MTFB and Maintenance cost excel

Calculation for Mean Time Between Failures (MTBF) Transcript

I'd like to take a few minutes and go through the calculations for mean time between failure and the PM versus breakdown. This information is also in your textbook if you need to look at that. But let's go through an example real quick of how to calculate mean time between failure.

In this case, you're going to have your data given. In this case, you're going to have the number of failures as two. Then you're going to have the number of units tested. It's going to be 20 in this example. You're going to run your test over a thousand hours. And at 200 hours, one system is going to fail. And another system is going to fail at 600 hours. So you've got two failures over your thousand hours. To calculate your percentage of failures, you want to take the number of failures and divide by the number of units tested. So it's pretty straightforward and that's going to give you 10% in this example.

Next step is you want to take a look at the number of failures per operating hours. So your total operating time is going to be the test time, times the number of units tested. And that's going to give you 20,000 hours, the non-operating time. It's going to be the test time minus the point that System 1 fails, plus the test time minus the point that System 2 fails. And then to get your number of failures you're in, you're going to take the number of failures, which is 2 divided by the total time minus the non-operating time. And that's going to give you your N.

Then to calculate your mean time between failures, you're just going to take your N. And you're going to divide that, you're going to divide 1 by the N itself. And that's going to give you a mean time between failures of 9,400 hours. So that's pretty straightforward. For the breakdown operation, breakdown versus preventive maintenance, let's take this example here where we have an observation time of 12 months. If you have a breakdown, it's going to cost the company about $400 in loss productivity. If you hire a preventive maintenance company, it's going to be, it's going to cost you $200 a month. But with that, the preventive maintenance company is saying you can still expect about one breakdown per month. And again, this data will all be given to you or you'll be able to collect this data in the situation.

And then you're going to look at the number of breakdowns per month. So zero breakdowns, you had two machines that did not. In Month 2, you had six. And number of breakdowns two, you had four breakdowns that occurred. So your first step then, you're taking the, again, this data is given. So the first step is to calculate your frequency. So your frequencies for zero breakdowns, you're taking the observation time or actually you're taking the number of months that break down occurred in this case. Two divided by the observation time, which is going to give you 0.167 and you'll do the same for the next. You'll take the, you take the, the six, which the number of breakdowns are the number of months in breakdown divided by the total month. And you do the same thing for the next field.

And then to get your overall calculation, you have to take the number of breakdowns and multiply those by the frequency and then add each of those together. So in this case, we're going to take the 0 times 0.167 and then we're going to add that to 1 times 0.5 and then add that to 2 times 0.333. And that's going to give you an average breakdown of 1.16 per month.

So from there, it's pretty straightforward. To get your expected breakdown cost, you take your total breakdown cost and you multiply that by the breakdowns, expected breakdowns per month. And to get the preventive maintenance costs, it's much easier. You just need to take the preventive maintenance costs, multiply by the number of breakdowns and then add your breakdown cost.

So I hope this will help you as you work through the problem, but make sure that you go through the book also and look at those examples.

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