Log in | Register | Contact Us | View Cart


No comments

Cycle Time (+ 9-Page Lean PDF +Videos +MP3 +Form )

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?

Time Observation Sheet

Track your cycle times with our free time observation sheet (Click image to get it.)

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.

Click this cover image to download this term on PDF.

In addition to the vanilla version of ‘cycle time’, you may hear several other variations which lead to further confusion: operator cycle times, machine cycle times, or automatic machine times.

The purpose of knowing cycle time is to establish staffing, do demand planning, and provide the basis for continuous improvement.

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.[1]

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.

Real(ish) World Cycle Time

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.[2]

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.[3] 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…

[1] Productivity can be measured many ways. One of the most common is ‘units per labor hour.’

[2] There’s some math involved here that depends on the spacing between the chocolates to get the right speed of the conveyor.

[3] 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.

View additional continuous improvement information

  • Using the wrong term creates confusion. You say one thing, and others hear something else. Make sure you know the accepted definitions of these terms in your company. Regardless of the definition that you use, make sure you understand how people and machines interact, and how their current processes stack up against the takt time.
  • This entry focuses on the time it takes a person to do a job. Many times, a worker will be using a machine. Make sure you understand how operator cycle time relates to machine time (also called machine cycle time), or to automatic machine cycle time. A Standard Work Combination Sheet (SWCS) shows this interaction.
  • Cycle time should be measured for a process, not a person. Obviously, a fast person will post better times than a slow one or an untrained one. Solid, repeatable processes and good training, though, will minimize this variation. Regardless, time an average person at a normal pace when measuring cycle time. It will cut down on the number of disputes about whether the time is reasonable.
  • Takt time remains constant unit to unit. If cycle time was measured on each cycle, there would be some variation. The more variation, the less stable the process is, and the more wasteful it is. Get rid of variation, and average cycle time will come down.
  • Before attempting line balancing, focus on cycle time reduction. Bring the cycle time down so you don’t just move a poor process from one location to another.
  • Never trust an even number for a cycle time on a Standard Work Combination Sheet. There is only a 1 in 60 chance that a time ends in :00. (There is only a 1 in 15 chance that it ends at any of the four favorite SWAGs—:00, :15, :30, or :45) It indicates that whoever recorded the times logged estimates. That means that nobody observed the work when recording the SWCS, which means that there is probably a lot of waste in the process.
  • Standard Work Sheets document cycle times. Periodically review the sheet to make sure that…

View additional continuous improvement information

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…

View additional continuous improvement information

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. 

As a leader, you will have to blow the dust off your old textbooks and brush up on your math to…

View additional continuous improvement information

  • Cycle time is the length of time—start to finish—to complete a process. It should include the waiting steps that are part of the process.
  • Some definitions of cycle time vary—make sure that you use the term the same way your company does.
  • Cycle time should be balanced to takt time to create an efficient workspace that can meet customer demand.
  • Strong math skills are needed to progress in Lean.

Leave a Reply

You must be logged in to post a comment.

Copyright © 2009-2018, Velaction Continuous Improvement, LLC | Legal Information | Disclaimer