A ruthless depletion of inventory logically leads to a manufacturing line
with closely coupled stations, where each station begins work only when the
downstream station requires it. Thus inventory is pulled through the line
rather than pushed through it.
In this casebook, Schonberger presents descriptions of 26 JIT
implementations. The majority of the sites are in the U.S., with the remainder
in Asia. None of the cases are wafer fabs, although several assembly/test
facilities are included. Each case includes discussion questions (for
Schonberger thoughts on the questions, see œInstructor Manual to Accompany
World Class Manufacturing Casebook: Implementing JIT and TQC?. The casebook is
designed as a companion to Schonberger orld Class Manufacturing: The Lessons
of Simplicity Applied.?/P>
Kanban implementations have been attempted in a number of wafer fabs, but the
results have been decidedly mixed. In light of this, it seems worthwhile to
periodically review the original JIT literature, both for useful principles and
for explanations as to the difficulty of wafer fab implementation.
In terms of useful principles, Schonberger has a section on IT ratio
analysis?that is worth reviewing. In it, he discusses three ratios:
| Lead-time to work
content: This measure is widely used in wafer fabs, and is commonly referred to
as the ycle time multiplier?or -factor?(the ratio of actual cycle time to
raw process time). |
| Process speed to sales
rate: This measure is not often seen in wafer fabs (probably because it is most
applicable to assembly line layouts). It refers to the ratio of production rate
to consumption rate. For example, if an upstream tool is capable of 60 wafers
per hour while the downstream tool is only capable of 10 wafers per hour, the
process speed to sales rate ratio would be 6. The JIT goal is to drive this
ratio to 1, e.g. to achieve a perfectly balanced line. Theory-of-Constraints
advocates will necessarily disagree with this particular Goal. |
| Number of pieces to
number of workstations: This measure is not often seen in wafer fabs, but it
does offer useful insight. It is similar to the œlead-time to work content?
ratio, but viewed through a different window, namely counting inventory (in
wafers) and dividing by the number of tools. A high ratio indicates excess
inventory or numerous large batch tools (in either case, bad for cycle
time). |
In terms of JIT implementation difficulties in wafer fabs, a quick scan of
the 26 cases reveals the following:
| Most of the factories
surveyed were able to move equipment with relative ease. In wafer fabs, moving a
single tool (let alone many tools) is often difficult, with problems ranging
from utility support lines to regulatory permits. |
| Most of the factories
surveyed had relatively short manufacturing process flows, ranging in length
from 5 steps up to 25 steps. Most wafer fab process flows involve hundreds of
steps. |
Although these factors do not mean that implementing JIT/Kanbans in a wafer
fab is impossible, they do indicate there will be hurdles unique to wafer fabs.
And in any event, we may still profit from a thoughtful application of JIT
principles and concepts.
If you are interested in the history of JIT introduction to the US, this
book is for you. If you are interested in the details of JIT implementation, and
you don mind the dated nature of the examples, this book is a useful
reference. If you are interested in applying JIT to wafer fabs, you best keep
looking. Personally, we would like to see a follow-up to these cases, a JIT
reunion of sorts, to learn the fates of these 26 factories.
