Modeling and Analysis of Re-entrant Production Systems

Abstract

This paper presents a model and analysis of a re-entrant production line with finite buffers and unreliable machines. Semiconductor device and liquid crystal display (LCD) fabrication processes are characterized as a re-entrant process, in which a similar sequence of processing step is repeated several times. This re-entrant behavior of material flow with the stochastic nature of the system caused by machine failures or demand changes makes the system difficult predict and analyze.

The decomposition method analyzes the behavior of the manufacturing systems by decomposing a long transfer line into small analytically tractable components, called two-machine line building blocks. Existing decomposition methods are limited to an in-linear production system without re-entrant flow. Since many manufacturing systems, particularly semiconductor and LCD production lines, consist of re-entrant flow paths, it is essential that models be developed to reflect this.

The purpose of this paper is to present mathematical formulations and algorithms to analyze the material behavior of the re-entrant production system using the decomposition method. In developing equations for the two-machine building blocks for the re-entrant production line, we modify the existing decomposition model that has been created for the multiple-part type line. Two main performance measures are evaluated with the developed mathematical model: production rate and average inventory levels for each buffer space in the system. The qualitative behavior of the re-entrant production line under different machine parameters and demand scenarios is also described.