Process Analysis Sampling Plans - General Purpose
A common challenge that quality control engineers face is to determine how many items from a batch (e.g., shipment from a supplier) to inspect in order to ensure that the items (products) in that batch are of acceptable quality. For example, suppose you have a supplier of piston rings for small automotive engines that your company produces, and your goal is to establish a sampling procedure (of piston rings from the delivered batches) that ensures a specified quality. In principle, this problem is similar to that of on-line quality control discussed in Quality Control. You may want to read the Introductory Overview at this point to familiarize yourself with the issues involved in industrial statistical quality control.
- Acceptance sampling
- The procedures described here are useful whenever you need to decide whether a batch or lot of items complies with specifications without having to inspect 100% of the items in the batch. Because of the nature of the problem - whether to accept a batch - these methods are also sometimes discussed under the heading of acceptance sampling.
- Advantages over 100% inspection
- An obvious advantage of acceptance sampling over 100% inspection of the batch or lot is that reviewing only a sample requires less time, effort, and money. In some cases, inspection of an item is destructive (e.g., stress testing of steel), and testing 100% would destroy the entire batch. Finally, from a managerial standpoint, rejecting an entire batch or shipment (based on acceptance sampling) from a supplier, rather than just a certain percent of defective items (based on 100% inspection) often provides a stronger incentive to the supplier to adhere to quality standards.
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