The formula

Unattended time = parts in buffer per machine × cycle time per part.

Cycle time per part = machining time + robot load/unload time (when the machine waits for the robot).

Worked example

• Machining time: 250 s

• Robot load/unload: 38 s → cycle 288 s

• Buffer: 140 blanks shared by 2 machines → 70 per machine

• Unattended time: 70 × 288 s = 20,160 s = 5.6 h

Things that reduce real autonomy

• Gauge-triggered stops when tolerances drift

• Chip build-up on grippers or fixtures

• Tool life shorter than the unattended period

• Coolant level and chip conveyor capacity

Practical advice

Match tool life and chip capacity to the buffer before adding more buffer. A larger drawer system is of little use if a tool wears out after three hours.