Integrating competence-aware operator assignment into the mixed model sequencing problem

This paper investigates the impact of operator skills on the performance of mixed model manual assembly lines. The Mixed Model Sequencing Problem with Workload Minimization (MMSP-W) is extended to explicitly incorporate competence-aware operator-workstation assignments. This integrated problem (MMSP-W-OA) effectively reduces workload while minimising competence gaps across assembly line workstations. A modelling framework for quantifying operator performance based on their competencies is also provided and explained. Operators are assessed on multiple competency elements, and the resulting weighted sum of these elements determines the operator's task competency. This approach provides a holistic view of competency, taking into account task similarities and the full experience of operators. To cope with the increased complexity of MMSP-W-OA, a Benders-based fix-and-optimise heuristic is proposed. This method decomposes this integrated complex problem into manageable subproblems, reducing computational times to scales comparable to those of MMSP-W while maintaining reasonable solution quality. Experimental results reveal the mutual reinforcement between the sequencing and operator assignment processes, providing greater accuracy and higher work overload minimisation potential.