Equipment and Maintenance Management
What the exam tests
Expect questions on OEE, downtime classification, preventive and predictive maintenance, work orders, calibration, MTBF, MTTR, and the difference between equipment effectiveness and overall plant effectiveness.
Core rules
- OEE = availability x performance x quality. Availability uses run time versus planned production time; performance compares actual output to ideal output; quality compares good units to total units.
- Planned maintenance and planned shutdowns are usually excluded from planned production time when calculating OEE; unplanned breakdowns reduce availability.
- MTBF = total operating time / number of failures. MTTR = total repair time / number of repairs.
- Preventive maintenance follows time or usage; predictive maintenance follows condition data such as vibration or temperature.
- Calibration status matters because invalid instruments can invalidate quality data.
Worked example
Planned production time is 480 minutes. Unplanned downtime is 48 minutes, so run time is 432 minutes. Ideal cycle time is 30 seconds, output is 720 units, and good units are 684. Availability = 432/480 = 0.90. Performance = (30 x 720)/25,920 = 21,600/25,920 = 0.833. Quality = 684/720 = 0.95. OEE = 0.90 x 0.833 x 0.95 = 0.712, or 71.2%.
Traps
- Putting planned maintenance in unplanned downtime and understating availability.
- Using calendar time instead of planned production time.
- Calling OEE a maintenance metric only; it spans equipment, process, and quality losses.
- Ignoring calibration status when using equipment data for release decisions.