全部版块 我的主页
论坛 新商科论坛 四区(原工商管理论坛) 商学院 运营管理(物流与供应链管理)
2776 1
2010-06-29
What Is Inventory Management?


By Dr. Hermann Gruenwald


Companiesused to measure their muscle by the size of their inventory. Bigger wasbetter. Vast warehouses filled to capacity ensured efficient assemblylines and guaranteed that, come hell or high water, production wouldnever stop. Who cared about carrying costs? They would be erased byincreased sales. But now that equation has changed.

Loweringinventories is one of the quickest ways to decrease working capitalneeds. Performance measurements, such as the old standby ROA (return onassets) and the newer EVA (economic value added), as well as othermeasures that gauge how efficiently capital is used, have become morecommon organizational drivers. In fact, many times an executive's bonusdepends, at least in part, on how efficiently capital is used. Couplethe drive for efficient capital use with the need to respond morequickly to changes in customer demand, with shorter and shorterorder-to-delivery cycle times, and you have a problem that ischallenging many organizations.

Leaner and MeanerInthe big picture, American business has succeeded in its quest to runlean. But almost all these gains in inventory reduction happened from1981 to 1991, and the past 10 years have not seen much improvement.Inventory as a percent of GDP held steady at 3.8 percent from 1992 to2000. Rather than being eliminated, inventory has been pushed down intothe lower reaches of the supply chain, from manufacturers to top-tiersuppliers to lower-tier suppliers. GM, for example, improved inventoryturns, a common metric that measures total cost of goods sold dividedby average inventory, and serves as a valuable indication of how oftena company sells out its inventory (the higher the better) - 55.2percent between 1996 and 2001. However, the company that supplies itstires, Goodyear, saw its inventory turns decline21 percent during that same time. In other words, lower-tier suppliersare left holding the bag for the big boys like GM and Wal-Mart.

Inventory Management TheoryInventory and the management thereof belong to everyone in the company but nobody wants to own it.
InventoryManagement is truly interdisciplinary and spans from financial andmanagerial accounting, to operations research, material handling tologistics. The following is a quick overview of InventoryControl/Management terminology and theory.


Reasons for Holding Inventory:
  • Inventory balances supply and demand
  • Inventory acts as a buffer between critical Supply Chain interfaces
    • supplier – procurement
    • procurement – production
    • production – marketing
    • marketing – distribution
    • distribution – intermediary
    • intermediary – user
  • Inventory allows for economies of scale in
    • Purchasing
    • Transportation
    • manufacturing
Thereare various reasons for holding inventory. Inventory acts as a bufferbetween supply and demand fluctuations and irons out supply chainsystem failures.
The smoother your supply chainoperates and the better you are able to forecast the less inventory youhave to hold, unless you gain some economies of scale in purchasing,transportation and or manufacturing.


Categories of Inventory
  • Raw Material Inventory
  • Work-in-progress Inventory
  • Finished Goods Inventory


Thereare three categories of inventory; too much in either may be a badthing unless you have reasons for it such as seasonality, productionruns, and prevention of stockouts or improvement of customersatisfaction levels.

Types of Inventory/Stock
  • Cycle stock
  • In-transit stock
  • Safety or buffer stock
  • Speculative stock
  • Seasonal stock
  • Dead stock


If demand and lead time is constant, only cycle stockis necessary. In transit inventory is usually accounted for on theplace of shipment as it is not available at the destination. In-transit stock can be reduced through faster modes of transportation. Safety or buffer stock is a result of uncertainty of demand and lead time. Speculative stock is inventory held for reasons other than satisfying current demand, often acquired to reach economies of scale or to generate seasonal stock. Dead stock includes items for which no demand has been registered and may become obsolete.


Inventory Management Conditions
  • Certainty
  • Uncertainty


Ina perfect world as described in business school text books and casestudies one manages in a world of certainty. And the best orderingpolicy can be determined by minimizing the total of inventory carryingcosts and ordering costs using the Economic Order Quantity (EOQ) model.

