INPUT CONTROL FOR SERIAL PRODUCTION LINES CONSISTING OF PROCESSING AND ASSEMBLY OPERATIONS WITH RANDOM YIELDS

This paper deals with a serial production line where each of the stage s can be either a processing or an assembly stage. A processing stage processes outputs from an upstream stage and transforms them into inpu ts for the downstream stage. Each processing stage is subject to yield losses. At an assembly stage, a batch of identical input components i s processed and the nondefective components art then combined with the output from the upstream stage. The processing operation for the inpu t component is imperfect. For such a system, we characterize the form of the optimal policy for input quantity at each stage in the producti on line, when stochastically proportional yield is assumed at each sta ge, i.e., the distribution of the yield fraction is assumed to be inde pendent of the lot size. The optimal policy exhibits same form of a cr itical number policy. For production lines consisting of assembly stag es only, the critical numbers can be computed easily. When yields are of the ''exponential'' type, the critical number policy is still optim al, although there are interesting differences in the policies for the different types of yield characterizations.