Determining the number of suppliers chosen for cooperation in a supply chain is one of the most important problems in the supply chain management area. Regarding the fact that simultaneously decreasing the risk and cost is one of the most important objectives of every organization, besides the cost, the risk has also been introduced in the recent researches, as one of the most important criteria. In this paper, the decision tree approach is used for determining the optimal number of suppliers considering the supply risk and it has been tried to develop an applied method through expanding the cost criteria. The proposed model in this paper, therefore, contains any kind of cost ingredients such as cost of suppliers development, cost of suppliers management, cost of missing discount in volume due to increase in number of suppliers in supply base, and loss cost due to supply postponement from suppliers. This approach is implemented in Emersun Company.

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<p>This thesis presents the development of a novel model for solving the flexible job shop scheduling problem with maintenance activities where maintenance activities are limited by a maintenance crew constraint. Moreover, in order to extend it in terms of energy consumption, the cost of energy usage associated with different states of the machines is considered in the objective function. The objective is to minimize the total cost of hiring repairmen, energy consumption, and tardiness penalties. We assume the production machines in this environment may break down which causes the unavailability of the machines for the production. In the maintenance phase, a threshold-based maintenance strategy is applied based on the obtained optimal replacement age of each machine. Accordingly, the required maintenance action is divided into two categories: minimal repair or replacement activities. Furthermore, opportunistic maintenance is considered in the scheduling to minimize the required number of repairmen to be hired. In fact, the main aims are to find the optimal machine assignment and operation sequence, to determine if preventive maintenance is required to be executed between two consecutive operations, and to specify the optimal number of maintenance crew to be hired for the shop floor to minimize the expected total cost.</p>

<p>This thesis presents the development of a novel model for solving the flexible job shop scheduling problem with maintenance activities where maintenance activities are limited by a maintenance crew constraint. Moreover, in order to extend it in terms of energy consumption, the cost of energy usage associated with different states of the machines is considered in the objective function. The objective is to minimize the total cost of hiring repairmen, energy consumption, and tardiness penalties. We assume the production machines in this environment may break down which causes the unavailability of the machines for the production. In the maintenance phase, a threshold-based maintenance strategy is applied based on the obtained optimal replacement age of each machine. Accordingly, the required maintenance action is divided into two categories: minimal repair or replacement activities. Furthermore, opportunistic maintenance is considered in the scheduling to minimize the required number of repairmen to be hired. In fact, the main aims are to find the optimal machine assignment and operation sequence, to determine if preventive maintenance is required to be executed between two consecutive operations, and to specify the optimal number of maintenance crew to be hired for the shop floor to minimize the expected total cost.</p>