DMG DMU 80 T Spindle Repair

The DMG DMU 80T is a 5-axis simultaneous CNC machining center.  It can come fitted with this grease lubricated and stator driven spindle capable of running up to 12,000 rpm.

CHALLENGE

Our customer indicated that the spindle was crashed and now had excessive runout.  The HSK tooling taper was visibly damaged and had 12µ runout in assembly incoming and the gripper fingers had damage and wear.  It was also noted that there was very low tool retention force incoming, which could be due to the ejector pin getting displaced.  After disassembly and evaluation, we noted that the drawbar shaft was corroded and had heavy spring wear. One spring was sticking, which would also cause the low pull force.  The front spindle shaft nut was loctited on and the shaft nut/threads had light galling. Lastly, we noted that one o-ring in the front cover was missing and the ceramic surface of the rotary union was chipped, allowing contamination around the encoder sensor and into the drawbar cavity.  No other dimensional deviations were noted for this repair.

SOLUTION

The following actions were performed on this DMG DMU 80 T spindle:

• Clean, inspect overall dimensions
• Grind, chrome plate, and finish grind the HSK 63 taper
• Repair front spindle shaft nut and shaft threads
• Replace drawbar and gripper assembly
• Replace hybrid ceramic bearings, rotary union (both sides), encoder sensor, o-rings, and assembly screws

RESULT

After reassembly of all components, adjusting bearing preload, and undergoing break-in and testing procedures, this spindle passed our final quality inspection before being returned to our customer with a 1-year warranty.