Page 67 - How To Implement Lean Manufacturing

48 Cha pte r T h ree

Buffers
Whenever there is variation, we need inventory to compensate for the variation if we
wish to maintain the production rate. This is not quite a true statement. Specifically, when
we have variation, we need something to compensate for this variation, to maintain rate.
We talk about inventory as being a countermeasure for variation, but in a more general
sense we need a buffer. A buffer is some resource we have in excess that is designed to
account for the fact that production cannot be in perfect lock-step with consumption.

Buffers come in three forms:
@
• Inventory
• Capacity
• Time

There are three types of buffers: inventory, capacity, and time.

• Finished goods inventory is a buffer because we must accumulate finished
goods between customer pick ups. WIP inventory is a buffer. It is a natural response
to variations in the production system, including scrap production, machine
downtime, changeovers, and cycle time variations, to name just a few.
• Excess rate capacity in a machine that requires changeovers is a buffer, a capacity
buffer.
• When we do not have a good understanding of our lead times—which for the
sake of argument vary from three to five days—we may enter a time buffer of
six days into our planning program to make sure that when we release an order,
it will be completed on time. In addition, a typical lean strategy is to run a plant
2 to 10 hour shifts. This strategy coupled with a some overtime, provides both
a time buffer and a capacity buffer.

Kanban

Basics
Kanban means sign board. A kanban can be a variety of things, most commonly it is a
card, but sometimes it is a cart, while other times it is just a marked space. In all cases,
its purpose is to facilitate flow, bring about pull, and limit inventory. It is one of the key
tools in the battle to reduce overproduction. Kanban provides two major services to the
Lean facility.
• It serves as the communication system.
• It is a continuous improvement tool.

Types of Kanban
Kanban provides two types of communication. In both cases, it gives the source, destination,
part number, and quantity needed.