Efficiency of paced and unpaced assembly lines under consideration of worker variability – A simulation study

Incorporating recent findings from behavioral operations, we compare paced and unpaced assembly lines with respect to their steady-state efficiency via simulation. In particular, workers can speed-up their service times when needed to feed downstream workers or to unblock upstream workers. The study finds that unpaced lines are superior to paced lines for many real-world settings, i.e. in mixed-model production environments with a long line length. However, the benefit they provide has been overestimated in previous studies because of simplifying assumptions such as the disregarding of state-dependent behavior or worker fatigue. With an inhomogeneous workforce, the efficiency is also sensitive to worker placement. In unpaced conditions, an inexperienced worker should be placed in the middle of the line, while in paced conditions, he should be placed to the first workstation. Workers capable of speed-up should be placed in the middle of the line in both line types.