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It is the requirement that a quality characteristic should meet. It could apply either with a single specification limit or two specification limits. Unknown Variabi ariability lity ± Range Metho Method.
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Unkn Un know own n Var aria iabi bili lity ty ± St Stan anda darrd Dev Devia iati tion on Me Meth thod od. Gen ener eral al de desc scri ript ptio ion n of of sam sampl plin ing g pl plan an, sa samp mple le K = Acceptability Constant M = Maximum Allowable Percent Nonconformity Variability Unknown (Standard Deviation Method) normally Composition of the standard: 9 different procedures to evaluate a lot. MIL-STD-414 ASQ closely match ANSI/ASQ Z1.4 and ISO/DIS 3951. Shainin states that the plot is close distribution c lose enough to have no practical effect on the final decision, or if there are any errors, they are in a safe direction. The major criticism major criticism of the plan is that the shape of the plot does not always always give an accurate indication of the true distribution. Many users of the lot plot method have modif ied ied the Shainin method for their own situation. Inspectors can accept lots however, disposition of unsatisfactory lots is left to a material-revi material-review ew board board. Unacceptable lots are returned to the producer, and this action will cause a subsequent improvement improvement in quality. Learned, the lot plot procedure is relatively simple and has resulted in improved quality and lower inspection cost. Review board determines the final disposition of the stock. percentage of product beyond spec is obtained. Ranges:: Ranges Factor for Central Line d2ĭecision is based on a comparison of the lot plot with different types of lot plots. The average, X-bar and range, R, are calculated for each subgroup.Ī histogram is constructed (number of cell: 7-16).Ĭalculate the average of averages, X-double bar, and average of ranges, R-bar.Ĭalculate the upper and lower lot limits (ULL The method for obtaining the lot plots is as follows: Ī random sample of 10 subgroups (g) of 5 each for a total of 50 items is obtained from the lot. inspectionĪpplicable to both normal and non-normal frequency distributions. It is a practical plan for in-house for in-house inspection inspection. The plan uses a plotted f requency requency distribution (histogram) to evaluate a sample for decisions (accept/reject a lot). Process Parameter To control the average av erage and standard deviation of the distribution of the product to specified level E.g.: Acceptance control chart Sequential sampling for variable Hypothesis testingĭeveloped by Dorian Shainin (Hamilton Standard Division of United Aircraft Corporation, 1950). Percent nonconform nonconforming ing To determine the proportion of product that is outside specification s pecificationĮ.g.: Shainin lot plot ANSI/ASQ Z1.9-1993 Types of Variable Sampling Plan Variable Sampling Plan Possibility of no nonconformity in a rejected lot.ĭependence on assumption of distribution shape. Higher High er clerical clerical cost cost ± Calcu Calculati lation. Higher High er inspection inspection cost ± Meas Measurem urement. Same protection with smaller sample size.Įrrors in measurement more likely detected.ĭisadvantages of Variable Sampling Plan: Īpplicable to only one quality characteristic at a time. Percent nonconforming below and above specifications. normal distribution) it is possible to use a sampling based on sample measurements such as: Mean Z1.9 9 Ī quality characteristic is measurable on a continuous scale, scale, and is know to have a distribution of a specific type (e.g. Shai Shainin nin Lot Lot Plot Plan Plan. Process Fraction Nonconforming Type of variable sampling.Īn Introduction. The advantages and disadvantages of variable sampling. At the end of this topic, students will be able to: Discuss