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Takt Time vs Manual Cycle Time: The method to calculate the Quantity of Operators.

This article was written based on my experience as consultant. After many Kaizen event I have found there is 2 misunderstandings about how calculate the Number of Operators that are needed to run a production line or manufacturing cell.

When you implement standardized work a Takt Time base on customer demand must first be established for the area in question, for example 30 seconds TT, this is equal to set a rate of 120 UPH (Units per Hour). Therefore; the next question is how many workers are needed in the manufacturing area, at this rate? The answer depends on the total work content in the area and relation to demand ( TT). It's also known as graph of “Takt Time vs Manual Cycle Time”, in many industries.
The more work content, the greater the number of workers that will be required; the less overall work content, the fewer workers that are needed.
Misunderstanding 1:
I have found there is a misunderstanding of Overall Work Content, many people take the Cycle Time complete (Machine + Manual) and that is not ok, they must use the “Manual” Overall Work Content (Total Manual Cycle Time)
Please see this example.

The calculation shows that is possible to run this Manufacturing Cell with just 3 operators. 

Misunderstanding 2:  
There is other misunderstanding this is about the representation of TT, many people don’t understand this concept how interpret and calculate the Quantity of operators when they have operators working in parallel.
For example; when there are operations that are not possible to be separated, the activity must be done from the start to the end by one operator at time; and if the cycle time is greater than Takt Time; then you need use more than one operator to cover the rate needed, this means to have two or more operators working in parallel, for this case the Takt Time must be different.
You should never use the average of those operators as the Manual Work Content, you need represent as it is and make the calculations using other Takt Times equivalent.
Please see this example.

The calculation shows that is possible to run this Manufacturing Cell with just 5 operators; please note that here there is two Takt Times, but don't get confuse at the end the Cell will run at 30 Seconds of Takt Time; equivalent to 120 UPH. The operators 1 and 2 must works at 3 process in sequence  (Press, Trim and Spring).

I hope this be useful for you in your next Kaizen event.

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