MTTR stands for mean time to repair, and MTBF stands for mean time between failures. Both are critical key performance indicators (KPIs) in manufacturing.
Mean time to repair is a measurement of the average time required to fix equipment and return it to production-ready status. Mean time between failures tracks the average time equipment runs before failure occurs.
Collecting, understanding and improving these metrics can help evaluate equipment reliability, enhance maintenance effectiveness and reduce failure risk.
In this piece, we’ll break down the basics of MTTR and MTBF, explore their differences, importance, and share practical strategies to improve both metrics.
Understanding MTTR (mean time to repair)
The formula used to calculate MTTR is:
MTTR = Total downtime / Total number of failures over a specified period
Consider a company calculating MTTR for a piece of automotive production equipment over the past year. If the system has failed seven times for a total of 20 hours of downtime, the formula is as follows:
MTTR = 20 hours / 7 repairs = 2.68 hours per repair.
As a general rule, MTTR includes the time from equipment failure to maintenance team notification, the time required to diagnose and fix the issue, and the time required for any post-repair testing or calibration.
Think of MTTR as a measurement of maintenance responsiveness and efficiency. The lower your MTTR, the faster your recovery speed and the higher your uptime.
Several factors influence MTTR, including:
- Machinery age and condition: Older machines and those that have been running 24/7/365 may fail more often and take longer to repair, especially if key components are beginning to fail and original parts are no longer available.
- Technician skills: Highly trained technicians are often capable of identifying issues and repairing machinery more quickly than their newer, less experienced counterparts.
- Spare parts availability: The availability of spare parts can reduce or increase repair time. If companies have spare parts on hand, repairs could take hours at best and a few days at worst. If parts must be acquired from specialty providers, meanwhile, repairs could take weeks.
- Maintenance process quality: The quality of maintenance processes also plays a role in MTTR. Organizations that have proactive maintenance policies in place, such as scheduled maintenance and regular assessment of production line equipment and subsystems, are more likely to detect issues early and take action before systems go down.
Understanding MTBF (mean time between failures)
The MTBF calculation is as follows:
MTBF = Total operating time / Total number of failures over a set period.
For example, if a piece of production line machinery runs for 1,000 hours and has five failures, the MTBF is 200 hours.
MTBF = 1000 hours / 5 failures = 200 hours between failures.
In practice, MTBF is a measure of reliability, or how long a system can run before failure occurs. The higher your MTBF, the fewer failures you encounter and the more reliable your equipment.
It’s worth noting that MTBF can be misleading without context. Consider the example above. If the first failure occurred after 800 hours of use, and subsequent failures occurred every 50 hours thereafter, the result is an average of 200 hours between failures. Analysis of failure patterns, meanwhile, makes it clear that failures are occurring more often, suggesting the need for targeted maintenance.
Multiple factors impact MTBF. They include:
- Machine quality: The quality of parts and other components, such as lubricants, fluids and connectors, can impact MTBF. Lower-quality machines break down more frequently and require more labor-intensive upkeep.
- Preventive maintenance: Preventive maintenance plans can help increase MTBF. For example, if machines are regularly evaluated for fluid leaks, pressure spikes and corroded components, these issues can be addressed before they lead to downtime.
- Operating environment: Operating environments also impact MTBF. Conditions such as excessive heat, dust, or dryness can reduce machine efficiency and accelerate component wear.
- Frequency of use: Both high and low frequencies of use can impact MTBF. Equipment that runs continuously is at risk of failure due to constant strain on its components. Those used occasionally are also at risk; fluids may dry up, and frequent startups/shutdowns can be hard on components.
MTTR vs. MTBF: Key differences
MTTR and MTBF are complementary metrics. Knowing and understanding both can help companies reduce failure risks and improve maintenance efforts.
Put simply, MTTR focuses on repair speed, while MTBF prioritizes reliability and failure frequency. As a result, manufacturers should prioritize lower MTTR and higher MTBF. In combination, they provide a holistic view of equipment performance.
