Page 338 - Orlicky's Material Requirements Planning

CHAPTER 19 Repetitive Manufacturing Application 317

of inputs is balanced with the flow of outputs, the overall level in the river stays constant.
The water level in the river reflects the lead time through the plant and the inventory in
the operation. Since the lead time for a repetitive manufacturer is so short, the work-in-
process is very low. Critical feedback processes for the repetitive enterprise include the
ability to report production-rate variances in addition to the expected cost variances.
The repetitive sequential operations are directly related to each other, so if one oper-
ation stops, the balance of the line soon stops. Piles of inventory are not allowed to build
up between operations. This stable level of work-in-process simplifies the control and
reporting systems. True repetitive systems have rate-based production scheduling and
backflushing capability. This backflushing can occur at a pay point partially through the
routing or simply at the end of the process. The system does not create work orders in the
background. When a job shop system attempts to masquerade as a repetitive system, this
background creation of work orders is common practice. The creation and processing of
work orders in the background can consume a great deal of computer power and pro-
cessing time.
High volumes and very low variety characterize the repetitive product. The raw
materials needed are repetitious in quantity and timing. The end items are still discrete
but are produced in a very short cycle time, typically less than one day. Management of
this type of operation turns to balancing the capacity along the line rather than planning
detailed routings. The BOMs tend to be very flat. This means that they have very few lev-
els. Routings are simple, with only one or two steps, because the operations are closely
coupled with each other. The entire line is either running or not. The option of having
some work centers working while others are idle is not common in this environment.
Costs for this type of operation are easy to allocate directly to these focused lines.
The four-wall approach is used to track inventory. Receipts are transacted when the
product arrives, and deductions are made to the inventory when the final product leaves.
Intermediate tracking does not add value to the process, only cost, so such tracking is not
done. The traditional intermediate tracking is no longer required because the materials
are in process only for a very short period of time.

KANBAN
Just-in-time (JIT) execution tools are used to bring materials to the line very close to the
time of need, as in kanban. In actuality, kanban is a Japanese word that literally means
“sign board.” According to the American Production and Inventory Control Society
(APICS), a kanban is a “method of just-in-time production that uses standard containers
or lot sizes with a single card attached to each. It is a pull system in which work centers
signal with a card that they wish to withdraw parts from feeding operations or suppliers.
This is also known as a move card, production card, or synchronized production.” Figure 19-1
shows the actual Japanese kanji characters for a kanban system.
A kanban can be a light that signals replenishment, a card that is moved, an empty
container that is sent to the supplier to be filled when the active one is empty, or even a