Network flow procedures for the analysis of cellular manufacturing systems.

1. Introduction

In a traditional manufacturing process layout, machines are assembled together to devise independent machining centers with functionally identical machines in each group. In this type of layout design, a batch of parts requiring a

known sequence of operations is routed through the associated machine centers according to the specified sequence. A cellular layout, in contrast, is an arrangement of different machines into manufacturing cells on the basis of similar processing requirements to produce one or more families of parts. Machines within a cell work only on those parts that belong to the family or families assigned to the cell. Through the simplification of operational routings, cellular manufacturing systems have been identified as systems that can produce a family of similar parts more economically owing to the significant reduction in material handling and setup costs (Burbidge, 1975).

According to recent surveys (Kusiak, 1990), a 20-60% reduction in production lead time can be related to reduction in setup time. These surveys also indicate that a 15% space saving, and a 20-88% reduction in material handling efforts can be achieved by implementing manufacturing cells. Moreover, because cellular manufacturing focuses on the simplification of material flow, it makes it easier to schedule parts and track the status of shop orders. However, a comprehensive approach covering all important variations of the cell formation process has not yet been achieved. The proposed methodology represents a significant step in this direction.

Network-flow models and solution techniques can be of great value in the design, improvement, and rationalization of complex large-scale systems. The advantages of using network models include the accurate representation of real-world systems, as well as the relatively high computational efficiency of network algorithms. This article develops a network-flow-based procedure for grouping the machines of a manufacturing system into cells, and the parts to be processed into families, in such a way that the overall intercellular flow of parts is minimized. To develop a meaningful comprehensive cell formation approach, the following two important cases are considered:

Case 1: restricted number of cells and unrestricted cell size;

Case 2: restricted number of cells and restricted cell size.