Workload Balancing and Scheduling a Mixed-model Assembly Line with Fractional Task Allocation

The present study discusses an extended problem of assembly line balancing with fractional task allocation. Fractional task allocation means that a task will be executed on one of paired consecutive stations. A fractional value gives the allocation ratio of the task on the upstream station against the downstream station. A mixed-model assembly line is assumed to accept the fractional allocation of a single task. Under the condition of mixed-model assembling, the duration of each task depends on the model. Therefore, buffer stations are necessary between stations to absorb the duration variation. However, preparing a buffer incurs a fixed cost, and thus it is a realistic assumption that the number of available buffers is limited. Therefore, examining the exact timing that a job arrives at each station and the buffer required is necessary to generate a feasible assembly schedule. The present study presents a mixed-integer programming model that includes three types of decisions; the allocation of tasks at each station, including a task with fractional allocation, the assignment of buffers, and the generation of a feasible assembly schedule. The objective is to minimize the cycle time under the given number of stations. Numerical experiments were conducted for problem instances with two and five models. Solutions support fractional allocation under the conditions of (i) there is a task that has a longer processing duration than the cycle time, and (ii) the model that involves such a task has a higher demand ratio. © 2023 Japan Industrial Management Association. All rights reserved.