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Invigilation plans for monitoring the quality and reliability of continuously produced product

Prairie, R.R.; Zimmer, W.J.

Part of the evaluation process that occurs during production of many complex components is performance testing of fabricated units as they are being produced. The results of these tests are used monitor the quality and reliability of the product and to contribute to the data base for reliability assessment. This paper presents an approach for designing plans for the evaluation of continuously produced product where the testing may be either destructive or non-destructive. The philosophy of the plans is to initially test a string of consecutive units at the beginning of production to show that the design and manufacturing processes conform with the required reliability. Once the product has passed the initial testing, a sampling phase is begun. If the product continues pass, a reduced sampling rate phase is used. Failures in the initial phase or the first sampling phase cause the plans to revert to the initial phase restart. If a failure occurs during the reduced sampling, the estimated failure rate is checked for concordance with the reliability requirement. This check is made to allow for continuation of sampling if the cumulative number of failures is consistent with the reliability requirement. A selection of values for the parameters of the plans and a rule for determining concordance are presented. The parameters of the plans are related to the AQL and LTPD concepts of acceptance sampling and the average number of defective units passed before a defective unit is sampled and detected.