In nearly all continuous improvement projects, it is important to know how long work takes to accomplish, or the cycle time of the process. So, what is cycle time?
Lean defines cycle time as the time it takes to do a process. It includes the time from when an operator starts a process until the work is ready to be passed on. This cycle time definition is rather simplistic, though, as there are several elements that can cloud the issue. Batching makes it hard to determine cycle time, as does waiting. On linked assembly lines, there is often waiting at the end of a line shift. That waiting is typically not considered part of the cycle time, but waiting within the work is generally included. Put simply, cycle time is the minimum time a stopwatch would have to run to produce a good unit of work.
The purpose of knowing cycle time is to establish staffing, do demand planning, and provide the basis for continuous improvement.
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Lean, and all continuous improvement philosophies, place a tremendous emphasis on time. After all, it is a component of one of the key operational metrics that many companies use to determine performance—productivity.
Many people define cycle time in slightly different ways. One definition you might hear is that cycle time is the time between the completion of one unit, and the completion of the next unit. There is a problem with that definition of cycle time, though. Sometimes an operator finishes her work early, and has to wait to start the next one.
In practice, that definition means that cycle time will always equal the time between shifts of an assembly line (most likely set equal to the takt time). Plus, all the cycle times would be identical on that line. Those who use this definition, though, often break it into two smaller components—processing time (the time an operator is actually working) and wait time. So, under this definition, cycle time looks like this:
Cycle time = processing time + wait time
The more common definition of cycle time is the equivalent of processing time in the equation above—the start-to-finish time of an individual unit. Note that even this definition of cycle time creates some opportunity for confusion. Often there are bits of waiting within the process. Perhaps a person has to wait 20 seconds for some glue to dry or for 16 seconds while a machine tests a circuit. Most people differentiate between the waiting embedded within a process and the waiting to pass the work on once the work is complete. Ironically, that end of cycle waiting is more prevalent in Lean organizations where operators can’t pass work on until there is a pull signal.
We recommend using the elapsed start to finish time for cycle time. This would include the waiting within the process, but not at the end. The truth, though, is that as long as you understand the concepts, the choice you make as to definition is less important than the fact that measuring processes and understanding the time content tends to lead to improvements. Just makes sure you know the usage at your company to prevent misunderstandings.
Visit part 2 to continue reading about cycle time.
 Productivity can be measured many ways. One of the most common is ‘units per labor hour.’
It takes a long time to get past the idea that cycle time is not a measure of you, but rather of your process. Most people see a stopwatch and immediately get nervous or annoyed that they are being evaluated. The best way to get past this hang-up is to get used to being measured. Volunteer to be the one to get timed for Standard Work as often as you can.
You will also have to get used to the idea that no cycle time is ever low enough. Just when you think you’ve finally settled on how long a task should take, one of two things will happen. First, someone will have an idea, and they will put it in place, lowering the cycle time. This is more of a mental block than a real problem. If a process takes seven minutes, and someone comes up with a good way to do it in three, what’s the problem? The problem is that those four minutes get filled, so it feels like more work is getting dumped on you. Step back, though, and look at the quantity of time, not the number of tasks. The catch—if more work is added before the cycle times come down, you are doing more work.
The second thing that might happen is that your boss gives you an improvement target. This often happens when she knows demand is picking up, and has a new target takt time to hit. That will result in a push to improve a process and reduce the cycle time. Until you get comfortable with the continuous improvement process, you will struggle with this. But think of it like visiting a new city. If you know the general rules of travel—how to get through an airport, read a map, and rent a car—you’ll be able to have some fun. You wouldn’t avoid travel because you don’t know the exact layout at your destination’s airport. In the same way, once you get a few improvement successes under your belt, the goal of reducing cycle time won’t feel like such a burden.
If cycle times vary widely, whether from cycle to cycle, or from person to person, it is an indication that there is something wrong with the process. On occasion, you will have one person who can’t seem to keep up.
© 2009-2014 by Velaction Continuous Improvement, LLC. All rights reserved.
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