Labor Content By Process
So to obtain the operator cycle time for the “gather materials” step, we go
by the average lot size in the value stream. Based on information from Figure 1
(averaging the numbers in column 3), the average lot size within the mild steel
value stream is 35 units, so setup times, gather materials, and other activities
performed once per job will be divided by 35. We’ve determined we need 5 minutes to gather enough sheet metal for 35 units. So we divide 5 by 35 and get
0.143 minute, or 8. 57 seconds, as shown as the weighted-average operator cycle
22824 The Fabricator 2:3 Vertical JAN 2016.ai 1 12/14/15 3:22 PM
Shear Grain Form Hardware Laser
The critical numbers in the process boxes are the weighted averages of OCT,
machine cycle time (MCT), and setup time (SUT). That’s because unlike product-specific value streams, our mild steel value stream handles different products,
and the mix might change each day. For gathering materials, the cycle time for
This shows labor content (OCT plus SU T) by process. Note that the forming process is
in danger of exceeding our 115.2-second takt time.
Next we need to know the available time. We have 480 available minutes ( 8
hours) over one shift, not counting 10-minute breaks, which I’ll address later. To
determine takt time, we divide available time (AT) by demand (D): AT/D = Takt
time. We divide 480 by 250 to get a 1.92-minute takt time. Our common unit of
time is seconds, so we multiply this by 60 to get a takt time of 115.2 seconds.
Knowing this, we need to develop a system to produce a unit (component)
every 115.2 seconds—or less than 2 minutes. This value will be used throughout the VSM to determine the appropriate number of people, machines, space,
plant layout, and inventory levels to meet that goal.
Labor content divided by takt time indicates how many people are required
to maintain the required output. To be clear, the labor content of a process may
be well over 115.2 seconds per unit. Labor content and takt time are two different things. If the labor content is less than 115.2 per unit, then we would need
one person to spend at least part of his or her day to accomplish the task. If the
labor content is more than 115.2 seconds per unit, then we would need more
than one person.
Using Post-It notes and a large wall or whiteboard, we show the process in a
flow chart, including all the major variations and percentages of flow—that is,
what percentage of pieces in the value stream share that specific routing path.
As the flow chart in Figure 2 shows, 86 percent of pieces go from raw stock to
the shear and then on to the laser, while 14 percent go from raw stock directly
to the laser.
If you can’t identify a unique flow for all of your products, don’t agonize over
it. Job shops can’t hope to map 100 percent of everything they do. Leave out
the minor product categories. Otherwise you will “what if” yourself into static
For each process we then fill out a form—what we’ll call a process box—that includes the operator cycle times, machine cycle times, setup times, the distance
traveled per unit, and current work-in-process (WIP) inventory (see Figure 3).
Later we will develop a future-state map that reflects the true WIP levels required to maintain output at the takt time.
In practice, you need to account for the true workstation load. For instance,
working from the flow chart in Figure 2, we see that the shear processes only
86 percent of our pieces. Workstations also may process work from other value
streams, which needs to be accounted for as well.
But just to introduce the process box concept, we’ll keep the math simple and
assume that except for hardware, all 250 parts for the day are routed through
every process in the mild steel value stream.
For most processes, we determine the operator cycle time and setup time
with some simple time studies, observing and recording how long it takes operators to perform certain tasks. When an operator retrieves a raw sheet to put
in the laser, though, we run into problems. He’s not processing just one part or
product, but instead an entire sheet that will be cut into a nest of blanks.