In this posting we will discuss Step 3 of the
Ultimate Improvement Cycle, Improve.
This step is where the rubber meets the road so to speak. To make it a bit easier for you to follow, let's repost the two UIC graphics I had posted on Focus and Leverage Parts 312 and 313.
Otherwise, you will continue building
inventory in front of your constraint, beyond your safety buffer. Subordinate
in its simplest form means that you will produce product at the same rate as
the constraint operation, no slower or faster.
According to Debra Smith, “Mastering step three, subordination, is the
key to succeeding with TOC. Mastery of step three is dependent on a methodology
of aligning measures, performance objectives, strategies, and policies to
support maximizing return on investment. Return on investment is centered on
understanding the interdependencies of the constraining resources and the rest
of the organization. I could not agree more with Smith, as subordination is
beyond a doubt one of the keys to the success of any TOC-based improvement
initiative.
Like step 2a, step 3a of the UIC is a
planning step, in that you must evaluate the nonconstraints and look for
opportunities where you might be able to offload some of the work from the
constraint to one or more of the non-constraints. You will look upstream and
downstream for these opportunities, so you must be very thoughtful and
methodical as you develop this plan. In doing so, however, you must exercise
caution in this step because you must make certain that you do not turn a
nonconstraint into a constraint, and you could, if you are not careful. In
addition, contrary to what many production managers believe, having a perfectly
balanced line (i.e., all cycle times equal) is not necessarily a good thing
(see Chapter 9).
In addition, you are attempting to establish
one-piece flow within your process to ensure the steady flow of work into and
out of the constraint. Because you have already implemented work cells in step
2b, in essence you may have already begun using elementary one-piece flow, but
in this step, you formalize it. Your plan will include an analysis of current
constraint and non-constraint cycles and processing times, telling you where
you might be able to move work away from the constraint; how best to move the
work; how best to create flow; how to establish a constraint buffer, an
assembly buffer, and a finished goods buffer as well as a buffer replenishment
system; what your resource requirements are; how to address your training
needs; and how to best time all of the proposed moves.
At this point, you might be wondering why you
did not perform this step of the cycle sooner. There are two reasons. First, my
belief is that because you know that the capacity of the constraint operation
will improve as a result of your waste and variation reduction actions
completed thus far, you should wait until your new constraint capacity and
processing time are known. The second reason is that the next step in the
improvement cycle could radically change the time in the constraint, and hence
the capacity.
In step 3b, you will focus your efforts on
reducing processing time and improving flow by executing part of the plan you
developed in step 3a. You have analyzed your upstream and downstream
nonconstraint workloads; decided what work, if any, can be safely moved away
from the constraint operation; developed or proposed redesigned process steps
to accommodate the unloading of constraint work; estimated the new processing
times for both non-constraint and constraint operations; and estimated the
impact on flow and throughput. If you did your homework correctly, you should
breeze through this step and move on to step 3c. Remember, the planning for
this step had already been completed in step 3a.
In step 3c you will optimize the constraint,
assembly, and finished product buffer and refine your DBR scheduling system
based on any problems you may have encountered in step 2b. You will analyze
your new data on compliance to schedule and, if need be, make any corrections
necessary to improve compliance. The buffer in front of the constraint
operation, sometimes referred to as a WIP cap, is your protection for the
constraint operation in the event that one of your upstream non-constraints
could unexpectedly have downtime. Keep in mind that your buffer is not
necessarily product. In fact, most of the time your buffer will simply be a
measure of time—that is, instead of having excess product available, your
production schedule will dictate when and how many parts to produce so that you
never starve your constraint.
The assembly buffer is a buffer of
nonconstraint parts in front of assembly, assuming the constraint part is
required in assembly. The finished product buffer is your protection for
on-time delivery to customers. In this step, you need to recalculate the size
of your protective buffers, taking into account the speed of the upstream
nonconstraints, the historical downtime associated with the non-constraint
operation, buffer penetration rate, and so on.
The important thing to keep in mind is that
your non-constraints have sprint capacity, that is, the capacity to produce
product at faster rates than your constraint operation; so if an upstream non-constraint
operation experiences downtime for some reason, when it begins producing again,
it should still have the ability to produce product at a fast enough rate to
resupply the constraint buffer before the constraint buffer runs dry. Assuming
you calculated the size of the buffers correctly and designed the DBR system
correctly, the constraint will be protected from ever sitting idle.
In my next posting, I will discuss the fourth
and final step of the Ultimate Improvement Cycle, Control. In this step we’ll discuss how to “keep” all
of the gains you’ve made to this point.
Bob Sproull
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