Ameliorating 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 schedules