Optimum stock levels for excess inventory items
针对过剩库存问题，提出了两个模型来确定经济上不合理的库存水平，并计算应保留多少库存用于常规使用、多少应以残值价格处置，帮助组织减少库存投资、改善利润。
Abstract Insufficient attention has been focused on the ubiquitous problem of excess inventory levels. This paper develops two models of different complexity for determining if stock levels are economically unjustifiable and, if so, for determining inventory retention levels. The models indicate how much stock should be retained for regular use and how much should be disposed of at a salvage price for a given item. The first model illustrates the basic logic of this approach. The net benefit realized by disposing of some quantity of excess inventory is depicted by the following equation: urn:x-wiley:02726963:joom245:equation:joom245-math-0001 This relationship can be depicted mathematically as a parabolic function of the time supply retained. Using conventional optimization, the following optimum solution is obtained: urn:x-wiley:02726963:joom245:equation:joom245-math-0002 where t 0 is the optimum time supply retained; P is the per‐unit purchase price; P s is the per‐unit salvage price; C is the ordering cost; Q is the usual item lot size; F is the holding cost fraction; and R is the annual demand for the item. Any items in excess of the optimum time supply should be sold at the salvage price. The second model adjusts holding cost savings, repurchase costs, and reorder costs to account for present value considerations and for inflation. The following optimum relationship is derived: urn:x-wiley:02726963:joom245:equation:joom245-math-0003 where i is the expected inflation rate and k is the required rate of return. Unfortunately this relationship cannot be solved analytically for t 0 ; Newton's Method can be used to find a numerical solution. The solutions obtained by the two models are compared. Not surprisingly, the present value correction tends to reduce the economic time supply to be retained, since repurchase costs and reorder costs are incurred in the future while salvage revenue and holding cost savings are realized immediately. Additionally, both models are used to derive a relationship to describe the minimum economic salvage value, which is the minimum salvage price for which excess inventory should be sold. The simple model, which does not correct for time values, can be used by any organization with the sophistication level to use an EOQ. The present value model which includes an inflation correction is more complex, but can readily be used on a microcomputer. These models are appropriate for independent demand items. It is believed that these models can reduce inventory investment and improve bottom line performance.