EOQ =
2PD

               √ CV
P = ordering cost
($/order)

D = annual demand
(number of units)

C = annual inventory carrying cost
(% of product cost)

V = average cost of one unit of inventory
($/unit)


This formula can be adjusted for volume discounts and incremental replenishment, as well as other conditions.

Mostof us don’t work in a place called perfect, and are facinguncertainties. Life ends up throwing monkey wrenches into theproduction of widgets. For those of you who love math look at theoperations management literature and you will find ways to calculatefill rates, safety stock, and standard deviation of replenishmentcycles.


二维码

扫码加我 拉你入群

请注明:姓名-公司-职位

以便审核进群资格,未注明则拒绝

全部回复
2010-6-29 14:18:28
Symptoms of Poor Inventory Management

    * Increasing number of backorders
    * Increasing cancelled orders
    * Increasing numbers of returns
    * High customer turnover rate
    * Large number of obsolete items
    * Periodic lack of storage space

You know you have a problem if your backorders continue to increase and at the same time you are faced with increasing cancelled orders. Reverse logistics may be tasking as well as your number of returns increase, and you end up loosing customers, while accumulating obsolete items which among other things may lead to lack of storage space. You may face these inventory symptoms, but the causes may be part of the bigger picture.


Ways to Reduce Inventory Levels

    * Lead-time analysis
    * Delivery-time analysis
    * Eliminate low turnover items
    * Eliminate obsolete items
    * Analysis of package size
    * Analysis of discount structure
    * Examine returned goods procedures
    * Measurement of fill rate by stock-keeping unit (SKU)
    * Analysis of customer demand
    * Improve forecasting
    * Improve Electronic data interchange with vendors/suppliers

The above mentioned ways to reduce inventory levels should be part of a system approach to improving Inventory Management


Inventory Management Systems/Analysis

    * ABC Analysis
    * Forecasting
    * Advanced Order Processing Systems
    * Enterprise Resource Planning (ERP
    * Electronic Data Interchange (EDI)
    * Knowledge Management (KM) Systems
    * Vendor-Managed inventory (VMI)

ABC analysis is a tool to classify items according to their relative importance/profitability (Category A items are more important than category B items, and so on). A distribution by value report usually forms the basis of an ABC analysis. Better sales forecasting and advanced order processing systems as part of a larger marketing plan will reduce inventory. And Enterprise Resource Planning (ERP) system such as SAP will eliminate stove pipes and information silos and contribute to information sharing along with a company knowledge management (KM) system. Top management may see Vendor-Managed Inventory (VMI) as a way to out-source the inventory problem. But one has to be careful as it requires a high degree of transparency and integration between the partners. Such a marriage may bring a lot of benefits during the honeymoon period but also may have a costly divorce lurking in the background.


Inventory is a poor investment alternative for cash, but imperative to achieve required service levels. Maintaining the appropriate levels and types of inventory is essential to providing quality, timely service and products to your customers. Preventing stock-outs without overstocking products requires a disciplined process and information system that can dynamically manage this balance. Two of the keys to optimizing inventories are to improve reliability and reduce variability in the supply chain to meet your customer's demand while being cost effective. To order just in time and just enough.



References

Arnold, T. and Chapman, S. (2004). Introduction to Materials Management 5th Ed.

Prentice Hall, Upper Saddle River, NY



Narasimhan, S., Mcleavy, D. and Billington, P. (1995). Production Planning and    Inventory Control 2nd ed. Prentice Hall, Upper Saddle River, NY



Plossl, G (1985). Production and Inventory Control: Principles and Techniques   2nd ed. Prentice Hall,  Upper Saddle River, NY



Stock, J. and Lambert, D. (2001). Strategic Logistics Management 4th ed. McGraw-Hill, NewYork, NY.



Tersine, R. (1994). Principles of Inventory and Materials Management 4ed. Prentice Hall, Upper Saddle River, NY
二维码

扫码加我 拉你入群

请注明:姓名-公司-职位

以便审核进群资格,未注明则拒绝

相关推荐
栏目导航
热门文章
推荐文章

说点什么

分享

扫码加好友,拉您进群
各岗位、行业、专业交流群