兩階層存貨系統安全存量配置最適化之研究－以半導體設備業為例

Abstract

由於半導體零配件的供應具有低需求､高成本､高服務水準及不可或缺的 特性﹐因此對半導體設備業而言，如何以較低的安全庫存，去滿足一定的 顧客服務水準，就成了最重要的課題。而本文就針對半導體設備業，構建 了一個在兩階段存貨系統中，滿足預先設定的顧客服務水準之下，關於安 全存量配置最適化的模式。在此模式中，引進了決策時間變數(decision time variable)的觀念去解決安全存量配置的問題。決策時間變數是一個 配銷中心安全存量的函數，由兩個部份所組成：一個是由地方倉庫(LW)到 配銷中心(DC)的前置時間(Leadtime)，這個部份是固定不變的；另一個部 份則是由配銷中心(DC)到製造中心(MC)的前置時間(Leadtime)，這個部份 則是會隨著配銷中心的安全存量而變化；而本文所提出的模式就是基於決 策時間變數的概念所構建出來的。經由實際數據的分析，可以得知此模式 可以提供一個較有效率的方法去解決有關安全存量配置的問題。而且，由 此模式中可以看出，降低從配銷中心到製造中心的前置時間是提升存貨系 統整體效率最有效的方法。 This research focuses on a two-echelon spare part inventory system in semiconductor equipment industry. The environment in this research is a world-wide semiconductor equipment manufacturer that supplies the demands from its distribution centers, and each distribution center supplies the demands from its local warehouses. Spare parts in semiconductor industry usually means those parts with high cost, high service requirement, and critical low demand. Almost every corporation in this environment adopts the continuous review ( S-1 , S ) policy because of the above characteristics. Therefore, the most important thing in this inventory control system is to determine the allocation of safety stock among the distribution center and its local warehouses. In this study, a decision time variable of local warehouse is introduced to find out the optimal allocation of safety stocks in this two-echelon inventory system. The decision time variable is composed of two parts. One is the leadtime from LW to DC. Another one is the leadtime from DC to MC, which is varied with the safety stock level at the distribution center. Based on the decision time variable, a new methodology to solve this kind of problem and procure the optimal allocation of safety stock is proposed. Although this proposed procedure focuses on the spare part inventory system, the same idea can be applied to solve the allocation problem in other inventory systems.