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International audience; We consider a production-inventory system that consists of n stages. Each stage has a finite production capacity modelled by an exponential server. The downstream stage faces a Poisson demand. Each stage receives returns of products according to independent Poisson processes that can be used to serve demand. The problem is to control production to minimize discounted (or average) holding and backordering costs. For the single-stage problem (n = 1), we fully characterize the optimal policy. We show that the optimal policy is base-stock and we derive an explicit formula for the optimal base- stock level. For the general n-stage problem, we show that the optimal policy is characterized by state-dependent base-stock levels. In a numerical study, we investigate three heuristic policies: the base-stock policy, the Kanban policy and the fixed buffer policy. The fixed-buffer policy obtains poor results while the relative performances of base-stock and Kanban policies depend on bottlenecks. We also show that returns have a non-monotonic effect on average costs and strongly affect the performances of heuristics. Finally, we observe that having returns at the upstream stage is preferable in some situations.

International audience; This paper studies the coordination of manufacturing, remanufacturing and returns acceptance in a hybrid system. We use a queueing control framework, where manufacturing and remanufacturing are modeled by single servers with exponentially distributed processing times. Customer demands and returned products arrive in the system according to independent Poisson processes. A returned product can be either rejected or accepted. When accepted, a return is placed in a remanufacturable inventory. New products and remanufactured products are placed in a serviceable inventory and customer demands can be satisfied by new products or remanufactured ones. For a cost structure including holding, backorder, manufacturing, admission and rejecting costs, we show that the optimal policy is characterized by two state-dependent base-stock thresholds and one state-dependent acceptance threshold. We also obtain monotonicity results for these switching curves. Then we adapt several heuristic policies from the literature to our model. Finally we carry out a numerical study to compare their performances to the ones of the optimal policy.