A heuristic to schedule flexible job-shop in a glass factory

We describe the design and implementation of a scheduling system in a glass factory. The factory produces a large variety of manufactured glass objects in a complex process ranging from melting the glass in the furnaces and blowing it automatically or manually to decorating, assembling and packing it. The structure basically corresponds to a flexible job-shop scheduling problem with some special characteristics. On the one hand, dealing with hot liquid glass imposes no-wait constraints on some operations. On the other hand, skilled workers performing some manual tasks are modelled as special machines. The system produces approximate solutions in very short computing times, trying to minimize a non-regular criterion defined by the user and based on due dates. It can be used to establish delivery dates for new customer orders, taking into account current machine workloads, or to schedule a set of orders, trying to meet given customer due dates.