Scheduling in a flexible job shop with continuous operations at the last stage

Abstract

A special flexible job shop scheduling problem is presented. The problem has continuous-operation constraints at the last stages. A formulation of the problem is given and an integrated approach combining the simulation of production processes and the genetic algorithm is used to solve the problem. The processing paths of all jobs are decision variables and designed to be one individual in the genetic algorithm. The simulation with the reverse process flows evaluates the feasibility and fitness values of individuals. A satisfactory solution can be obtained after evolution. In order to improve the robustness, certain amounts of jobs are always kept in front of the machines at the last stages. Finally, the proposed approach is applied to one steel-making plant and compared with a hierarchical approach.

Keywords:

• scheduling
• flexible job shop
• simulation
• genetic algorithm

Acknowledgements

Note—This paper is a revised and expanded version of a paper entitled Scheduling in a Flexible Job Shop with Continuous Operations at the Last Stage presented at 15th ASIM Dedicated Conference Simulation in Production and Logistics, Paderborn, Germany, 9–11 October 2013.