Mitsubishi MV60E Coolant Contamination Spindle Failure



CHALLENGE

Washed-out bearings, contamination, corrosion, damaged components Mitsubishi MV60E, 6000 RPM, grease bearing lubrication, stator driven This exterior of this vertical machining center spindle was corroded and covered with sticky coolant residue when we received it.  It was also apparent that the encoder gear located behind the rear roller bearing had several damaged teeth. Our internal inspection revealed a similar condition inside. The front of the spindle was heavily corroded and the grease had been completely washed out of the front bearing quad set. This led to failure of the #1 front bearing including the phenolic cage having broken and melted. We observed significant wear and corrosion on the gripper (collet) assembly & the rear of the drawbar, which was also bent with runout of >200µ. Our incoming measurement showed very low tool retention force which was not surprising given that the Belleville washers were compressed and most of the grease had been washed out. The tooling taper was pock marked with poor tool contact at the mouth and slightly excessive runout.  This spindle had suffered greatly overall from coolant contamination though the front & back of the spindle, as well as very hard use.

SOLUTION

Despite the significant wear and damage to this spindle, the remedies were relatively uncomplicated. We put the spindle shaft up on one of our Kellenberger grinders to attend to the wear & runout in the tooling taper with a precision kiss grind. We addressed the bend in the rear of the drawbar shaft by straightening it in our machine shop. We then reassembled the spindle with all new bearings, Bellevilles, grippers, encoder gear, o-rings & assembly screws. We ran up the spindle for 4 hours to break in the new bearing grease while checking the thermal & vibration characteristics. Now the spindle will perform as it did when brand new, though we can assume that it has another hard road ahead of it.

DETAILED CAUSE OF FAILURE

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