Wait Time

Waiting is one of the seven wastes first introduced by Taiichi Ohno, and still commonly used in modern Lean.

Wait time is particularly bad because it consumes a non-renewable resource, and an important one at that: Time.

Waiting occurs for a variety of reasons. People often wait for a machine to run, for a delivery, or for someone else to complete a task before the individual can start the next step.

Wait time is not only costly for the labor time that is paid for and not utilized. It also has an opportunity cost to it. Every idle minute means that no product is being produced, that a customer is not being served, that maintenance is not occurring, or perhaps most problematic, that no new ideas are being implemented.

Waiting can be obvious, as when a person is staring at a machine for long periods waiting for it to finish a cycle, or it can be quite subtle, as when a slow computer flashes the hourglass or “spinner” as its CPU crunches the ones and zeros.

Waiting, while difficult to remove at times, has a big advantage in that it takes very little convincing to get a person to buy into the idea that it is bad. Inventory or overproduction, on the other hand, are wastes that people can have some difficulty accepting as problems.

Wait Time and Cycle Time

Wait time is often a component of cycle time. If a process takes 24 minutes to complete, for example, there may be a fair amount of waiting embedded in the operation. Only 18 or 19 of these minutes might be spent doing actual work.

Some people break cycle time into two components: processing time and wait time.

If a process is governed by a takt time, there will be some wait time between the end of a cycle and the beginning of the next takt. For simplicity, I do not recommend including this waiting in the cycle time. I would, however, include the internal waiting in the cycle time. The end of cycle time can be easily captured to increase production (shorter takt), or to rebalance the line. The internal waiting is tied to the process in most cases and is harder to eliminate.

Common Forms of Waiting

• Waiting for a machine to complete a cycle. When a machine is running, a person may be waiting while watching it for errors. Technically, if a person is actively operating the machine, it is not waiting. But frequently, a person will stare at a gauge on an automated machine, observe the machine for problems, or wait on the completion of a cycle because they cannot move on to the next step until the part is completed. In each of these cases, the machine is dictating the schedule of the operator.
• Waiting for parts deliveries. Obviously, people need parts (or files or information) to do their jobs. When the things they need are not available, the person waits. This is challenging to deal with as these waits tend to be intermittent and variable.
• Waiting for a partner. When two people need to do a job together, one often has to wait for the other. The preliminary tasks are seldom perfectly balanced.
• Waiting for support. When there is a problem, operators need to call for help. Even with a sophisticated andon system, there is still a lag between when the signal is sent and when the cavalry arrives. If the signal is sent too late and the person hits a standstill, she waits.
• Waiting out the end of a cycle. When work is not perfectly balanced (and it seldom will be), some operators will have anywhere from a few seconds in a short takt time operation, to several minutes in a longer job. Obviously, the better the line is balanced, the shorter the wait time will be.
• Waiting out buffer time. In addition to the waiting from imbalance, there is frequently waiting as the result of buffer time built into a process. For example, if a process has a problem that delays it for a few minutes every third line shift or so, one approach is to add a few minutes of buffer into the Standard Work. Two out of three times, though, when the extra time is unnecessary, the person will be standing around at the end of the cycle.
• Expected vs. Unplanned Waiting. Some waiting time is expected. Some is not. If an operator is required to wait for a machine to spit out a part, it is expected waiting. If an operator sometimes has to wait for a delayed part to arrive or for an overheated machine to cool down, or for an air tank to fill back up, that is unplanned waiting. Expected waiting can be more easily managed.

Reducing Wait Time

Reducing wait time is a challenge because it is hard for an individual to remove it on his or her own. Machines can be a challenge to automate so a person can walk away while it is running. And even automated machines often require waiting, as a person may have to watch for defects if there is no jidoka (intelligent automation) in use.

Equally challenging is coordination for an individual. Most people have some flexibility in their own jobs but may not have much say in how a support person operates.

And it is even more challenging for an individual frontline employee to arrange for an on call person to answer andon signals. The operator does have some opportunity to reduce defects that drive the buffer time, but actually managing existing variation is normally out of their hands.

For the reasons above, much of the reduction of wait time is done by leaders. They arrange for machine automation, get operators from different areas working together to synchronize work better, and decide how to handle intermittent problems and buffer time.

Resolving intermittent problems is one of the best opportunities available for reducing wait time. You may be able to remove more total time in some situations with aggressive autonomation but doing that takes specialized skills and is resource intensive. Simply eliminating the problems that drive inconsistency into a process will provide more bang for the buck.

In most processes, there is some variation. The longer an organization has been focused on improvement, the smaller the variation will be, but it will still be present to some degree.

There are two basic schools of thought on how to manage it. One way, and by far the most common, is to leave extra time within the process to handle the fluctuation. This means that when there is a problem, the work still gets finished on time. But when things go well, there is a lot of standing around.

Instead, take out the buffers from individual work areas. Rebalance the line at the lower cycles, and free up a person to act as a floater to go where the problems are. The benefit is that the time is consolidated in a way that it can be used. The floater can support the line, but also work on projects without the fragmentation that an operator would have if trying to work on something for a few minutes each cycle.

This wait time reduction strategy does require two main things.

1. Work has to be structured in a way that someone can actually help.
2. Andons have to be installed, and more importantly, answered when there is a problem.

Words of Warning

• Wait time often provides a brief rest for people when the normal pace is fast. If you reduce wait time, be sure that the remaining work is done at a manageable speed.
• Be careful not to become numb to waiting. Slow computers and watching machines operate are both examples of situations where people overlook this form of waste.

Wait time reduction can feel hard because those brief periods of inactivity act as microbreaks. Unfortunately, this creates an internal dilemma for some people. On one hand, they recognize that there is something inherently wrong with getting paid to stand around. On the other hand, they may work exceptionally hard between the waiting periods, and need a quick breather. Or, they may simply not like the prospect of having something taken away from them.

For example, waiting in line at a busy shared copier may give an office administrator a minute or two to chat with coworkers. Resolve that problem, and the social interaction goes away, making the job seem less satisfying for some.

The trick is to make sure that the overall work pace is steady, but manageable. Frontline employees should document the problems, frustrations, and dirty, dumb, and dangerous work. Getting these issues on record and tracking their frequency is a great first step in getting leaders to commit resources to fixing the pace.

As far as other aspects, such as social interaction, there are always alternatives. If working with others is important, a frontline employee should try to get on more improvement teams. They need to think creatively. Finding a win-win alternative to meet a need will keep an employee from hanging onto bad feelings about having something taken away.

Removing wait time is a delicate, emotional process. Taking away waiting, in the absence of other changes, always makes a job seem harder.

Be aware that when you work to reduce waiting time, if you aren’t careful about how you say it, your team will hear that you simply want them to work harder, or worse yet, that you don’t think they are working hard enough.

Make sure that you focus on taking away frustrations instead of just talking about getting rid of the waiting. Looking at the big picture and having a bona fide concern for the challenges team members face in their job will go a long way to making people be more accommodating of the drive to reduce waiting time.

Key Points

• Wait time occurs whenever a person is inactive while he or she could be doing productive work.
• Reducing wait time can have a negative emotional effect on team members. This is especially true if they work at a fast pace when they are not waiting.

Do not focus specifically on reducing wait time. Instead, take a holistic approach to waste. Look for all the wastes that affect a process and create a new operation that minimizes all the different forms of waste.

A good place to start is to train a team on how to use the waste recording form, and then ask each operator to post one in their work area to start tracking the things that reduce productivity.