Page 100 - The Toyota Way Fieldbook

Chapter 4. Create Initial Process Stability 77

and on the high end, tubes required 30 minutes to several hours to
complete (some could take days). From this perspective, the low-end
tubes had a narrow range of variation and the high end had a large
range. On a volume basis, 80 percent of all tubes were in the low to
middle range, allowing the variation in time, relative to the total range,
to be isolated within a narrow range.

This narrow range provided an opportunity to effectively align resources
to the workload. The narrow range on the low and middle time tubes
allowed us to establish a takt rate and then to determine the number
of welders needed to meet the rate.
Since the mix of product varies as a result of customer requirements,
it’s necessary to be able to determine the alignment of resources with
the workload on an ongoing basis. The “standard” was determined
based on average volume history, which is a fair indicator, but current
reality rarely matches the average. In this case, current “real-time”
indicators were needed so that everyone could see the actual product
mix at any time and adjust accordingly, in order to maintain flow.

During the creation of lean processes, it’s often necessary to bring for-
ward concepts from subsequent phases and to introduce them “early.”
Utilizing basic concepts of connected flow and pull (to be described in
the next chapter), the team created visual awareness of actual demand
by setting up defined locations and quantities of work in process (WIP)
for each category (low, mid, high). Minimum and maximum quanti-
ties were defined for each location, providing a standardized indica-
tor—brought forward from the standardize phase—for the team so
they could make decisions about allocating resources. These visual
indicators were added throughout the value stream so that each
operator worked to maintain consistent flow.
Defining and controlling the WIP at each operation reduced the range
of throughput time, and decreasing the quantities further will drive down
the overall time. Figure 4-9 plots the results. Clearly, the process is more
consistently achieving a throughput time of 15 days, and the graph indi-
cates that the process is “stable” in terms of this performance. Having
achieved a basic level of stability, this value stream is ready to move for-
ward in the continuous improvement cycle.

Level the Workload to Create a Foundation for
Flow and Standardization

As we saw in the previous case example, the establishment of product groupings
in order to isolate variation is a crucial step in the development of stability and