ارزیابی انعطاف پذیری زنجیره تامین با محدودیت تعداد سفارش و فروش از دست رفته

In a flexible supply chain buyers and suppliers are willing to accommodate the uncertainties and variations in each other's businesses. In many instances the buyer may prefer to use supply flexibility, as opposed to an inventory holding strategy, to counter demand uncertainty. We consider the case where the buyer releases a fixed period replenishment order to the supplier under a supply contract defined by three parameters: (i) supply price per unit (ii) minimum order quantity and (iii) order quantity reduction penalty. Following a demand drop the buyer therefore has two flexibility options in the order cycle: (i) to place an order less than the supplier specified minimum order quantity and pay the associated penalty, or (ii) place no order and lose the sales for the current period. There is no penalty for not placing an order. A key buyer decision then is Qlost, the order or replenishment quantity level below which no order is placed and the sales are lost. A model for deriving the expected supply and lost sales cost as a function of Qlost is presented, and it is shown that the optimal value of Qlost is the inflexion point of the lost sales cost and the quantity penalty. The model is then used to select the supplier that minimizes the procurement plus lost sales costs from a given set of supply bids and a known expected customer demand behavior. Finally, the buyer also has the option to make capital investments in the supplier so as to reduce the minimum order quantity and hence reduce the projected supply costs. We evaluate the economics of this tactic.

Modern supply chains demand a flexible supply relationship between buyer and seller. In many instances the demand for the end product is highly uncertain. In such cases the buyer may prefer to use supply flexibility, as opposed to an inventory holding strategy, to counter the demand drop. Frequently, though, the unit supply cost is penalized as a function of the decreasing order quantity. Das and Abdel-Malek (2003) define supply chain flexibility as the robustness of the buyer–supplier relationship under changing supply conditions. A highly flexible relationship is one in which there is little deterioration in the procurement cost under different supply conditions. In a flexible relationship the supply contract allows the buyer to transmit some of the adverse effects of customer uncertainty to the supplier. This results in a reduction in inventory risk for the buyer. A good supply contract must therefore be robust enough to provide sufficient flexibility and should permit economic component supply for both parties in all possible market scenarios. Das and Abdel-Malek (2003) observe that supply relationships are prone to deteriorate as demand uncertainty increases, since one or both parties attempt to violate an inflexible contract. They identify two common cases of buyer requests when demand is uncertain: (i) a short lead time order shipment following a demand surge, and (ii) a smaller than normal order quantity following a demand drop. They presented a model for estimating the supply or procurement costs for a given supply contract with these requests. They assume the buyer demand is known to be normally distributed, and from this they are able to derive the likelihood of each request occurring and the associated cost penalty. They extended their model to select the best supplier for a specific product when there are several candidate suppliers. The selection objective was to minimize the expected annual procurement costs. This paper considers case (ii), which is following a demand drop the resulting order quantities are much smaller. We assume the buyer places replenishment orders to the supplier once in each fixed period. The buyer can also choose not to place an order and there is no penalty for this. Under low demand conditions the buyer therefore has two flexibility options in the order cycle: (i) to place an order less than the supplier specified minimum quantity and pay a quantity penalty, or (ii) place no order and lose the sales for the current period and accept the lost sales penalty. The two penalty functions are inversely related; hence as demand drops below the minimum quantity, the buyer will first opt for option (i) then if the demand drops further the second option is more attractive. The second flexibility was not considered by Das and Abdel-Malek (2003), and in effect the penalty increased monotonically as the order quantity decreased. Here both flexibility options are considered, and the demand point where the switch occurs is derived. Note that there is a third option in which the buyer places an order equal to the supplier specified minimum quantity. In this option the buyer avoids both penalties, but exposes itself to an inventory risk. We assume that the buyer has already decided that this is not an efficient option. Companies are increasingly convinced that when demand drops it is better to lose the sales rather than expose the supply chain to substantial inventory risk and discount pricing. We define as Qlost the demand or order quantity level below which the buyer opts not to place a replenishment order and accepts the lost sales. In this paper we develop a model for deriving the expected supply costs plus lost sales cost as a function of Qlost. We show that the optimal value of Qlost, in the context of the annual procurement cost, is simply the inflexion point of the lost sales cost and the quantity penalty. The model is then used to select the supplier that minimizes the procurement plus lost sales costs. This assumes there are a given set of supply bids and a known expected customer demand behavior. The supply bid is the supply contract proposed by each of the candidate suppliers. The contract specifies the minimum supply quantity above which there is no cost penalty, and the cost penalty function below the minimum quantity. Once a supplier is selected, then additional collaborations may occur between buyer and supplier in an effort to increase the supply flexibility. One common tactic is capital investment in the supplier facilities, these may be used to reduce setup costs or purchase more efficient equipment. The buyer offers to pay for these investments, and in exchange the supplier offers to reduce the minimum order quantity. We present a model for evaluating the economics of this buyer investment.