Another interesting “homework problem” showed up in the searches today:
an assembly line turns out parts at the rate of 250 per hour. on the average, the line must be shut down for maintenance for 20 hours during a month. how much production is lost each month?
Wait a minute!! What about the 20 hours * 250 units / hour = 5000 units? Isn’t that lost production? Maybe. What problem are you trying to solve?
I’m making a couple of assumptions here. First is around the word “maintenance” vs. the word “repair.” If the line requires 20 hours of maintenance to run reliably and avoid repairs, then this time must be planned into the expected monthly production. Thus, no planned production is lost.
If no production above the planned level is required, then I can’t say any is lost. This is why one-dimensional questions like this are so dangerous. Whenever we are confronted with questions like this, we must always ask another:
Compared to what?
What should be happening? What is normal? What is needed? Simply saying that the line (when it is running) can produce 250 units per hour is data, but it gives us nothing to act on.
Here is the rule I have been pushing lately:
Whenever you measure something, there are always two values.
- What you measured.
- What is required or expected if the process or thing you are measuring is problem free or otherwise doing what it should or what you expect.
This is equally true for an observation.
- What you saw.
- What you should have seen if things were as expected or problem-free.
Then you can start the process of meaningful inquiry.
If my line produces 250 units / hour when running problem-free, and requires 20 hours of maintenance a month to be able to do that, we have a single piece of information: How much production I should expect during the month.
Is that enough? Then no problem, turn your attention to something more pressing.
Is that not enough? OK – now we have to get serious.
A lot of management teams confronted with this problem are going to reflex to just allocating fewer hours to maintenance in order to get more hours for production.
Don’t do it.
Just cutting maintenance time is going to make things worse. Maybe not this month or even next, but sooner or later you will be losing a lot more than 5000 units of production / month. What will make this frustrating is you won’t lose them all at once. You will experience slowdowns, short stoppages, jams, and all of these things will seem like a normal day – only you won’t be making 250 units per hour anymore.
This is where a lot of management team struggle. They only look at “maintenance hours” and issue a directive to cut those hours.
But “maintenance hours” is a metric that you cannot action directly. This is a classic example of what I wrote about a couple of years ago in “Performance is the Shadow of Process.”
Worse, this is a step away from what you are trying to accomplish… which is what?
Key Question: What Problem Are You Actually Trying to Solve?
“I need to reduce the time we spend on maintenance.” is not a problem. It might be a desire, or a possible solution, but if you start here, you are already restricting your thinking.
If you did reduce the time you spent on maintenance, what would you be able to do that you can’t do today? Why is this important to work on?
(Sometimes I get “We wouldn’t spend so much time on maintenance.” I always have to laugh when I hear something like this. Aren’t circular arguments fun? “OK, why is it important to spend less time on maintenance?”)
After some discussion, we might arrive at something like a need to produce another 1000 units / month to meet increased sales demand.
That becomes our challenge. Then the fact that we spend 20 hours / month doing maintenance is part of (and only part of) the current condition. But I can ask other question now such as:
How fast must we produce (units / hour) to get another 1000 units / month? You would be surprised how often the math tells us a number that is slower than “250 units per hour.” Huh. So maybe that’s the rate when things are running smoothly… where is the time going?
The point is that it is critically important to understand why you are asking how much time is being “lost” to maintenance to avoid jumping to a solution.