Integrated real-time control of mixed-model assembly lines and their part feeding processes

摘要

Mixed-model assembly lines enable a flow-oriented mass production of individualized products such as cars. The most investigated operational decision problems in this domain are the sequencing problem, which plans the initial sequence of cars launched down the line, and the resequencing problem, which alters a given car sequence by applying resequencing buffers. This dichotomy of existing research neglects a third, even more short-term decision level: launch control under real-time conditions. In large automotive assembly lines unforeseen disturbances are rather the norm, so that one of the most important decisions to maintain a smooth and error-free production flow is the continuous launching decision of the next car model released from the central chassis storage system into final assembly. The launching decision in every cycle is made in a central control room (or leitstand) and has to consider the current state of the assembly line itself, with all potential time delays and defects in any assembly station, along with all part feeding processes under realtime conditions. This paper provides an integrated solution approach for real-time launch control that applies sophisticated optimization procedures considering both the workflow along the assembly line and its impact on part feeding processes. We test our real-time approach in a simulation study and compare it with alternative launching approaches. Our results show that sophisticated real-time optimization clearly outperforms its competitors. Furthermore, an integrated approach including part feeding aspects can considerably reduce safety stocks of parts within workstations.