optimizing the safety stock with guaranteed service model in reverse logistics considering internal and external returns

In this paper, a guaranteed service model (gsm) is considered in a general supply chain with the releasing of the service time constraint. for this purpose, a bi-objective model is developed containing minimization of both service time and the holding cost of safety stock. in addition to considering the return of items from inside of the chain, the returns from outside of the chain are also considered to carry out remanufacturing, refurbishing, and repairing processes. the model is solved in a real-world case of the electronic product supply chain and the pareto solution set is obtained to show the changes in the holding cost of safety stock based on the maximum time for the different services offered to customers.