Mixed-model assembly lines under cyclic production: Models for productivity improvement and teamwork

In this dissertation we develop a modeling framework of mixed-model unpaced assembly lines where high content of manual labor is involved. The modeling framework is then used to address questions of labor organization in such assembly lines through use of teams. The motivation for the team models considered in this dissertation comes from the practices observed in automotive industry. Despite extensive use of workteams in assembly lines by some automobile manufacturers, very little has been known about the effects teams have on productivity. This thesis offers a formal modeling framework to provide means of evaluating the implications of various team structures on productivity of the assembly line. The modeling framework of mixed-model assembly line is shown to be quite flexible to incorporate a number of scheduling and operational control issues related to flexible assembly lines. The approach bridges scheduling and operations strategies with human resources strategies in mixed-model assembly lines. Such a bridge is achieved through effective use of lot sizing and inventory control strategies, through cyclic production schedules and worker paced production involving work sharing in teams. Several types of teams, depending on the production environment, are considered. In particular, two polar types of team structures, The Japanese Model, which originated as part of the Toyota Production System, and The Scandinavian Model, which originated in Sweden are incorporated in the modeling framework. We find that teamwork does not always lead to productivity enhancement. We characterize situations under which teamwork by cross-trained workers improves and worsens productivity. We provide guidelines on how to form teams of workers and how to organize teamwork within the boundaries of the team in order to improve productivity of the assembly line. This dissertation also investigates how expansion and reduction of the workforce in a mixed-model line affect productivity. The proposed teamwork models are tested using assembly line data from a major automobile company