Analysis of Takt Time Extension in Assembly Lines with Multiple Elemental Works Allocated to a Process

In recent years, in response to the diversification of customer needs and the shortening of product life cycles, there has been a shift towards establishing multiple production lines for each product, similar to cell production. Such production lines generally consist of multi-elemental work process, which multiple elemental works are allocated to a process. However, in production lines constructed with such multi-elemental work processes, it is often observed that operations cannot be carried out at the targeted tact time, resulting in a failure to meet production goals. In the production line under investigation in this study, the discrepancy between planned tact time and actual execution tact time also has been a problem. Therefore, in this study, we conducted an analysis of the factors causing an extension of process work time in multi-elemental work processes through the analysis of a manual assembly line for white goods appliances and assembly work experiments. The study clarified that, when estimating multi-elemental work process work time, it is necessary to consider not only the execution time of component elemental work but also the time for interruptions in operation and cognitive processes.