5.3 Predictive Maintenance (PdM)

Predictive Maintenance (PdM) transitions facility management from fixed-schedule replacement to condition-based intervention. While Preventive Maintenance relies on statistical averages (replacing a bearing every 5,000 hours), PdM utilizes real-time data to detect the precursor signatures of failure (vibration, heat, ultrasonic noise). This methodology eliminates unnecessary part replacements and prevents catastrophic machine failures that occur before the scheduled maintenance window.

Vibration Analysis

Rotating assets, specifically reflow oven convection blowers and wave solder impellers, must be monitored for mechanical imbalance, misalignment, or bearing fatigue.

• Metric: Velocity (mm/s RMS) is the standard metric for machines operating between 600 and 12,000 RPM.
• Measurement Points: Sensors must be placed on the bearing housing in the horizontal, vertical, and axial planes.
• Thresholds (ISO 10816-3 Class I):
  • < 2.8 mm/s: Good / Acceptable.
  • 2.8 – 4.5 mm/s: Warning. Increase monitoring frequency to daily.
  • > 4.5 mm/s: Critical. Machine must be scheduled for immediate bearing replacement.
• Mandate: All Reflow Oven convection motors must be measured monthly. A rise in vibration amplitude at 1x RPM indicates imbalance (fan build-up); a rise at non-synchronous frequencies indicates bearing defects.

Infrared Thermography (IR)

Thermal imaging is mandatory for detecting high-resistance connections in electrical panels and mechanical friction in drive systems.

• Electrical Panels: loose connections generate heat due to increased resistance ($P = I^2R$).
  • Delta-T Limit: Any connection showing a temperature rise of >5 C over a reference phase or ambient baseline requires retorquing. A rise of >20 C requires immediate shutdown and component replacement.
• Mechanical Systems:
  • Motors: Housing temperatures exceeding 80 C (or manufacturer rating) indicate winding insulation breakdown or ventilation failure.
  • Gearboxes: Localized hot spots indicate lubrication failure or misalignment.

Ultrasonic Leak Detection

Compressed air and Nitrogen (N2) leaks are often inaudible to the human ear but generate high-frequency turbulence identifiable by ultrasonic detectors.

• Compressed Air: Leaks cause pressure drops that trigger pick-and-place vacuum errors.
  • Mandate: Scan all overhead distribution lines and regulator drops semi-annually.
• Nitrogen (N2): N2 is a significant operational cost. Leaks in the reflow oven plumbing compromise inert atmosphere integrity.
  • Mandate: Scan reflow oven N2 plumbing quarterly. Any leak generating >10 dB over background noise must be tagged and sealed.

Motor Current Analysis

Monitoring the current draw of conveyor motors and pick-and-place heads provides early warning of mechanical binding.

• Baseline: Establish a "Golden Trace" of current draw during a standard cycle.
• Deviation:
  • Elevated Baseline: Indicates friction (lack of lubrication, belt tension too high).
  • Spikes: Indicate jamming or physical obstruction.
• Mandate: Conveyor systems must have "Over-Torque" limits set in the PLC to cut power immediately if current exceeds 120% of nominal load, preventing PCBA crash damage.

Final Checklist

Technology	Asset Class	Monitoring Freq.	Action Threshold
Vibration	Reflow Blowers	Monthly	> 4.5 mm/s RMS
Vibration	Wave Impellers	Monthly	> 4.5 mm/s RMS
Thermography	Electrical Panels	Annually	> 5 C Delta-T
Thermography	Motors/Gearboxes	Quarterly	> 80 C Housing
Ultrasonic	N2/Air Lines	Semi-Annually	> 10 dB Signal
Current	Conveyors	Continuous	> 120% Nominal