【物流英文】既然需要库存，为何还要加以控制？

海之月

As described in my previous post on The Hidden and Not-So-Hidden Costs of Inventory, simply having an inventory costs you between 30% and 65% of your inventory value per year. The main causes are:
就像我在前一篇文章《隐性及非隐性库存成本》中所描述的简而言之，每年的库存成本会占到库存价值的30-65%。主要原因如下：

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-Cost of capital
资金成本

-Taxes and insurance
税收和保险

-Storage cost
存储成本

-Handling cost
搬运成本

-Administration
管理

-Scrapping and obsolescence
报废及将要报废

-Deterioration and theft
变质和失窃

-Cost of delayed response time
响应时间延迟

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Probably the most underestimated one is the cost of delayed response. The lead time increases proportionally with the inventory. This relation is known as Little’s Law. The more inventory you have, the more sluggish your system becomes.

最可能被我们低估的就是响应时间延迟的成本。交货期与库存成比例增加。这种关系被称为利特尔法则。库存越多，系统就会越发迟缓。

○It takes longer for an order to be produced and delivered to a customer.
订单的生产和交付给客户，需要更长时间。

○If a downstream station detects defects, more parts have to be fixed or scrapped.
如果后道工作站/机台检测到缺陷，则必须修理或者报废更多的零件。

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○If there are product changes, it will take longer to flush out the old parts in the system (or you have to throw out more).
如果有产品发生变化，清理系统中的旧零件需要更长时间（或者必须扔掉更多的零件）。

○Generally, any change in production will take longer to become effective.
一般来说，生产中的任何变更都需要更长的时间才能生效。
What is a Good Trade-Off between Too Much and Too Little?
在库存上，太多和太少的权衡是什么？

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From the above discussion, the goal is clear. You should have an inventory that is large enough for your system to function properly, but not too large with the costs outweighing the benefits. The problem is finding this sweet spot. Manufacturing is usually a complex system with many different influences. It is all but impossible to determine this sweet spot theoretically. Rather, you have to find it by lowering your inventory and observing how your system reacts. On a side note, the typical status in many Western companies is, in my point of view, too little inventory rather than too much if the abilities of the system are taken into account.

以上的讨论，目标很清晰。我们应该有一个能让系统能够正常运行的足够大的库存，但是不要太大，因为那样，成本会大于收益。问题是要能找到最佳的度。伴随着诸多不同的印象因素，制造业通常是一个复杂的系统。理论上几乎不可能确定这个最佳的度。相反，我们得通过降低库存和观察系统的响应来找到这个最佳的度。另一方面，依我之见，许多西方公司的典型情况是，如果考虑到系统的能力，库存会太少而不是太多。

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Another complication but also opportunity is that the manufacturing system is not static. You can improve it and allow it to function with less inventory. You can also let it slide, resulting either in worse performance or a higher inventory needed, or both.

另一个难题，同时也是机遇的是制造系统不是静态的。你可以改进制造系统，让它以较少的库存运行。当然，你也可以对制造系统置之不理，这样做，要么导致绩效更差，要么会需要更高库存，或者两者兼而有之。

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Summary 总结
总结



Inventory is necessary to buffer fluctuations, for batching, and (last but not least) to actually have something to work with. Yet, too much inventory will not only increase cost, but also worsen a lot of other measures related to lead time. You would need to find a trade-off in the middle between. In my next post I will talk about the effect of simply reducing inventory without addressing these underlying reasons, and describe in more detail sensible ways to reduce inventory. Until then stay tuned and organize your industry!

对于缓减波动，库存是必要的，对于分批次处理和（最后但不是最不重要的）实际有一些事情需要去处理。然而，过多的库存不仅会增加成本，而且会让许多与交货期相关的其他措施变得恶化。你需要在两者之间找到平衡点。

Q168

The Hidden and Not-So-Hidden Costs of Inventory《隐性及非隐性库存成本》