Track: Operations Research

Abstract

The paper deals with a relevant scheduling problem associated with moulding injection machines. A footwear company, equipped with advanced automation machinery, faces true difficulties in planning the injection equipment production. It is crucial to respect delivery times without disruptions.

There are many conditions associated with footwear and technological issues to consider, such as the weekly demand for different models and sizes, which is major to satisfy them on time. The moulds for each size of a model and distinct available machines, with varying quantities of positions for the moulds, are other concerned matters. Changeover times, which occur when changing moulds, are critical. Stocks are also considered. The time horizon attains tens of weeks.

We developed an integer optimisation model with the objectives of minimising both changeovers and stocks. That initial model underwent a few simplifications, acceptable from a strategic and technological point of view, due to the impossibility of reaching admissible solutions. The new version can solve the real dimension problems optimally, those that matter. The paper describes one case, and the solution obtained.

The new approach followed, and the solutions obtained, are essential for the company, given the planning difficulties; moreover, the method may also be relevant for any footwear industry facing similar combinatorial optimisation problems.