Our customer owned several Heller Cat 50 taper horizontal CNC milling machines set up for cutting aluminium at high speeds. They received an order to mill cast parts and found the spindles were failing frequently during the production run. The OEM gave them the option of purchasing new spindles with a high price and long lead time. We sat with them and reviewed their process and the spindle issues they were having.
1) The feed rates had to be reduced to get the spindles to last more than a month. This made the cycle times far to long to remain profitable making the part.
2) When we evaluated the spindles we found the retention force on the tool holder was significantly lower than it should be. We found the tool was being pulled out of the taper during cuts. This caused taper damage (bell-mouthing and uneven wear). This also caused damage to the gripper fingers adding to the retention force issues.
3) The taper damage caused tool runout which in turn shortened the life of the tooling. It also caused chatter on the part.
Northland Tool redesigned the spindles drawbar system and brought the drawbar force from 2200 pounds to 4800 pounds. We redesigned the bearing complement to increase the load capabilities in the axial and radial positions.
It has been 3 years since the first conversion of many was done. We have not experienced a single failure since we started repairing the Heller spindles. Cost savings was shown in spindle repair expenditures, tooling life, tool holder life, gripper replacement costs, improved cycle times and machine downtime.
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Catastrophic bearing failure was the main cause of this spindle malfunction
Continue reading to learn how Northland Tool performed this repair and converted a Weiss GHK 176239 spindle from grease-injected to permanent grease lubrication…