Page 60 - How To Implement Lean Manufacturing

CHAPTER 3

Inventory and Variation

any early efforts at imitating Lean production focused on the Just In Time
(JIT) concept of inventory reduction. Here, we will explore why many of these
Mefforts failed and introduce why we have inventory, why we need inventory,
and the two key business reasons why we strive to reduce inventory. We’ll explore the
dynamics of inventory creation and its relationship to variation and dependent events,
including making the sample calculation for all three types of inventory. Finally, we will
discuss the powerful tool designed by Ohno called kanban.

Background
In the 1970s, it became clear to a select few that the Japanese, most notably Toyota, had
found a better way to manufacture cars, which caused a number of very interesting
things to happen. First, and most notably, the majority of the manufacturing world
went into a huge case of denial. This was heard as “that will work in Japan, but not
here” and a variety of other statements that could politely be said to have lacked
insight.
However, some with a little more insight, curiosity, and humility asked, “Could
there be something to this?” Well, from that small group came a series of efforts to try
to capture parts of the Toyota Production System that were serving Toyota so well. The
piece that seemed the most appealing was the JIT concept. It was rapidly popularized
as an inventory reduction effort, which in fact is only a part of what it really is.
JIT practitioners came out of the woodwork and many companies went about
implementing kanban and slashing inventories to reduce the high cost of producing and
managing the inventory. Some went about using the slogan of “Zero Inventory” and
slashed inventory with such fervor it was as if they were pursuing the Holy Grail of
manufacturing. Inventory had become a bad word, much like “scrap.”
Unfortunately, many of these efforts were grossly misguided. Their only focus was
on inventory reduction. They reduced inventories as if it were an independent entity
that had no relationship to anything else. JIT implementation efforts became nothing
more than aggressively slashing inventories. Those that had this approach often caused
irreparable damage. They found they needed to expedite nearly everything, needed to
work large amounts of overtime, and then still frequently missed delivery dates. Others
found the worst of all scenarios. They not only missed shipments but as they cut
inventories they found that production rates flagged significantly. Due to these mis-
guided efforts, many companies ceased to be competitive and some even went out of
business.

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