Many assembly lines of complex products are divided into segments (zones and sections), each with its own manager. While zones are usually large and derived from the nature of the process, the segmentations to smaller sections is less obvious.
The purpose of this paper is to obtain and to expose considerations related to division of assembly lines into segments, and to develop a framework to assess the impact of line segmentation. In particular the paper investigates the decision related to number of stations in each segment and its impact on costs, throughput, and span of control.
Three major factors related and identified: (1) Stoppages: any disruption that temporarily stops the regular assembly at a station (machine maintenance, product defects, worker related breaks, external events etc. (2) Absenteeism and turnover: requiring a slowdown due to a learning period of the substitute workers. (3) Span of control: supervisory assistance is spread across the stations of each section. Therefore it is a major motive for segmenting the line. The paper analyses and discusses the contributions of sections to the operation of large assembly lines, and their associated impediments. Quantitative models are developed to represent the effect of each of the main factors, and bounds are found for the sections length. An important implication of dividing the hundreds of stations into small sections is that each section can be efficiently designed and balanced independently, rendering the optimization complexity irrelevant for these bounded sections. In addition, finding effective upper bounds to number of stations in a line section establishes the practicality of exact methods for designing and balancing each section.
The model provides a framework of considerations that enables the designers of assembly lines and production lines to determine the appropriate division of the line into sections and zones, and the best allocation of stations to sections.
