Assembly line segmentation: Determining the number of stations per section

Purpose - The purpose of this paper is to ascertain and expose considerations related to the division of assembly lines into segments, and to develop a framework for assessing the impact of line segmentation. In particular, the paper aims to investigate the decision regarding the number of stations in each segment, and its impact on costs, throughput, and span of control. Design/methodology/approach - The paper analyzes the literature, identifies the main considerations related to assembly line segmentation, and develops a mathematical model that reflects important factors related to the impact of segment length on the throughput and costs. The paper derives several important bounds on the number of stations (length) of a line's segment, which should be incorporated in the final design of the line sections. Findings - A trade-off was found between the revenue (and throughput) and the buffer spaces located between each pair of sections of an assembly line. The higher the product price, the shorter the segments are. On the other hand, when buffer costs are higher, the line segments are longer (fewer sections and buffers are used). Interestingly, except of stoppages, the other two dominant factors in the segmentation decision are: absenteeism, and span of control. Using these factors, various upper bounds were found on the number of stations per section (which determine the total number of sections). The tightest upper bound is the active one, and this ensures line sections with a small number of stations. Practical implications - The model provides a framework of considerations to help designers of assembly lines and production lines determine the appropriate division of the line into sections and zones, and the best allocation of stations to sections. In addition, finding effective upper bounds for the number of stations in a line section establishes the practicality of exact methods for designing and balancing each section. Originality/value - This is the first paper to offer a quantitative treatment of the various factors affecting assembly line segmentation. By finding the upper bound on the number of station per section, the paper establishes the practicality of exact methods for designing and balancing each section separately. Moreover, it provides a sound basis for future research related to design of assembly and production lines, and management of sequential processes.