Optimal sequencing of mixed models with sequence-dependent setups and utility workers on an assembly line

This paper presents an integer programming formulation for the sequencing problem in mixed-model assembly lines where the number of temporarily hired utility workers and the number of sequence-dependent setups are to be optimized simultaneously through a cost function. The resultant model offers an operational way to implement the utility work needed to avoid line stoppages, unlike previous papers addressing the goal of smoothing the workload. The present research has an immediate application to the automotive industry, namely to the car-sequencing problem. Simulation results show that the proposed formulation leads to the optimum in a reasonable time for instances up to 15 items and to satisfactory feasible solutions for some of the larger problems we considered within a moderate time limit.