Page 307 - DMGT501_OPERATIONS_MANAGEMENT

Unit 13: Supply Chain Management and JIT

Notes
Figure 13.7: C-Kanban and P-Kanban

Each process (area, cell) on the production line has two Kanban ‘post-boxes’, one for C-Kanbans
and one for P-Kanbans. At regular intervals a worker takes C-Kanbans that have accumulated in
his process post-box, and any empty pallets, to the location where finished parts (components,
assemblies) from the preceding process are stored. Each full pallet has attached to it one or more
P-Kanbans which he removes and puts in the appropriate post-box belonging to the process that
produced the parts. The worker now attaches a P-Kanban to the pallet and takes it back to his
own process area. When this new pallet begins being used its C-Kanban is put back into the post-
box. At each process on the line P-Kanbans are periodically removed from their post-box and
used to define what parts and quantities to produce next. There are three rules that must be
followed:
1. No parts to be made unless P-Kanban authorizes production

2. Exactly one P-Kanban and one C-Kanban for each container
3. Only standard containers are used and they are always filled with the prescribed quantity
The number of kanban card sets required in a particular location can be calculated as:

K = (expected demand during lead time + safety stock)/(size of the container)
If rounding is necessary, K must be rounded up to the next highest integer.
Lean Manufacturing strives to maximize long-term profitability and growth. Kanbans help
simplify planning and to fine-tune production to meet changing customer demand of
upto ± 10%. The system requires planned monthly and weekly production schedules. Kanbans
simplify day-to-day flexibility, hence changes to the production schedule only need to be given
to the final assembly process and then automatically work their way back up the line.
Kanban systems can be tightened by removing cards or by reducing the number of parts on a
pallet. The effect will be to speed the flow through the process and hence reduce lead times.
However, it also makes the system more vulnerable to breakdowns and other causes of
dislocation. By identifying the areas within the line that are causing disruption, efforts can be
made to improve them. Thus, the overall efficiency of the line is raised by tackling the key
points.
A Kanban system is a pull system, in which the Kanban is used to pull parts to the next production
stage when they are needed; an MRP system (or any schedule based system) is a push system, in
which a detailed production schedule for each part is used to push parts to the next production
stage when scheduled. The weakness of a push system (MRP) is that customer demand must be
forecast and production lead times must be estimated accurately. The weakness of a pull system
(Kanban) is that following the Lean Manufacturing philosophy is essential, especially concerning
the elements of short setup times and small lot sizes.
Single Card Kanban systems: In a single-card Kanban system, parts are produced and bought
according to a daily schedule and deliveries to the user are controlled by a C-Kanban. In effect,
the single-card system is a push system for production coupled with a pull system for delivery
to the point of use.

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