit sampling procedure was developed. With audit sampling each kth lot is sampled unless the results show the need to return to every-lot inspection. In addition, the audit sampling results are monitored statistically to detect changes. The underlying criteria, the multivariate statistical plan, and various practical issues are discussed in this paper.


Case study,Monte Carlo methods,Multivariate analysis,Quality assurance (QA),Statistical process control (SPC)

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