مدل تولید - موجودی یکپارچه با یک فروشنده و چند خریدار : مورد 'محموله سهام'

In recent years, companies have strengthened their supply agreements, and even the management of their inventories. To this aim, vendor-managed inventory (VMI) represents an interesting approach to stock monitoring and control, and it has been progressively considered and introduced in several companies. The research proposed investigates the way how a particular VMI policy, known as Consignment Stock (CS), may represent a successful strategy for both the buyer and the supplier. The most radical application of CS may lead to the suppression of the vendor inventory, as this actor uses the buyer's warehouse to stock its finished products. As a counterpart, the vendor will guarantee that the quantity stored in the buyer's warehouse will be kept between a maximum level and a minimum one, also supporting the additional costs eventually induced by stock-out conditions. The buyer will pick up from its store the quantity of material needed to meet its production plans and the material itself will be paid to the buyer according to the agreement signed. In previous studies, Braglia and Zavanella [2003. Modelling an industrial strategy for inventory management in supply chains: The ‘Consignment Stock’ case. International Journal of Production Research 41, 3793–3808] developed an analytical model of the CS policy, referring to a single-vendor and single-buyer situation. The same authors presented a comparison with the optimal solution available in the literature (in particular, with reference to Hill's model [1997. The single-vendor single-buyer integrated production-inventory model with a generalised policy. European Journal of Operational Research 97, 493–499]). The analytical results obtained allow the identification of the benefits and profitability that the CS approach determines in environments affected by uncertain demand. In order to understand the potential benefits of the CS policy, an analytical model is offered with reference to the interesting industrial case of a single-vendor and multiple-buyer productive situation, thus obtaining the optimal replenishment decisions for both the vendor and buyers in such a situation. The results show how the CS policy works better than the uncoordinated optimisation.

The present study makes reference to an industrial practice concerning the strategic management of inventories, known as Consignment Stock (CS). Initially, the authors observed it in a company manufacturing components for the automotive chain (Valentini and Zavanella, 2003; Braglia and Zavanella, 2003). This management strategy spread out rapidly in different manufacturing environments, confirming its strategic interest for companies and its positive attitude in being implemented in supply chains. However, the industrial implementation of CS agreements frequently requires the solution of some problems perceived by the two actors of the chain. In particular, 1. it is common opinion that the buyer gets the most advantages from the CS agreement, in particular when it is a large company interacting with a small–medium-sized vendor (supplier); 2. the vendor is frequently doubtful about the real advantages offered by the CS agreement, as he generally provides the same component/device to different customers and, therefore, he is unable to clearly perceive the real impact of the CS policy on his lot-sizing strategy. The former opinion may find a further support in the need for a continuous exchange of digital information between the two actors, which generally introduces the topic of a uniform information system. Such a change may be costly for a small–medium company (in terms of personnel, too) and the opportunity of a partnership with the larger buyer may be unavoidable. The second concern refers to a situation that is extremely common in practice, e.g. when the vendor is a component or raw material manufacturer and his customers are assembly companies or manufacturers. Such a problem suggested the present analysis, which aims at investigating the single-vendor and multi-buyer environment so as to draw some managerial indications useful for understanding whether the CS policy may be successfully implemented in pyramidal chains. According to the topics outlined, Section 2 offers the framework of the literature, so as to correctly locate the contribution in the scientific scenario. Section 3 presents the model notation and the assumptions introduced, while Section 4 focuses on the specific problem (single vendor and multi-buyer), introducing the notation and the model developed. Finally, a numerical example is proposed to validate the model and draw the managerial issues that it addresses (Section 5), and a sensitivity analysis is carried out to explore the influence of the relevant parameters (Section 6).

The present study aimed at proposing a model for a single-vendor multi-buyer system, integrated in a shared management of the buyers’ inventory, so as to pursue a reduction or the stability of the holding costs while descending the chain. The inventory management is carried out according to the CS practice and, consequently, the model extends the results offered in Braglia and Zavanella (2003). The model appears to be simpler than the analytical model developed by Siajadi et al. (2006), which is, however, based on Hill, 1997 and Hill, 1999 assumptions and consequently suitable for a supply chain with holding costs increasing while descending the chain itself. The results show that the joint management of the inventory gives rise to economic benefits, which, however, may be modest or relevant according to the structure of the chain. The results themselves suggested the development of a sensitivity analysis, which allowed drawing some interesting remarks on the influence of the parameters relevant to the economic performance of the supply chain (Section 5). The expected extensions of the study refer to • the analysis of batches of different sizes (as for the single-vendor single-buyer model proposed by Hill and Omar, 2006); • the analysis of the lead-time effects; • the implementation in the model of stochastic demand, so as to appreciate the benefits introduced by the CS approach with respect to the classical inventory management agreement between the actors of the chain. However, the most significant improvement of the study is represented by the analytical study of the influence of the problem parameters on the cost savings, which should be able to allow the full understanding of the system behaviour and of its features, as perceived in Section 6 devoted to the sensitivity analysis.