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.
Let’s talk about how this works in real life. Do you remember the clip of the old “I Love Lucy” show—the one where she is working on the chocolate line?
In the episode, you can see in an amusing way, how cycle time and takt time interact. Lucy and Ethel are working in a chocolate factory, and have to wrap chocolates moving along a conveyor in front of them. Initially, the pace is rather slow. Presumably, the conveyor is running at the speed that matches takt time—it is set so that a chocolate passes Lucy every three seconds.
If she was working alone, she’d have to be able to wrap each piece within three seconds to keep up. Since Ethel was with her, she only has to do every other piece, so she’s got six seconds. If it takes her three seconds, she’s got a three second cycle time (or processing time), and three seconds of wait time.
To get a few laughs, eventually the line speeds up. In reality, this happens when customer demand rises. At some point, Lucy realizes that she can’t keep up, and chocolate starts flying. In your workplace, the effect is more subtle, but the same thing happens. When the pace is faster than the cycle time, workers can’t keep up with demand.
On the flip side, if the cycle time is much lower than takt time, the operator will be standing around. Not a very efficient situation. The goal is to balance cycle time to takt time.
 Productivity can be measured many ways. One of the most common is ‘units per labor hour.’
 There’s some math involved here that depends on the spacing between the chocolates to get the right speed of the conveyor.
 Sorry. More math here…To figure out how many people you need for a production task, you divide the total cycle time of all tasks by the takt time. It doesn’t matter whether people do tasks in sequence (like on a true assembly line) or they all do a complete unit, like the Lucy example. The only catch is that math assumes that the work is perfectly balanced (everyone gets the exact same amount of work). It never is, so there always more people than the equation says there should be.
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. Make sure you observe the operator before you to jump to conclusions. In all likelihood, the person is slower because he is not following the process, not because he can’t do the work. In most cases, this is a training problem, meaning the operator doesn’t know the right way. That’s not the operator’s fault. It’s yours.
One of the more As a leader, you will have to blow the dust off your old textbooks and brush up on your math to be really good at Lean—especially as you advance towards more sophisticated concepts. If you don’t have these skills, get them. Your job will be much harder than it needs to be if you lack the ability to solve increasingly difficult math problems.
© 2009-2014 by Velaction Continuous Improvement, LLC. All rights reserved.
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