TL;DR
Tool changer faults are usually a pocket sensor failure, tool taper contamination, or drawbar pressure fault. Check the drawbar pressure and clean the spindle taper before looking at the magazine sensors.
What you might see
- tool change cycle stops mid-sequence with a fault alarm
- tool remains in spindle after change command
- magazine arm does not advance to the correct pocket
- tool pull force insufficient alarm
Likely causes
Drawbar Belleville spring pack worn reducing clamping force
Spindle taper contaminated with coolant residue preventing proper tool seating
Tool magazine pocket sensor failed causing the changer to lose position
Tool holder retention knob loose or missing
Required tools
- Drawbar force gauge (if available)
- Lint-free cloth and spindle oil
- Retention knob torque wrench
- Multimeter for sensor continuity
- LOTO kit
Safety first
- Lock out the machine before reaching into the tool magazine area. Magazine arms move at high speed without warning.
- Heavy fixturing and large tooling in the tool changer represent crush hazards. Never reach into the magazine travel zone during operation.
- Maintain the correct retention knob torque on all tool holders. Under-torqued retention knobs can cause tool ejection during cutting.
Procedure
- 1
Note the specific fault alarm code from the DMG Mori controller and locate it in the maintenance alarm list.[1]
- 2
Lock out the machine before opening the tool magazine area for any mechanical inspection.
- 3
Inspect the spindle taper for coolant residue, chips, or oil film. Clean with a lint-free cloth and apply a thin coat of spindle oil.[1]
- 4
Verify the retention knob (pull stud) on the suspect tool holder is fully tightened to the specification for the holder taper size.
- 5
Check the drawbar pressure using the machine test feature if available, or measure the tool extraction force with a force gauge. Compare to the DMG Mori specification.
- 6
Inspect the magazine pocket sensor for the failed pocket. Check alignment and electrical connection before replacing.
- 7
After repairs, run a manual tool change cycle on the affected position and confirm the fault does not recur before returning to production.
Sources
DMG Mori DMG Mori DMU / DMC 5-Axis CNC Machining Center general technical documentation, DMG Mori
DMG Mori DMU / DMC machining center maintenance manual, automatic tool changer inspection and fault diagnosis (general)
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