with the production kanban, and creates the next 10 minutes worth of
production. This paces the one-piece flow assembly line.^5
When this heijunka process is applied throughout the plant (using the
visual management boards known as heijunka posts), it’s possible to
see the state of the whole process for a whole day in one place. It is
natural within the Toyota philosophy to use the material handler—or
“water spider,” as they are sometimes called—in this capacity, since
they can see the entire material and information flow in their route.
By creating this leveled condition throughout the plant, all forms of
work can be standardized based on the 10-minute interval. This sim-
plifies each operation, and it becomes immediately apparent at a
glance if the standard is being followed. Once this condition is met,
highly capable individuals who can carefully observe, understand, and
think can understand the condition of the entire plant.
The heijunka post levels production across many part numbers. To
achieve this, changeovers (fixture changes on the assembly line) were
reduced to less than the takt time (takt time equals available work time
divided by customer demand). A two-shift assembly line is changed
from 90 to 125 times per day. The takt level is achieved through
conveyor line spacing and the rebalancing of work elements for the
team of associates on the assembly line. Internally there is a two-way
kanban to an intermediate parts store (withdrawal) and then to a
manufacturing process (production) for the parts pulled for use by the
final assembly area. Kanban are brought to the store 88 times per day.
Achieving these kinds of pickup and delivery frequencies requires a
fine-tuned process that is highly stable. Even small problems will disrupt
production and show up almost immediately. For this reason, for a
company to be successful with these interruptions it must be committed
to fixing problems immediately and then following up with permanent
countermeasures. In terms of the continuous improvement spiral in
Figure 3-4 (Chapter 3), the plant is several iterations down the spiral of
stability, flow, standardization, and advanced production leveling.
Performance results on the model lines have been impressive. Product
cost has been greatly reduced, while quality and delivery have risen to
noteworthy levels. Most important, DMMI can utilize the success of
this activity on other existing assembly lines. DMMI team associates
have been directly involved and are transitioning to a new level of
“kaizen mind.” This allows the company to foster a new culture where
associates’ kaizen power can be tapped and implemented quickly.Chapter 19. Lean Implementation Strategies and Tactics 423(^5) In fact, the process is similar to that shown in Figure 19-5, though the assembly is a true one-piece
flow, and there are no FIFO lanes in the process.