Study On Inventory Decision-Making Models For The Manufacture And Recovery Hybrid System With Deterministic Demand

Due to the lack of resources, energy sources, and the increase of human cost, product recovery, an integration mode which recycles the material, the value-added of energy and labor, will be introduced into the traditional production system, which is a development trend. Product recovery has become an important countermeasure for the enterprises to sharpen the competitive advantage, decrease the production cost and tap the new sources of profit growth. Due to the inherent complexity and particular operation of inventory management in the hybrid system, the modification of the traditional inventory management theories and methods are required objectively. One important part of production operation management in the hybrid system is inventory management, whose crucial problems lie in inventory decision-making. On the stages of production and sale, the decision-making models on the hybrid system are formulated, which are based on problems such as the disposal of used products, the external effect of manufacturing and remanufacturing, finite recovery capacity, a large quantity of used products at the beginning of the planning horizon, non-zero recovery time and product devaluation. This study is done by the research clue, i.e. problem presentation, model formulation, model solution and example verification. The main work and innovation includes:(1) For the hybrid system, its concept, types and comparison with other inventory systems are investigated respectively. The literatures on inventory decision-making in the hybrid system with deterministic demand are reviewed and summarized.(2) Due to the limitation that current research assumes used products are all returned and all recovered, or partly returned and all recovered, and doesn't take the effect of backorders into account, it is assumed in this study that used products are partly returned and partly recovered, the disposal of used products occurs and shortage is permitted. Based on the reason of disposing used products and the impact of backorder, two types of inventory decision-making models on non-quality factors causing used products disposed off without service level constraints and quality factors causing used products disposed off with service level constraints under the (1,R) and (P,1) policies are investigated, and the second type of models are subdivided into ones of starting recovery operation when used products are accumulated to a specific number or a certain time, when the numbers of manufacture and recovery setup are positive integers and the theory of eliminant and the property of difference function are adopted, the simple algorithms are developed respectively to determine the optimal numbers of manufacture and recovery setup, and the lot-sizes of manufacture and recovery, the maximum shortages corresponding to manufacture and recovery cycles and so on. The results show that when other parameters remain unchanged, the optimal policy type is determined by the recovery ratio. The choice of proper service level will be helpful to decrease the total cost. Compared with the related studies, the models developed in this study are more general.(3) Due to the limitation that the literatures on the inventory decision-making of supply chains are mainly confined to the forward supply chains, and the majority of literatures on the coordination of manufacture and recovery operations in the hybrid system focus on the enterprise level, the (1,R) and (P,1) polices in this study are applied to the inventory decision-making of the manufacturer in the closed-loop supply chain system, for the retailer, the manufacturer, the supplier and the collector, the more general cost and profit functions are derived. When the numbers of manufacture and recovery setup are positive integers, the algorithms are developed respectively to determine the optimal system policy under the (1,R) and (P,1) policies in the completely decentralized decision-making case, and based on this algorithm, the algorithms are also given respectively to determine the optimal system policy in the completely or partly centralized decision-making cases. The results show that the optimal system profit corresponding to the completely centralized decision-making is greater than those corresponding to other decision-making structures. The key to increase the system profit lies in the decision-making coordination of the manufacturer and the retailer in the supply chains. Similarly, the key to the decision-making coordination between players lies in the establishment of a profit sharing mechanism. Furthermore, the evolvement of the return rate of used products will cause the optimal policy type changed. Compared with the related studies, the models developed are more general and the decision-making structures are more close to real situation in this study.(4) Due to the limitation that current research assumes that used products are all returned, non-recovery used products are disposed off at a constant rate, and the constraint that the numbers of manufacture and recovery setup are positive integers is not taken into account, it is assumed in this study that used products are partly returned and all meet recovery requirement, those which can't be recovered will be disposed off in the former time interval during the model cycle. Inventory decision-making models under the (1,R) and (P,1) policies are formulated, and the algorithms to determine recovery sequence and recovery ratio for each product is developed respectively. When the numbers of manufacture and recovery setup are positive integers, the algorithms are given respectively for every product to determine their optimal lot-sizes of manufacture and recovery and minimum total costs and so on. Compared with the related studies, the disposal manner of used products is changed, another policy type is applied to multi-product recovery and inventory decision-making is easier to operate in this study.(5) Due to the limitation that the assumption that the numbers of manufacture and recovery setup are known can't ensure that the total cost corresponding to the optimal policy is minimum, it is assumed in this study that the numbers of manufacture and recovery setup are unknown, two types of total cost models are formulated corresponding to two cases, i.e. the case that non-recovery used products are stocked until the end of planning horizon and the case that non-recovery used products are disposed off at the beginning of planning horizon, and the corresponding minimum total cost functions for different switching periods and the scope of the optimal switching period are derived. Finally, the simple algorithm to determine the optimal policy of planning horizon is developed. The results show that the optimal policies of two types of models are same when the switching period is given. However, the introduction of the disposal cost of used products and the variable costs of manufacture and recovery will change the optimal policy of planning horizon. Compared with the related studies, the total cost corresponding to the optimal policy in this study is lowest, and the procedure is more straightforward and easier to use. (6) Due to the limitation that recovery time is not taken into account when return products are recovered in batches in the current literature and the studies on the inventory decision-making on short-life cycle products mainly focus on the forward supply chains, for the long-life cycle products, the inventory decision-making models for return products with the fixed-period and fixed-quantity recovery are formulated in this study from the perspective of cost, in which the effect of recovery time is taken into account; for the short-life cycle products, the inventory decision-making models for return products with the fixed-period and fixed-quantity recovery are formulated in this study from the perspective of profit, in which the effect of product devaluation is taken into account. The sufficient conditions on the minimum of the expected average cost function and the maximum of the expected average profit function are given, and the solution algorithms to determine the optimal order and recovery policy are developed. The results show that for the long-life cycle products, the fixed-period recovery mode is preferable, and the proper extension of recovery time will be helpful to decrease the cost. For the short-life cycle products, neither the fixed-period recovery nor the fixed-quantity recovery dominates, and with the increase of product devaluation rate, the sale period is shortened, and order quantity and expected average profit are decreased. Compared with the related studies, the models developed are more general in this study, and the policy of order and recovery in this study is preferable.