Keep Calm and Stop the Line—Part 2

In manufacturing, a common sentiment is that the line (or generally the process) must run. There is some truth to that, but—counterintuitively—for a system to run well you need to know when to stop it too. This is my second post in a series giving you an overview on when it may be better to stop the line rather than keeping it running (and making everything worse). Keep on reading!

Stop the Line for Problems (That You Can’t Resolve within the Cycle)!

Broken Machine in JidokaThe next reason to stop the line is in the case of problems. These can be any kind of problem that cannot be resolved within the cycle. For example, there may be quality problems. The GM example in the previous post describes this, and how it caused lots of problem for processes downstream. If they installed the wrong engine due to a mismatched delivery, many subsequent processes working on the engine had also problems, greatly compounding the quality problems stemming from one issue.

At the end of the line, many more people were needed to resolve these issues and fix the car. Similarly, in some European plants in the 1970s and 1980s, they had as many people fixing cars as they had building them in the first place.

The need to stop the line applies not only to quality problems, but also to other types of problems like missing material or a broken tool. Similar to quality issues, problems will compound. If you simply skip installing the missing material, other stations may have problems later on, and you need to track what is missing and fix it. Similarly, if your tool or machine is broken, continuing with a flawed or missing work step will cause problems downstream.

Hence, your operators need to stop the line if there are problems that they cannot resolve within the cycle. This is even the justification for the well-known Toyota approach of Jidoka, or autonomation. Jidoka means a process stops automatically if there are any irregularities.

One Station Andon CordYet, you want to stop the line as little as possible. For this there is the andon line pulled by the operator in case of problem. This pull gives signal to an andon board, which then calls help.

The key here is to provide help to the operator quickly. If the operator has to fill out a maintenance request so that maintenance shows up two hours later, then your line stops for at least two hours, which is a bit much. Toyota has a team structure where an experienced team leader is right there, with the focus of supporting the operator and enabling him to do his work. A team leader is in charge of only four to five operators, allowing fast response times. In my experience, such a team leader can resolve most smaller problems within the cycle, and the line doesn’t even have to stop.

Stop the Line to Put the Focus on the Problem!

Toyota also does not like a stopped line. But  stopping the line prevents much larger issues and expenses downstream. At the same time, it puts a lot of pressure and focus on the problem, regardless if it is quality, lack of material, broken tools, or something else. If the line stops, the entire line has an interest to resolve the issue. Initially it is only the team leader assigned to that station that helps. But if there is a longer stop, soon other team leaders or even the group leader joins to help with the problem.

For even longer stops, successively the line manager, then the section manager, and after that the plant manager will get an automatic message alerting them to the problem. This puts a lot of focus on the problem, as well as a lot of pressure to fix it and to prevent its reoccurrence. A stopped line is pain. But just like in your body, pain is good as it alerts you (e.g., a toothache alerts you to a broken or infected tooth). If you keep the line running, you will not feel the pain as much, just like taking some aspirin will reduce the pain from your toothache. But this does not solve the problem but only addresses the symptoms, and sometimes not even well. Meanwhile, the tooth will get worse, just like your production system will.

Hence, stopping the line for a problem will increase the pressure for the problem to be fixed (and NOT for the line to run anyway!). Please note that this pressure is also not so much pressure on the operators, but rather pressure on the managers to improve the system. The operators can and must help, but the responsibility lies with management.

Hence, stopping the line will put the focus on the problem very much! This is a great driver for continuous improvement (kaizen), and a plant manager who is alerted to a line stop for the same reason multiple times automatically will prioritize this problem.

Stop the Line If There Is a Safety Risk!

Safety gearAnother reason to stop the line is if there is a safety risk. The health and safety of your operators should be paramount to your production output, and a health risk (both short-term accident and long-term hazards) must stop the line. Please don’t do it like GM Fremont and run your machinery while people are injured and bleeding underneath.

I had one such example in one of my plants, where at one point the monthly blood test for our welders came back with elevated levels of metals in their blood. As soon as this was known, the welding in the plant stopped. The permitted levels were very much on the safe side, and the health of the welders was not (yet) in danger. But we did not want to wait until it was a health risk, since we took care of our operators (and the government would have punished us hard if we didn’t—rightfully so).

