Page 88 - How To Implement Lean Manufacturing

Lean Manufacturing Simplified 69

number of kanban cards, we control the inventory. Kanban is a technique used to control
inventory, minimize overproduction and facilitate flow. The kanban cards are used to
trigger replenishment. This will make the system more responsive to customer demand
and shorten lead times because the signal comes directly from the customer and trig-
gers replenishment. For a kanban system to be effective, all kanban rules must be rigor-
ously followed. The Six Rules of Kanban, from Toyota Production System, Beyond Large-Scale
Production (Productivity Press, 1988), are:
• Later process picks up the number of items indicated by the kanban at the earlier
process.
• Earlier process produces items in a quantity and sequence indicated by the
kanban.
• No items are made or transported without a kanban.
• Always attach a kanban to the goods.
• Defective products are not sent on to the subsequent process. The result is 100
percent defect-free goods.
• Reducing the number of kanban increases their sensitivity.

Cells Cells are work areas that are arranged so the processing steps are immediately
adjacent to one another. This lets parts be processed in near-continuous flow either in
very small batches or in a one-piece flow. This, in turn, allows minimization of the
wastes of transportation and inventory—in this case, WIP (work in process). The most
common shape is the “Inside U” cell. This cell minimizes walking distance when stand-
ing operators are used. Cells have some natural advantages over the classic assembly
line. First, the ability to use people for more than one activity in a cell allows the control
of demand variations by staffing differently. For example, if a six-person cell were to cut
production by 50 percent, it is commonplace to then staff the cell with only three people
and have each person work two stations. This, of course, requires worker cross-training,
but that is a staple of Lean Manufacturing. Second, cells are much more flexible. For
example, in place of a 20-person assembly line, if we use four- to five-person cells we
have a much greater model-mix capability without creating large batches and without
having large time losses due to changeovers. But the coolest aspect of cells is that,
although it is a very well kept secret, cells can be a natural variation reduction device.
Cells are a very interesting topic, see Chap. 13, Cellular Manufacturing for more details
on cells.

SMED/OTS SMED/OTS stands for Single Minute Exchange of Dies and One Touch
Setups. SMED technology is a science developed by Shigeo Shingo and is designed to
reduce changeover times. The problem is simple. Any machine that has long change-
over times must have an excess capacity to account for the downtime of the changeover.
Furthermore, to supply the rest of the downstream process during the changeover, a
large batch must be stored up. Any effort to reduce the changeover times also reduces
these two forms of waste: excess capitalization and overproduction. (“Single minute”
means a single digit number of minutes that is less than 10.) In actuality, the objective is
to reduce the changeover time as much as possible. In some refined cases, the change-
over is handled by having multiple fixtures on the same basic machine, and by simply
throwing a switch the changeover is made. This is called One Touch Setups (OTS), or