應用6-Sigma DMAIC方法改善公司零配件庫存管理

Abstract

如我們所知，6-Sigma是由Motorola公司在二十多年前所發展出來的。而今天6-Sigma已經廣泛地應用在全世界幾乎每一個產業，做為許多公司改善缺點、精進製程之用。此外，我們亦瞭解，DMAIC是6-Sigma中的二大執行方法之一，主要用來改善公司既有的營運流程。其中，由DMAIC的五個流程—定義 (Define)、評估 (Measure)、分析 (Analyze)、改良 (Improve) 和管控 (Control)，我們可以很有系統地經由資料搜集及問題評估、分析，進而發展出一個有效的解決方法，達到長期管理公司經營的目標。 而有關存貨，它是公司或工廠經營時所必定會產生的營運項目。公司或工廠的存貨存在於不同的形態，由原物料 (Raw materials)、再製品 (Work in process)、成品 (Finished goods)、零配件 (Spare parts) 及辦公室雜項用品 (Office supplies)。雖說過多存貨會造成公司、工廠財務上的壓力及負擔，然而為提供客戶較好的服務品質，適量的庫存卻是絶對必要的。因此，提高客戶服務滿意度及降低庫存成本是存貨管理的二個主要目標。同時，儘可能地利用現有的資源，以最經濟的庫存管理營運成本來達到同樣的客戶滿意度並同時維持低庫存，亦是存貨管理的另一重要目標。在每一本存貨管理的教科書，都有記載基本存貨管理的理論及方法，用來管理上述公司、工廠內部的各種存貨項目。 而在公司的各種存貨中，零配件的採購金額雖然遠低於原物料的金額，然而，零配件卻是其中最複雜且差異性最大的項目。同時，雖然一般教科書有描述許多管理零配件等獨立需求 (Independent demand) 項目的方法，然而，在現實環境，尤其是大型公司、工廠，針對來到自國內外上萬種的零配件項目，這些方法，大部份過於理論或過於簡化，以致並未能有效解決現實營運中所面臨的複雜問題。而這也就是為什麼許多公司仍然必須發展出一套針對自己公司特質的存貨管理方法，來管理這些零配件等獨立需求的項目。 本文即是將6-Sigma的DMAIC方法應用於公司管理零配件等獨立需求項目的存貨管理方法的發展，並經由一實際的工廠成功案例得到印證。

As known in the world, 6-Sigma was developed by Motorola more than 20 years ago. Today, almost in each industry, 6-Sigma is still widely used in lots of companies in the defects elimination & process improving. Also known, DMAIC is one of two key methodologies of 6-Sigma & to be used in the existing business process improvement. From it’s 5 steps processes - Define, Measure, Analyze, Improve & Control, we can systematically go through data collecting, problems measuring then finding out process defects and developing the efficient solutions. About inventories, they are the must operational elements in each company and existing with different kinds of inventory types - raw materials (RM), work in process (WIP), finished goods (FG), spare parts & miscellaneous supplies. Although too much inventories would cause company dropping into poor finance situation, yet proper inventory is definitely needed to provide minimum or even better customer service. Therefore, the inventory management goals are to meet both higher customer service & lower inventory cost targets. At the same time, try to use the most limited resources, i.e., lowest operations cost, to reach above customer service & inventory cost dual targets. From every textbook, there were some inventory control solutions, methodologies & systems developed to manage mentioned each kind of inventories. Among these inventory types of items in a company, we know spare parts’ items characteristics & demands patterns are absolute the most variant & complicate type – even though their total purchasing values are much lower than raw materials spending. Meanwhile, although some existing independent demand inventory systems used for spare parts inventory management, yet in the real world, for many companies - especially the large scale manufacturing companies, sometimes, these textbook described systems are too theoretical or simplified to be used in solving practical but complicate cases. That’s why most of companies still need to design & develop their own modified systems to meet their unique environment & requirements. And, 6-Sigma DMAIC methodology would be the perfect solution to do the existing system assessment, measuring, improving and developing. In this thesis, I just applied this strict 6-Sigma DMAIC methodology to make improvement for company’s spare parts inventory management. It is a real case study that described the spare parts management system developing progress by following DMAIC steps in each involved department.