QUALITY CONTROL FOR EXPENSIVE ITEMS

Abstract : This analysis is concerned with the continuous control of a manufacturing process of expensive items which are produced singly and, in general, turned out without inspection. Their quality varies randomly, with a strong correlation, however, between adjacent items. An inferior item is assumed to inflict a certain loss, depending on the degree of inferiority. To keep the production process from deteriorating, periodically an item is sampled and inspected to check the manufacturing process. After each inspection, one of the following actions is taken: (1) continue production, and take another sample after a certain time, depending on the quality observed; (2) stop and revise the manufacturing process. The objective of the theory is to find a rule for the decision to be made after each inspection. This rule has to balance the advantage of revising the process against the costs of inspecting, and perhaps stopping it. (Author)