Cycle Time

What is cycle time? Lean defines cycle time as the time it takes to do a process (we’ll get to more detail on the definition of cycle time later). In addition to ‘cycle time’, you may hear several other variations of the term: operator cycle times, machine cycle times, or automatic machine times.

Lean, and all continuous improvement philosophies, place a tremendous emphasis on time. After all, it is a component to one of the key operational metrics that many companies use to determine performance—productivity. (Productivity can be measured many ways. One of the most common is ‘units per labor hour.)

Many people define cycle time in slightly different ways. Cycle time is one of them. 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. What’s the problem with that? Well, 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. As long as you understand the concepts, don’t worry too much about which definition is right. 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—its speed is set so that a chocolate passes Lucy every three seconds. (There’s some math involved here that depends on the spacing between the chocolates to get the right speed of the conveyor.)

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. 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.

So,if it takes Lucy 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.

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.
• 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 cycle time will come down.
• Before attempting line balancing, work on cycle time reduction—bring the cycle time down. It will prevent you from moving 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 the times that are recorded match reality. If they don’t there is a high likelihood that the process is out of date, raising the chance of quality problems.
• Cycle time gets confusing when batching is involved. Lean tries to get rid of batching, but it still occurs. To find the cycle time of an individual part, you end up doing what is called amortizing, or allocating the time that is done for all the parts at once. For example, the setup time of a machine is divided up between all the parts in that run. Or, in an assembly area, a person might apply glue to several parts and then shine an infrared light on several at once to set the glue. The best way to handle this problem? Try to get rid of batching!

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 will happen is that your boss will give you an improvement target. She knows demand is picking up, so she 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.

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.

• Cycle time is the length of time—start to finish—to complete a 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.

Try timing your processes. For the shop floor, use the Time Observation Sheet. In the office, use the Office Process Recording Sheet. You will likely learn a great deal about your operation simply by watching and timing. If your cycle times are significantly different from each other, you should start your improvement process by focusing on variation reduction.

If you need help improving your processes, contact us at Info@Velaction.com. We offer a wide range of Lean training and consulting services to help you accelerate your improvement progress.

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