Consider an N stage serial production line where the processing times of orders may be random. Since the carrying costs increase from stage to stage, the standard production procedure, that is, to determine a total leadtime for the entire order by taking an appropriate percentile of the distribution of total processing time and then release the order immediately from stage to stage during the process, may not be optimal since it ignores inventory carrying costs. This article studies a per stage planned leadtime dispatching policy for such systems. The order will not be released immediately to the next workstation prior to a predetermined delivery time, or planned leadtime. The vector of planned leadtimes at workstations is to be determined by trading off expected holding costs at all stages and expected penalty costs for exceeding the total planned leadtime. We show that the optimal vector of planned leadtimes may be obtained efficiently by solving an equivalent serial inventory model of the type considered in Clark and Scarf (1960).serial production system, random processing time, leadtime planning
This paper considers the problem of test design and implementation when testing is imperfect. Items that are classified as conforming may be nonconforming, resulting in a poor outgoing quality level. Items that are classified as nonconforming may be conforming, resulting in excessive scrapping of conforming items. The failed items are commonly retested to reduce the scrapping problem. Alternatively, the accepted items may be retested to improve outgoing quality. In this paper, we examine the question of whether it is better to repetitively test rejected items, or to repetitively test accepted items. We also examine the relationship between the two testing policies, testing equipment accuracy and capacity, incoming quality, and outgoing quality requirements.Computer/Electronic Industry, Semiconductor Manufacturing, Inspection, Optimal Testing Strategies
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