MTBF
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MTBF (Mean Time Between Failures) measures average equipment reliability by calculating the average operating time between breakdowns.
Definition
MTBF (Mean Time Between Failures) is a reliability metric that measures the average time equipment operates between failures. It is calculated by dividing total operating time by the number of failures in that period. Higher MTBF indicates more reliable equipment. MTBF helps predict maintenance needs, compare equipment reliability, justify improvement investments, and track the effectiveness of TPM initiatives. Combined with MTTR (Mean Time To Repair), MTBF enables availability calculations.
Examples
A CNC machine operated 2,000 hours over six months with 4 breakdowns. MTBF = 2,000 / 4 = 500 hours. After implementing TPM, the next six months showed 2,000 hours with only 2 breakdowns. MTBF improved to 1,000 hours—double the reliability.
Key Points
- MTBF = Total Operating Time / Number of Failures
- Higher MTBF indicates more reliable equipment
- Used for maintenance planning, reliability comparison, and improvement tracking
- Availability = MTBF / (MTBF + MTTR)
Common Misconceptions
MTBF predicts when the next failure will occur. MTBF is an average, not a prediction for individual units. A machine with 500-hour MTBF might fail at 100 hours or run 1,000 hours. Failure timing is probabilistic, not deterministic.
MTBF applies to individual components and whole systems the same way. System MTBF depends on component arrangement (series vs. parallel) and individual component MTBFs. A system with many series components has lower MTBF than its individual parts.