Optimisation conjointe des stratégies de production et de réutilisation en environnements incertains

Abstract

The work of this thesis is to elaborate joint optimal strategies of manufacturing, remanufacturing and maintenance of the production systems in the reverse logistics dynamic context. The manufacturing and remanufacturing processes are integrated into the model of stochastic optimization of manufacturing systems subject to random breakdowns and repairs of machines. An analysis of the degradation of the manufacturing unit according to its production rate is made. The availability of used products returned to the manufacturer and the differences in costs and performances of the machines justifies the development of a reverse logistics process. The contributions of this thesis are presented in four (04) phases: The first phase deals with the joint analysis of the optimal production and maintenance (repair and preventive maintenance) planning problems for a manufacturing system subject to random failures and repairs. The system consists of one machine producing one part type. When the machine fails down, an imperfect repair is undertaken. Thus, the failure rate depends on the number of failures. A two-level hierarchical decision making approach, based on the determination of the failure rates (first level) of the machine and the statement of a joint optimization of production, preventive and corrective maintenance policies (second level) is proposed. The optimization problem is solved by numerical methods. To illustrate the usefulness of our results, a sensitivity analysis was done. However, at this stage, the question of what happens when the machine is used to its maximum production speed for a long time has not been asked. The second phase of work permits to answer this question. To do this, we worked on the production planning of a manufacturing system consisting of two non-identical parallel machines producing one part type. The failure rate of the main machine (machine whose production rate is the higher) depends on its production rate. A model has been presented using a non-homogeneous Markov chain, and the numerical solution of the Hamilton-Jacobi- Bellman (HJB) equations has provided the solution for the manufacturing system. The results suggest that to obtain gains in availability of the main machine and to reduce the total cost incurred, it may be beneficial to decrease the production rate when the inventory level approaches the threshold value. This approach is very important in the case of manufacturing systems where the speed of production greatly influences the wear of the cutting tool (for example, in the metallic parts machining industries). Our results have been validated through a sensitivity analysis. Although phases (01) and two (02) provide interesting results, we could not conclude this work without exploring the aspect of reverse logistics. Indeed, nowadays, many companies remanufacture used products due to the rarity and cost of raw materials, environmental protection and environmental legislation. We considered this issue in the third phase. In the third phase, the second machine of the second phase is the machine of remanufacturing (reuse of recovered parts on the market). Thus, we study hybrid manufacturing/remanufacturing systems with the production-dependent failure rates of the manufacturing machine. By reducing the production rate of the manufacturing machine to account for its reliability, this machine is unable to satisfy the customer demand alone, which is why the remanufacturing machine is called upon to fill the demand. The objective of the system is to find the production rates of the manufacturing and the remanufacturing machines that would minimize a discounted overall cost consisting of serviceable inventory cost, backlog cost and holding cost for returns. The problem is solved by numerical methods. Sensitivity analyses are developed to show the relevance of the proposed approach. The fourth phase is the validation of the models developed on a practical case. We aim for companies which produce compatible cartridges, Laser and Inkjet, both new and remanufactured. Under reasonable assumptions, other industrial sectors such as automobile and aircraft assembly lines, manufacturing of mechanical parts can also benefit from the results obtained.

Date	24 Apr 2014
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Jean-Pierre Kenné (Supervisor), Victor Songmene (Co-supervisor) & Pierre Dejax (Co-supervisor)