Figure 4-2. Processing a Gear

METHOD OF LOAD-SMOOTHING PRODUCTION

Implementation of the load-smoothing system of produc­tion becomes easier when one has a clear notion of what the cycle time is.

We have previously stated that there are 800,000 specifica­tions for Corona. However, in order to make the explanation of the load-smoothing plan simpler, let us assume that Corona has only five types, named А, В, C, D and E.

The required amount (amount of production) and cycle time for the five are given in Figure 4-3.

To obtain the cycle time, the following simplified formula may be used:

„ . , . Daily operating time

Cycle time(tact) = :—j-*—— ° .—-.—rr

Required quantity per day (umt)

Often we see lines making mistakes in obtaining the cycic time. Care must be taken to ensure that this does not happen.

The mistakes occur because these lines calculate everything from the present condition, including equipment capabilities and

	Month	Dav minules, ' 20 work days)	Cycle Time
ACar	4,800 units	240 units	2min.
В Car	2,400units	120 units	4min.
С Car	1,200 units	60 units	8min.
DCar	600 units	30 units	16min.
ECar	600 units	30 units	16min.
	9,600 units	480 units	1 min.

Figure 4-3. Required Quantities and Cycle Times for Five Auto Models

man-hours. They say: "We have this much equipment capability and this many people. Therefore we can produce this many units. And we can produce one unit in this many minutes."

From the perspective of the Toyota system, this approach is totally wrong. "We need this many units today," however, will give the right start. One must obtain the number of people needed to work from the cycle time, which in turn is obtained from the required amount of production for the day. Toyota's aim is to do the work required with the minimum number of people. If one calculates based on what he can do with the people the line already has, then the result is likely to be having too much capacity, creat­ing the waste arising from overproduction.

HOW TO LET THINGS FLOW

Now that the cycle time has been determined, how does it work out in the actual assembly line?

Let us assume that A through E are all assembled by lines e xclusively devoted to each. Thus as seen in the figure below, at Line A, units are moved at a two-minute interval, but at Line E, only one unit is assembled every 16 minutes.

When the separate exclusive lines are merged into one, the How will take the form indicated at the bottom of the figure. At Toyota's assembly line, the cars may be the same Corona, but

Exclusive Lines

саг А c^

С-В && cfig ^

CarC ДШ