Takt time at Toyota do Brasil
With the aim of contributing to the discussion of the importance of takt time, in this short article I will describe how this item is handled at Toyota, as well as briefly present the evolution of takt time at Toyota do Brasil – Indaiatuba plant, as a way of illustrating its use.
Takt time – the heartbeat of the Toyota Production System (TPS). TPS links all production activities to actual customer demand. The language of this link is takt time.
That is how it is at Toyota. The unquestioning observance and the disciplined and complete application of this concept is Toyota’s great differentiator, compared with those who do not observe this small but decisive detail and therefore have difficulty succeeding in the “lean” journey in its essence.
Let us look at an example of an assembly line:
It is very simple and easy to understand when the line is producing a single type of product, but when it produces several types of products it is very common to come across a wrong way of producing or making the products flow.
Let us consider a line that assembles two products, X and Y. The monthly requirement for product X is 500 units and for Y, 1000 units.
Under this condition, one would run product X during the first ten days of the month and product Y during the remaining twenty days of the month. Certainly, proceeding this way, the result of the monthly production on the line will be the same, and on top of that the line supervisor will remark that this is the most efficient way to produce, since it requires only one model changeover –set-up– from product X to Y.
But let us see what must be happening in the preceding process. If products X and Y have dedicated parts to be assembled, the manufacturing process for product X’s part will be extremely busy during the first ten days of the month and idle during the remaining twenty days. And on the production line for product Y’s part, exactly the opposite will be happening. If the assembly line pulls parts this way, the preceding process, so as not to run out of parts, will have more capacity than necessary, hurting the company’s efficiency.
So the question is: what is the most appropriate way to produce the parts?
The important thing is to know that manufacturing any part takes a certain amount of time.
For a part with a monthly demand of 1.000 units, considering that the month has twenty production days, the daily demand would be 50 units; considering a 480-minute workday, the time to manufacture one unit of this part is:
|
that is: it is enough to produce one part every 9,6 min. In other words, these 9,6 min. constitute the time required for manufacturing. Toyota calls this time takt time. Therefore every product, depending on its demand, has a different takt time.
For example, let us consider products X, Y and Z. The daily demand for X is 1.000 units, for Y 500 units and for Z 100 units. The corresponding takt times are:
X |
1.000 units/day; |
480 min. : 1.000 units = 0.48 min |
Y |
500 units/day; |
480 min. : 500 units = 0.96 min. |
Z |
100 units/day; |
480 min. : 100 units = 4.80 min. |
If products X, Y and Z happen to be assembled on a single line, the principle is the same, and it is enough to consider that the dedicated lines for each product are grouped into a single assembly line. The total quantity to be assembled on the line becomes the sum:
1.000 + 500 + 100 = 1.600 units / day |
and the corresponding takt time:
480 min. : 1.600 units = 0,3 min., |
the assembly sequence of X, Y and Z according to demand becomes:
X X Y Z X X Y X X Y X X Y X X Y X X Y Z X X Y ....... |
and, with this assembly sequence, as a result we will have product X every 0,48 min., Y every 0,96 min. and Z every 4,80 min.
In this way, even if the variety of products is large, if the different products are assembled according to each product’s takt time, the various interconnected manufacturing processes will operate in a stable manner, without idleness and without overload, both of equipment and of people.
At Toyota, the most important fact in manufacturing a product, which forms the basis of the production system, is producing according to each product’s takt time.
Below is an example of a real case of takt time and its evolution at Toyota’s Indaiatuba plant, where the Corolla is produced.
Period |
*PTSA |
Takt (min.) |
Shift |
Vehic./day |
08/98 to 05/99 |
10 |
17,7 |
1 |
25 |
06/99 to 10/99 |
5 |
16,7 |
1 |
30 |
11/99 to 02/00 |
4 |
13,0 |
1 |
38 |
03/00 to 06/00 |
4 |
10,5 |
1 |
48 |
07/00 to 04/01 |
10 |
13,0 |
2 |
74 |
05/01 to 12/01 |
8 |
12,0 |
2 |
79 |
01/02 to 04/02 |
4 |
10,5 |
1 |
45 |
05/02 to 08/02 |
4 |
4,9 |
1 |
97 |
09/02 to 01/03 |
5 |
4,5 |
1 |
106 |
02/03 to 07/03 |
7 |
6,0 |
2 |
154 |
08/03 to 04/04 |
9 |
4,5 |
2 |
204 |
05/04 to 12/04 |
8 |
4,3 |
2 |
213 |
01/05 to present |
11 |
4,0 |
2 |
220 |
*PTSA – Period during which Takt remained unchanged.
As can be seen, takt time evolved gradually as demand increased, and it can also be noted that takt time did not change from one day to the next or even from one month to the next. This means stability of the production system, dictated by standardized work. The more constant takt time is, the more stable the production system will be. That is, for every change in takt time, standardized work needs to be redone and updated. To change takt time there must be a consensus across the entire business chain – from the customer who is pulling through demand to the supplier of raw materials and parts/components – because for production it means an increase in labor. Processing this increase, including training new hires, takes at least three months. (It is worth remembering here that labor is one of the factors of instability in the production system and the most complex to control.)
One of the practices at Toyota is to resort to working more hours in the event of increased demand – up to around 30% – keeping takt time unchanged, because, as can be seen in the table above, Toyota operates on two work shifts, with intervals between shifts, which makes it possible to use resources on a special schedule for a set period. (We say a set period because, if the period is long and the demand outlook is promising and not seasonal, the direction to be taken is to change takt time.)
On the other hand, in the event of decreased demand, fewer hours are worked, thus keeping takt time unchanged. Every effort is made to keep the production system as stable as possible, without creating shocks and abrupt variations. The immediate and positive consequences of this “modus operandi” can be seen in the high levels of product quality and of worker safety in carrying out their tasks on the production lines, in addition to keeping the line flexible, capable of meeting demand according to a pull system.
