Push-pull production planning of the re-entrant process

Thin film transistor and liquid crystal display (TFT-LCD) fabrication manufacturing is characterised as a re-entrant process, in which a similar sequence of steps is repeated several times. Production control for the re-entrant process is complex, since, without intelligent control, it may incur the congestion of WIP or equipment idleness because of the work in progress (WIP) shortage. In this paper, three kinds of control policies are suggested: push, push-pull and pull types. Exact formulations using linear programming are given, and their performances of solutions are evaluated. It is shown that a pull type control policy gives stable throughput and delivery satisfaction at a small cost and with less production. A push type policy outperforms the other two types in the throughput and manufacturing cycle time.