Optimally loading clocked tow trains for JIT-supply of mixed-model assembly lines

In today's mixed-model assembly production, there are two recent trends in particular, namely increasing vertical integration and the proliferation of product variety, which more and more shift focus to an efficient just-in-time part supply. In this context, many automobile manufacturers set up decentralized logistics areas referred to as "supermarkets". Here, small tow trains are loaded with parts and travel across the shop floor on specific routes to make frequent small-lot deliveries which are needed by the stations of the line. This paper investigates the loading problem of clocked tow trains, which aims at minimizing inventory near the line while avoiding material shortages given the limited capacity of tow trains. An exact solution procedure with polynomial runtime is presented and interdependencies with production planning, i.e., the sequencing problem of product models launched down the line, are investigated.