Of course, our plant needed the welded parts. Not having them was a major pain. But this pain was good, because it motivated management to act fast. Three days later we had improved venting hoods sucking up the welding fumes, and production continued.

Hence, stop the line if there is a health or safety risk for your worker. At Toyota and also many other plants, safety is the first thing discussed at any team meeting and is the first KPI looked at.

Stop the Line to Increase Flexibility!

Ice Cream Change Over Wheel 10 FlavorsYou need to stop the line to improve flexibility. By this I mean changeovers. Large lot sizes may allow you to run the line more since you are losing less time for changeovers. However, whenever possible go for smaller lot sizes rather than longer production, because large lot sizes are nothing other than overproduction. You don’t need the items (yet), but you make them anyway.

Hence, it is better to stop the line more often for a changeover rather than having large lot sizes. The whole idea of reducing changeover times (i.e., Single Minute Exchange of die, or SMED) is NOT to produce more, but to have smaller lot sizes. My blog has a lot of articles and series on SMED and changeover sequencing.

Stop the Line for Maintenance!

Oiling MachineFinally (and hopefully obviously), you need to stop the line for maintenance. Only a properly maintained machine can run well. Otherwise, you will have quality defects and also unplanned stops. If you stop doing maintenance on your car, eventually something will break and you will lose a whole lot of time being stranded on the road. While maintenance also takes time, it can be planned, whereas an unexpected breakdown hits you right when you need the machine. While some maintenance can be done on a running machine, a whole lot of other maintenance activities need the machine to be stopped.

Hence, it is necessary to stop the line for maintenance. There is a whole framework around the idea of maintenance, Total Productive Maintenance (or TPM). I have written a whole series on Maintenance and TPM with much more detail.


Overall, there are quite a lot of valid reasons to stop the line so in turn the line can run well. If you don’t stop the line, the line will stop itself—more often and more dangerously than if you stop it yourself. Or, rather, have your people stop the line. Many of the reasons for stopping the line may pop up on short notice, and it is only the worker on the line who can react fast enough to prevent the issue from becoming worse. You need to empower your people to stop the line (e.g., using an andon line) and also train them to actually stop the line AND provide timely support. I have seen quite a few lines having a fancy andon system but the workers never pulled the line, either because then they had problems with management or they learned that nobody will come to help, or both.

Let me know in the comments if you have another point or idea for when to stop the line. Now, go out, stop the line to make it run, and organize your industry!


1 thought on “Keep Calm and Stop the Line—Part 2”

  1. I do car repair work on the side, and I can safely say that most automotive breakdowns will show signs and symptoms for day or weeks before something breaks completely.

    Another thing I can safely say is that taking the downtime and the cost of addressing problems early on is a hell of a lot cheaper than running and gunning the machinery until something fails completely and often make the repair an order of magnitude more expensive.

    Quite a few Honda 2.4L earth dreams engines have timing chain issues when the tensioner starts to go bad and there’s slack in the chain. As that happens, the engine will make ugly noises on startup that mostly go away when it warms up. When they show up, it’s usually around 100k miles (160,000km for the folks outside the US). If caught early enough, it’s a relatively easy fix because the front cover on the engine has a small hatch to access and remove the tensioner. But if someone ignores the issue, eventually the chain will slack up enough to start skipping gear teeth and eventually the pistons will collide with the valves due to cams and the crankshaft turning out of sync. When that happens, the most practical solution is an engine transplant with a used good motor.

    A lot of the times when this issue shows up, you’ll get error codes related to the high pressure fuel pump performance. The pump is fine, but it’s not developing the correct pressure because it runs directly off of the camshaft that’s no longer turning in sync with the crank and the pistons, throwing off the fuel injection and ignition works.

    I’ve also seen the same scenario play out repeatedly at my previous job whenever there’s a production crunch during the busy season. The line would run six days a week along with at least two hours overtime Monday through Friday. No maintenance getting done apart from quick fixes and, any halfway major work would be put off til Sunday or Saturday (if the main line isn’t running on Saturday).

    This would usually go on about two to four weeks with few major problems. After that, it’s at least one major breakdown every week where the line would stop for an hour or longer while the supervisors ran out visibly panicked. Fun times.

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