The most important thing in KPI maintenance is to reduce downtime of critical tools.
And even more important is to reduce unplanned downtime.
1. MTBF – Mean time between failures
Short description: the average amount of time between 2 consecutive failures
Who uses it (importance): higher management (Med), factory management (High), unit management (High)
Description: This KPI lets us see how long has passed on average between consecutive failures. We are looking for problematic tools (first chart) and then we will look to see if this is a recurring problem (second chart).
In the following example we can see that tool 29 has a failure every 9 hours and tool 27 can go more than 2 weeks without a failure. We can easily find the problematic tools and check them. On the second chart we look at tool 19:
By looking at tool 19 (the following chart) we can see that the tool used to be on the 20 hours MTBF and failed every 12 hours in the last 3 months, so we will need to investigate that tool to help it return to the 20 hours’ or higher point.
2 ways to calculate MTBF:
- Accurate:
- Time from last failure = date (+time) of beginning of failure less the beginning of the previous failure.
- Do an average on the above.
- If there is no failure in the time period, take the end time of the time period (if it is a monthly period, take the last day of the month) and subtract the previous failure date.
- Easy way: MTBF = Time period / Number of failures. For example, if we have 3 failures in a 720 hours month, then MTBF = 720 / 3 = 240
2. MTTR – Mean time to repair
Short description: the average amount of time to repair a failure
Who uses it (importance): higher management (Med), factory management (High), unit management (High)
Description: how long it takes on average to repair a tool once a failure occurs.
If we look at a specific tool (tool 19), we see that it used to be fixed in an hour, but for some reason takes more than 2 hours to be fixed now.
The story that MTTR+MTBF are telling us:
- We can say that in Dec-2013 we had failures every 12 hours that lasted 3.5 hours on average
- We can see that in the last few months we have much more failures (MTBF decrease) and it takes us a lot more time to fix them (MTTR increase).
3. Maintenance hours
Short description: the amount of hours spent on maintenance.
Who uses it (importance): higher management (low), factory management (High), unit management (med)
Description: When looking at maintenance hours we use 2 views:
- The overall number of hours by time: shows us if there is an up trend or a down trend..
- A specific time period (usually a month): Shows us the specific tools that had downtime due to maintenance.
