Fleet sizing and cyclic delivery scheduling for in-plant inventory routing problem

We study the in-plant material supply system from a decentralized in-plant warehouse to workstations of a assembly line. The deliveries are done with vehicles called tow trains and wagons attached to them. Determining the number of trains to serve, number of wagons attached to each train, amount of materials carried, and delivery schedules are some of the decisions made. Especially on narrow aisles, vehicle congestion effects making these decisions. The in-plant inventory routing problem considers finding delivery routes and schedules of trains with minimum cost. Out objective is to determine the minimum cost fleet size, cyclic delivery routes and schedules that do not allow stock outs at workstations while considering congestion. In this study, a mixed integer linear programming model is introduced. Due to the complexity of the problem, we introduce a heuristic to find good quality solutions. The effectiveness of the algorithm is tested on randomly generated test instances.