Bi-directional work sharing in assembly lines with strict and flexible assembly sequences

Work sharing between stations in assembly lines can reduce cycle time and improve throughput rate. This research addresses assembly lines in which tasks may be shared with their immediate upstream or downstream stations only. This study consists of three stages. In the first stage, we assume that all work content in the line can be shared. Then, the balanceability of the line, which is defined as its ability to achieve a perfect balance (identical workload in all workstations) via work sharing, is examined. An algorithm and a linear programming formulation is proposed to provide the sharing proportion, namely, the percentage of the cycles each station performs the shared task. In the second stage, a line with partial sharing is investigated; conditions for balanceability are provided as well as a solution approach for obtaining the sharing proportions of the shared tasks. The last stage considers the most practical model in which sharing costs are involved, and the identity of the shared tasks is to be determined. Mixed-integer linear-programming models and a custom-made search algorithm are developed to minimise the cycle time given a limited sharing budget, for strict and flexible assembly sequences. Experimentation to evaluate the performance of the formulations and the effect of the problem parameters on the run time is conducted.