Interesting Question about Cycle Time

An interesting search landed someone on the site recently. Here it is:

a machine is producing 55 parts in one hour. what is the cycle time for each part.

Likely this is someone Googling his homework question, but I’d like to take apart the question and discuss it. If this is a homework question, I would contend that the likely “correct” answer is wrong.

Take a pause and think about it for a second. How would you reflexively answer this question?

 

 

Someone encountering this question is likely to simply divide the 55 parts of output into the 60 minutes of elapsed time. Doing that, we get something just over 65 seconds per part.

Which is interesting, but it isn’t the cycle time per part. It is the average rate of production, but it isn’t the cycle time.

I contend you don’t have enough information to answer the question. To really do that, you need to get your safety glasses and hearing protection, go down to the machine with a stopwatch (I’d suggest one with a lap function) and click off the elapsed time interval between each and every part as it come off the machine.

Why?

Well… let’s say that the machine is actually running at a cycle of 55 seconds / part when it is actually operating, but there are frequent jam-ups that the operator has to clear.

Isn’t that a completely different story than running smoothly with one part coming off every 65.45 seconds?

Think about it.

7 thoughts on “Interesting Question about Cycle Time

    1. Hi Mark –
      Yes – you can only see those issues by actually measuring cycle time vs. trying to calculate it.

      I wonder, though, how many people seeing that question would simply reflex to calculating 65.45 seconds, and answering it without thinking about what information they DON’T have.

    1. Scott –
      If the system were running at a pitch of 60 minutes, that is using 60 minute blocks of time to normalize production rates across a variety of items, then yes – that would be legitimate. I honed in on the “cycle time for each part” bit of the question in this case.

      As you can see, these “test questions” aren’t quite as straight forward as they seem, are they? 🙂

  1. So could the premise be that the machine actually produces a part every 50 seconds for a run rate of 72 parts/hour if the machine was running smoothly? However if you don’t actually go to the floor and observe the operations how would you know that? Great post!

  2. I agree that there is insufficient information. Like Scott wrote, the cycle time might be 60min, but also in continuous operation. That might be the typical case for a pipelined production.

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