Divergent production scheduling with multi-process routes and common inventory

This research considers a scheduling problem in a divergent production system (DPS) where a single input item is converted into multiple output items. Therefore, the number of finished products is much larger than the number of input items. This paper addresses two important challenges in a real-life DPS problem faced by an aluminium manufacturing company. One challenge is that one product can be produced following different process routes that may have slightly different capabilities and capacities. The other is that the total inventory capacity is very limited in the company in the sense that a fixed number of inventory spaces are commonly shared by raw materials, WIP (work-in-process) items and finished products. This paper proposes a two-step approach to solving this problem. In the first step, an integer programming (IP) model is developed to plan the type and quantity of operations. In the second step, a particle swarm optimisation (PSO) is proposed to schedule the operations determined in the first step. The computational results based on actual production data have shown that the proposed two-step solution is appropriate and advantageous for the DPS scheduling problem in the company.