Measuring or optimizing just one of these metrics can lead to operational inefficiencies. If a company prioritizes quick repairs, it could significantly lower its MTTR. If the organization doesn’t address the underlying reasons, these repairs are necessary; however, they may end up with fast maintenance but frequent breakdowns. Tracking MTBF alongside MTTR helps address symptoms and identify root causes of equipment issues.
Measures | Better when | Influencing factors | |
MTTR | Time to repair | Lower | Machine age and condition Technician skills |
MTBF | Time between failures | Higher | Machine quality Operating environment |
Why MTTR and MTBF matter
Measuring MTTR and MTBF can help improve machine uptime, enhance productivity and reduce maintenance costs.
Four benefits highlight the importance of tracking MTTR and MTBF in tandem are:
1. Improved root cause identification: High MTTR and low MTBF may indicate significant problems with machinery. If failures occur more often and take longer to repair, teams may need to take machines offline and find the source of the problem.
Lower MTTR and higher MTBF, meanwhile, may suggest a symptom rather than a root cause. By analyzing the origin of repair issues, teams can uncover insights that can improve MTBF.
2. Increased overall equipment effectiveness (OEE): OEE combines machine availability and performance with output quality to provide a measurement of actual productive time during operational hours. Here is the formula:
OEE = Availability x Performance x Quality
Consider a piece of machinery with an Availability of 0.75, a Performance value of 0.83, and a Quality rating of 0.90.
OEE = 0.75 x 0.83 x 0.90 = 0.56
This value is then multiplied by 100, giving a result of 56%.
Measuring MTTR and MTBF helps pinpoint issues with availability and performance. Even slight increases in these values can significantly impact OEE. For example, if availability in the example above is increased by 0.05, or 5%, the OEE rises to 59.7%.
3. Enhanced maintenance strategies: Using MTTR and MTBF in tandem lets companies design more effective maintenance strategies and make informed decisions. Consider an MTTR that has been trending upward over the last year. By implementing a preventive maintenance strategy that sees technicians regularly evaluate machinery for potential problems, companies can reduce the risk of critical component failures.
4. Reduced downtime: Optimizing MTTR and MTBF reduces total downtime. Lower machine downtime means lower costs and improved asset utilization, both of which contribute to more consistent revenue.
Strategies to lower MTTR
To lower MTTR, start with these strategies:
- Standardize maintenance processes and procedures.
- Stock critical spare parts to reduce waiting time.
- Train technicians on troubleshooting and repair best practices.
- Use computerized maintenance management systems (CMMS) or other digital tools for quick work order assignments and tracking.
- Implement remote monitoring for faster diagnosis before technicians arrive.
Strategies to increase MTBF
To increase MTBF, consider strategies such as:
- Implementing preventive and predictive maintenance schedules.
- Regularly inspecting and replacing worn components before failure.
- Using high-quality parts and lubrication.
- Analyzing failure metrics data to eliminate recurring issues.
- Ensuring that equipment operates within recommended limits, including those for load, speed, temperature, and pressure.
Making the most of MTTR and MTBF
MTTR measures how quickly you recover from downtime, while MTBF measures how often this downtime occurs. In combination, these metrics provide critical visibility for day-to-day operations. By tracking them over time, companies can discover opportunities to lower MTTR and increase MTBF, in turn improving OEE and driving more efficient asset performance.
Making the most of MTTR and MTBF starts with measurement and review: What is your average and total time to repair, and how often do failures occur? Are these failures evenly spaced, or are symptomatic issues causing a failure cluster effect?
Equipped with current and historical data, you can take action. If your MTTR is increasing, you might offer more in-depth training for staff or ensure you have more spare parts on hand. If your MTBF is falling, you could design a preventive maintenance plan that includes more frequent machine checks and regularly scheduled repairs, even if no problems are reported.
Ready to better manage your metrics and reduce equipment failure rates? Contact ATS today for a consultation on improving equipment reliability and reducing downtime. Let’s talk.
