Full definition
A time-based or usage-based maintenance strategy that performs scheduled activities at predetermined intervals to maintain equipment in good operating condition and reduce the probability of failure. Activities include: lubrication (regreasing bearings, oil changes), inspection (visual, dimensional, functional checks), adjustment (belt tension, alignment verification, calibration), cleaning (removing contamination, clearing filters), and scheduled replacement of wear items (belts, filters, seals, bearings) before reaching their expected end of life. PM intervals are based on: manufacturer recommendations, operating experience, MTBF data, and regulatory requirements. Per ISO 55000 (asset management) and TPM methodology. A well-structured PM program typically prevents 70-80% of potential failures at a fraction of the cost of corrective maintenance. Key metrics: PM compliance (target >90% — percentage of scheduled PMs completed on time), PM-to-CM ratio (target >80% PM, <20% CM), and mean time between failures (MTBF, should increase with effective PM). PM limitations: some components fail randomly (no wear-out pattern), making time-based replacement wasteful — these are candidates for predictive (condition-based) maintenance instead. The optimal maintenance mix combines PM for wear-out items, PdM for condition-detectable items, and corrective for non-critical run-to-failure items.