Production scheduling with capacity-constrained transportation activities

This article presents a model for scheduling activities that are required to manufacture a product batch in a multistage process. The activities include setups, operations, and load movements between operations. In this model, setups may or may not require a unit from the preceding operation; each operation must be performed continuously on the batch once it has started, and capacity constraints apply to transportation activities. Within this context, two productivity-related objectives are sought. The primary objective is to minimize the total production time for the batch; the secondary is to minimise the number of load movements. The article develops a branch-and-bound routine to solve subproblems of scheduling transportation activities. The efficiency of this routine that results from exploiting the specific structure of the subproblems is critical for the success of the overall procedure. While the subproblems can be solved as zero-one mixed-integer programs, this approach is too computationally burdensome for all but the smallest of problems.