CYCLIC SCHEDULING TO MINIMIZE INVENTORY IN A BATCH FLOW LINE

This paper addresses the problem of determining a cyclic schedule for batch production on a flow line. We assume a constant supply of raw ma terials and a constant demand for all finished goods. Material that ha s completed processing at one stage is transferred to the next stage i n small transfer batches. Inventory may be held before the line, at th e end of the line, or between any pair of adjacent stations. The objec tive is to find a sequence of production and a cycle length that minim ize the average cost per unit time of holding inventory. A linear prog ramming formulation is given that determines the optimal cycle length and finishing times for a given set of sequences, one for each machine . Two heuristics are presented for finding near-optimal sequences: one is applicable to the special case of a two-machine flow line;the othe rs are applicable to an m-machine line and focus on different aspects of the problem (e.g., cycle stock or work-in-process inventory). From a computational study, we have observed that: 1) permutation schedules , i.e., schedules with the same sequence on all machines, are nearly a lways optimal, 2) the heuristics produce near optimal solutions, 3) th e batching decision, i.e., the choice of cycle length, is substantiall y more significant than the sequencing decision for minimizing invento ry costs.