عنوان مقاله [English]
One of the main and most important elements of supply chain management is the appropriate selection of proper suppliers in a manner which goes with the long term objectives of an enterprise or organization. The supplier selection problem is a multiple criteria decision making problem that is affected by various factors which are mostly conflicting. In a majority of commercial activities, such as supplier selection, the importance or weights of objectives and constraints are not equal for decision makers, and the criteria should be weighted subject to the specific status and situations of the purchasing activity. Moreover, it is impossible to determine input data clearly and deterministically in the real world. In such cases, fuzzy sets theory is one of the best tools to face the vagueness and impreciseness. Regarding former studies, the quality of products and raw materials has been considered a key criterion in supplier selection for the buyer, with respect to other factors affecting the decision-making process. In addition to the necessity of maximizing the quality level, considering an acceptable minimum level for quality seems to be essential in modeling the problem. Regarding this subject in the form of a constraint, helps to satisfy this issue persistently. Taking the acceptable quality level constraint imprecisely and having a fuzzy form is one of the new concepts explored in this research. Besides, in the real world, sellers often suggest a delay period in payment of goods sold to encourage buyers. In such situations, the buyers are able to take advantage of receiving their requests and not paying the cost, while the sellers lose the interest of their earning during this period. From the viewpoint of a buyer who selects the suppliers, minimizing the present value of the cost supposed to be paid is essential to be considered as an objective function in modeling the multi objective problem supplier selection. For the first time in the literature, this research tries to develop existing models in this context, regarding the delay in obtaining the payments of buyers and formulating it in the form of a NPV function, as well as considering the fuzzy constraint of an acceptable quality level for each supplier. This function points to the present value of money and must be minimized because of its cost nature. Also, the model is
solved utilizing multi objective programming techniques. Finally, the model is illustrated and solved in a numerical example.