Glossary · approach
Preventive Maintenance
Scheduled maintenance performed before an asset fails — to avoid unplanned downtime.
PMPlanned Maintenance
Preventive maintenance (PM) is the planned maintenance activity performed before the probability of failure rises above an acceptable level. Three main approaches: (1) Time-based — fixed calendar (e.g. 'every 6 months'), (2) Usage-based — by an operational measure (e.g. 'every 500 hours'), (3) Condition-based (CBM) — real-time decisions from sensor data. The opposite is 'corrective maintenance', which is the repair after a failure. Optimum PM frequency is found through the mathematical balance of the asset's reliability distribution (often Weibull), maintenance cost, and downtime cost.
Örnek
If the bearing on a CNC machine is replaced every 850 operating hours, there's an 85% probability of failure-free operation. At 500 hours, the probability rises to 95% but maintenance cost is high; at 1,200 hours, it drops to 50%. 850 hours is the optimum — the sum of maintenance and downtime cost is minimal.