Production and vehicle scheduling for ready-mix operations

This paper deals with the problem of selecting and scheduling the orders to be processed by a ready-mix manufacturing plant for immediate delivery to the customer site. Orders have a fixed due date and must be prepared in a single plant with limited capacity. The objective is to maximize the total value of orders served. We first describe the problem as it occurs in practice in some industrial environments, and then present two scenarios to be considered: arbitrary and uniform profits margins for orders. The first scenario corresponds to the fixed job scheduling problem, which is solved by a minimum cost flow problem. A new scheme that reduces the number of nodes in the graph is proposed in this paper. The second scenario on the other hand requires more computationally expensive approaches as a second objective of minimizing the number of vehicles is to be considered. An exact graph-based method and a heuristic branch-and-bound scheme are described. Computational experiences show that the optimal approach is not feasible for large problems and that the proposed heuristic approach gives high-quality solutions in short running times.