Multi-objective assembly line balancing considering component picking and ergonomic risk

Aim of the assembly line balancing problem (ALBP) is the efficient and effective assignment of assembly tasks to stations in one-piece-flow production systems. Although this problem has been studied for decades, few contributions consider the component picking at assembly station level. Yet, this activity has relevant and practical implications for ALBPs in the industrial context. This paper proposes an innovative multi-objective optimization model for the ALBP to assign the assembly tasks to stations by distinguishing the assembly activities involved in task execution and component picking. Thus, a function is proposed to relate the time required for component picking with the component storage location at assembly station level and the component features, namely dimensions, weight and handiness. The aim of the developed model for the ALBP is the simultaneous minimization of the assembly line takt time and ergonomic risk, both determined by the task execution and component picking activities. Furthermore, the proposed model not only defines the optimal task assignment to stations, but it also determines the optimal storage location of each component between the locations available at the different assembly stations. The multi-objective optimization model is validated with an industrial case study dealing with a kitchen appliance assembly line. The final assembly line balancing configuration proposed is distinguished by remarkable performance for both takt time and ergonomic risk objective functions. Such a balancing leads to 36% ergonomic risk reduction with just 2% takt time increase compared to the correspondent single-objective configurations. These outstanding results are determined by a proper component disposition in the different station storage locations defined by the model.