Towards an optimized leasing contract of a multi-machines system based on the integration of production and maintenance

La minimisation des coûts et la maximisation de la satisfaction du client sont les facteurs majeurs dans le développement des activités d'une entreprise. Ceci pourrait être assuré par les bonnes pratiques de gestion et de prise de décision à travers un processus de planification hiérarchique bien déterminé: Stratégique, tactique et opérationnel. Dans la plupart des cas, les industries manufacturières ont tendance à planifier la production de façon à minimiser les coûts et remédier à la pénurie des produits. Ceci permet à l’entreprise d'avoir une vision stratégique permettant d'optimiser ses activités sur plusieurs plans (maintenance, approvisionnement, qualité...). Mais pour assurer une meilleure optimisation et assurer la continuité de l'entreprise, les managers doivent joindre la maintenance à la production et les considérer comme des systèmes interdépendants. Dans ce contexte, plusieurs travaux ont traité le cas de maintenance intégrée à la production et l'ont considéré comme outil d'optimisation afin de minimiser les coûts et assurer une certaine compétitivité. Des travaux ont aussi intégré la dégradation des machines pour planifier les actions de maintenance. Cependant, la production et la maintenance sont liées à diverses ressources physiques (ouvriers, machines etc..) que l'entreprise doit prendre en considération. Autrefois, les industries ont toujours tendance à se procurer toutes sortes de ressources physiques afin de satisfaire ses demandes. Ces ressources sont alors toujours disponibles, même si elles sont inutilisées pendant certaines périodes de production. Ayant conscience des pertes que peut causer ces ressources en cas de non utilisation, certaines entreprises choisissent de sous-traiter ou de louer quelques ressources pendant une période donné afin de satisfaire une demande bien déterminée. La particularité de notre travail consiste à trouver la quantité des ressources à louer afin de satisfaire la demande. En effet, en s'inspirant du modèle HMMS, qui étudie la planification de la production et des stocks en prenant en considération la variation de nombre de ressources humaines travaillant, on a eu l'idée de transformer le problème et de chercher alors le nombre optimal de machines à louer pendant chaque période. Ayant conscience aussi de l'importance de la planification de maintenance, celle-ci a été intégrée au plan de production afin de trouver la meilleure solution. Le nombre de machines à louer étant variable, on a considéré qu'il varie selon la demande des clients. Des stratégies de maintenance améliorées ainsi que de nouvelles contraintes ont été prises en considération lors la planification des plans de production et de maintenance du système étudiéAmeliorating the situation of an industry requires certainly reducing costs and maximizing the customer satisfaction. These two goals can't be achieved without a good management and a good knowledge of making decision tools. These decisions are generally associated, at least, with three levels of the hierarchical planning process: strategic, tactical and operational levels. Generally, manufacturing industries aims at determining the most adequate production planning which helps them to minimize costs and hedge against capacity shortages. Releasing such an efficient planning urges firms to have a global vision on their production process which may be looked upon as an inter-dependant set of sub systems performing various functions including ordering raw materials, assembling pieces, controlling quality, repairing machines, storage, etc. But, it is worth mentioning that to ensure the continuous productivity of a firm, managers have to focus especially on both production and maintenance sub-systems and consider them as strongly dependent systems. In this context, many researches were carried out in industrial field dealing with joint production and maintenance planning optimization as a solution to minimize costs and guard against important competitiveness. Such an optimization may be more efficient when considering the degradation of workstations over time while scheduling maintenance actions. Moreover, production and maintenance activities deal with diverse physical resources including mainly workforce and workstations. So, it is worth noting that, while making decisions and proposing planning, a special attention should be made on the manner of managing these resources which remain indispensable for the firm's sustainability. Previously, firms used to buy (and recruit) all physical resources required to fulfill orders. So, these resources are always available at the industry even if they are sometimes more and less needless and useless during some production periods. This may take place especially when the firm has to fulfill fluctuating demand causing consequently drastic costs. Aware about the superfluous costs of possessing, for a long period, resources which can be sometimes pointless, subcontracting and leasing have become very important for many manufacturing firms because of the advantage that these solutions can bring. So, nowadays, these industrial solutions are becoming more and more in vogue concerning mainly subcontracting workforce to perform some tasks (maintenance, supervision, audit,...) or leasing workstations in order to produce the required quantities. In the present work, we deal with a new concept, that no previous work has dealt with, consisting on leasing machines depending on the ordered quantities. In fact, inspired mainly from the HMMS model, carried out by a group of economists who studied the production, inventories and workforce planning considering variable number of human resources, we had the idea to transform the problem from a workforce planning problem to a workstations planning one. Also, aware about the drastic importance of managing the production and the maintenance planning simultaneously, we aim in the present work at suggesting a joint production and maintenance planning optimization under leasing constraint. Otherwise, in our work, dealing with many leased machines, we consider that the number of these used machines does not remain constant and may vary from a production period to another depending on a fluctuating demand over a finite time horizon. Moreover, in the present work we aim at performing a disturbance analysis and to study its contribution to the development of conjugated production and maintenance planning considering leasing constraint and taking into account used machines degradation. Improved maintenance strategy and related constraints are also studied in this work in order to obtain optimal production and maintenance schedule