Design of multi-product manufacturing lines with the consideration of product change dependent inter-task times, reduced changeover and machine flexibility

Traditional research work in manufacturing line design assumes that the times between manufacturing tasks performed on a workstation are independent of the task sequence on that station. Furthermore, such studies paid little attention to the sequence dependent inter-task times in multi-model production. Since the inter-task times related to product model changeover have significant impact on manufacturing line performance, it is necessary to take into account the inter-task times explicitly in multi-model manufacturing line design. The need for this consideration is growing as product variety increases. This paper presents mathematical models of manufacturing line design with the consideration of product change related inter-task times in evaluating station times for multi-model production. An optimization model is developed using mixed integer programming to minimize manufacturing line cost. The model takes into account the recurrence of manufacturing tasks in a station to determine the machine type in a station. This paper also presents a heuristic solution procedure developed for efficient calculation. This paper also investigates how product model build sequences and inter-task times affect manufacturing line performance. The developed models will help enhance task-station assignment in multi- and mixed-model production by increasing line cost effectiveness and reducing line changeover impact as well as shortening long re-balancing processes.