The Myth of "Just Turning It Off"
Flipping the main disconnect switch on a machine tool does not make it safe to work on. Hazardous energy exists in multiple forms beyond electrical. A 500-ton hydraulic press retains thousands of PSI in its accumulators long after the power is cut. A suspended Z-axis on a milling machine holds massive potential kinetic energy that will release if the servomotor brake fails or is mechanically disengaged.
The 6-Step Verification Protocol
- 1. Preparation: Identify all energy sources (Electrical, Pneumatic, Hydraulic, Thermal, Gravity).
- 2. Shutdown: Follow normal machine shutdown sequencing to prevent tool drops or data corruption.
- 3. Isolation: Throw the main disconnects and close physical valves.
- 4. Lockout: Apply physical padlocks to all isolation points. Only the tech holds the key.
- 5. Dissipation: Bleed air lines, dump hydraulic accumulators, and physically block vertical axes (die blocks).
- 6. Verification: Attempt to start the machine to confirm isolation (Try-Out).
Stored Energy Risks
- Capacitors: VFDs and servo amplifiers retain lethal DC bus voltages for up to 15 minutes after power is removed. Always verify with a multimeter before touching bus bars.
- Pneumatics: Air lines often have trapped pressure between the shutoff valve and the cylinder. Use exhaust-type lockout valves.