Page 138 - How To Implement Lean Manufacturing

How to Do Lean—The Four Strategies to Becoming Lean 117

make one” system. Operationally in pure pull systems, it means you do not send
anything anywhere. If it leaves, someone came to pick it up. However, it is not pos-
sible to have a pure pull system in all cases. Wherever there is inventory, this inven-
tory will delay the pull signal from the customer. This is the basis used in kanban
design.
In kanban, the kanban card, for example, is removed from the product as product is
consumed. The card is then placed in a kanban post and the kanban card is then trans-
ported back to the heijunka board to signal replenishment. Second, since we can not
always use pure pull signals, the pull signals need to be time responsive to the needs of
the customer. The time it takes—from the receipt of the signal by the customer (product
is removed and the kanban card is placed in kanban post) until the replacement product
arrives at the storehouse—is called the replenishment time. This is effectively “pull
signal delay.” We strive to minimize pull signal delays. Simply stated, we work to min-
imize replenishment time.
The perfect pull system is “take one, make one.” For more information on replen-
ishment time, refer to Chap. 3, the section “Finished Goods Inventory Calculations”
and Fig. 3-1. The opposite of a pull system is a push system. In a push system, product
is made at an upstream station and then “pushed” to the downstream station indepen-
dent of the need of the downstream station. Push system allows local machine optimi-
zation at the expense of overall system optimization. They overproduce and create not
only excess finished goods inventory but excess WIP also.
Tools Used
• Kanban is the second most important tool used in creating a pull system. The
most important tool is training. It is critical that all employees understand the
concept of pull production. For example, in a close coupled manufacturing cell,
there are no kanban cards, but pull is practiced fully.
• JIT (Just In Time), support of all types, especially JIT staff planning support.
Wastes Reduced
Overproduction and inventory (in the form of WIP) is reduced.
Summary of Pull-Demand Systems
In most pull-demand systems, we will establish a signal to produce and then work to
reduce the time in the replenishment cycle.
Almost surely, if you have central planning or even a local MRP program designed
to do the scheduling, this will need to be altered. This will be a huge cultural change. To
bypass this planning step is normally not very hard technically, but it must be done
carefully since you will uncover all kinds of non-Lean activities going on. You will find
that the planning program does not work as designed and requires a great deal of
human interaction to make it work. This human interaction is often just variation by
another name.
The first thought most engineers have is to implement kanban, or rather the first
thought should be training. It will be a huge cultural change to get people out of the
practice of delivering. It may be some time before you can set up good delivery loops
with materials handlers to take care of WIP. Consequently, often in the early stages of
implementation, operators are still moving goods from one station to the next. This
needs to be changed from delivering to picking up.