There was an interesting search in my logs today.
[does a system have a single takt time or multiple]
I always figure that if one person is looking, others are also curious, so let’s address it and maybe there will be a better search result for the next Googlenaut out there.
Takt time is local.
It is calculated based on the demand from your customer.
This is a critically important concept because for takt time to be of any use, it has to be relevant to the people who are actually doing the work.
A factory has four final assembly lines that feed into shipping.
There are 420 minutes of working time in the day, and total aggregated leveled output is 350 units of production.
What is the takt time?
For shipping, it is straight forward. The customer takt time is:
420 minutes / 350 units shipped = 72 seconds
So for shipping to stay on task, their process must be capable of packing and loading one unit every 72 seconds. If they can’t consistently achieve that, they are falling behind.
What about the assembly lines?
You don’t know, because you don’t know what each of them is expected to produce. You could say that the factory takt is 72 seconds, but that does not pass the “so what?” test for the people working on those lines. But if you know that:
Line A’s leveled production is 75 units
Line B’s leveled production is 50 units
Line C’s leveled production is 100 units
Line D’s leveled production is 125 units
then you can determine a meaningful takt time for each of those lines.
Line A: 336 seconds
Line B: 504 seconds
Line C: 252 seconds
Lind D: 201 seconds
In reality, I am going to run these lines a little faster, but that is a different topic entirely.
Now we have a takt time that actually matters. It reflects the work cycle that must be achieved for that line to meet its obligation to its customers.
Upstream there are fabrication or other feeder processes. We have not yet gotten them into directly linked flow.
Process E feeds one part to each unit produced on Line B; and one part on every FIFTH unit on Line C. What is the takt time?
Line B needs 50 parts. Line C needs (100 / 5 =) 20 parts for a total of 70 units of output.
So Process I has a takt time of (420 minutes / 70 units of output =) 360 seconds.
Value stream mapping is very useful for untangling this. Hopefully you can also start to see one of the reasons we work so hard to level volume and mix.
This isn’t complex stuff, but on the other hand, if you oversimplify it then it becomes meaningless. Remember, this is not about OUTPUT, it is about testing whether your process has succeeded each and every time it is carried out. You can only do that if you know what is expected right then and there.
Go to your shop floor. Watch the work. Can you tell, with each unit of output, whether the team member was successful that time? (More precisely, can you tell whether you were successful in giving that team member what she needed to succeed!). If you can’t tell, I guarantee that the people doing the work have no idea, which means you are leaving them to guess. Not a good thing.