Page 87 - How To Implement Lean Manufacturing

68 Cha pte r F o u r

to Flow are detailed in Chap. 5, with a case study in Chap. 15.) For example, let’s review
a process running multiple products in which one of the steps is a large machine, say a
press, that must undergo changeovers between production runs. To avoid stopping the
process during a changeover, a buffer is built up both before and after the machine, so
the rest of the production process can continue to run while the press is undergoing the
changeover.
All the items in these buffers will arrive “too early” to be just in time. However,
considering all the options, creating a buffer is the least-waste-generating choice for
the process, so it was selected. This does not create the ideal system but it is the eco-
nomically practical answer. In every case, if it is not currently possible to eliminate all
inventory in a process, then the next best solution is to design a system with the min-
imum amount of inventory. The amount is calculated, and posted at the work station
as a maximum. Whenever the upstream process has produced that maximum volume
of inventory, the upstream process must stop production to avoid the waste of over-
production. Kanban is just one system that is used to avoid overproduction. Most
other systems used to minimize inventory are based on limiting the physical storage
space that the parts may occupy. This is simple and creates a very good visual man-
agement tool.
Lead-Time Reductions Lead-time reductions are the essence of waste reduction in Lean.
They give the process both the maximum flexibility and maximum responsiveness to
changes; especially changes in demand either in quantity or model mix. Read about
lead-time reductions in Chap. 5, with a specific case study in Chap. 15, which shows
how you can break through the obstacles to flow and significantly reduce lead time.
Leveling Leveling is spoken of in two terms. First, leveling is the concept to maintain a
consistent nonvariant rate of production over time. It is also a waste reduction tech-
nique called model-mix leveling, that calls for the simultaneous production of multiple
products, or models of a product, from a given production line. To do otherwise is to
create a batch in the system. We have already stated that Lean is a batch destruction
technique. In a perfect world, we should level production to the individual production
unit level. In practice, this often is not practical and sometimes not desirable. Conse-
quently, we will frequently level based on the packaging requirements. That is, if we
package 60 units in one carton, we will run 60 of that model and then switch production
to another model. For example, if a certain manufacturer produces 50 models of a given
product, all in equal volume, and he has the ability to run all 50 models, one piece at a
time, it would be easy to implement perfect model-mix leveling. However, let’s say he
packages 60 units to a box and the cycle time is 30 seconds, so it takes 30 minutes to fill
a box. If this operation is run with perfect leveling, then at the packaging station there
are 50 boxes being simultaneously filled, and every 25 hours a large batch of finished
goods needs to be transported. If, however, the process is leveled so that one box is run
at a time—this is called a “pitch”—then there is only one box at a time being filled. Quite
frankly, this system of producing one pitch at a time makes the downstream handling
more “level” and also makes the kanban system much easier to use. Considering the cur-
rent conditions, leveling to a pitch is normally the optimum for any Lean system.
Kanban Kanban is the revolutionary practice of using cards, for example, to smooth
flow and create pull in a Lean system. It is also a continuous improvement tool. The
cards represent and account for all the inventory in the system. By controlling the