END USER: Micro-Tronics Inc., (602) 437-8995, www.micro-tronics.com.
CHALLENGE: Prevent sealed bearings from overheating in a live tooling head.
SOLUTION: A live tooling head with coolant-fed bearings.
SOLUTION PROVIDER: Planet Products Corp., (513) 984-5544, www.planet-products.com.

As live tooling becomes more popular in CNC turning centers, tooling with sealed bearings can pose a challenge for shops that produce parts in high volumes or with long cycle times. Most conventional live tooling designs have sealed bearings in the tool head, which may overheat during continuous use or under heavy loads. This may reduce performance of a precision machine, reduce tool life and result in frequent and costly maintenance issues.

Micro-Tronics Inc., a Tempe, Ariz., machine shop that produces metal valves, bearing races and related products for the aerospace and automotive industries, was facing the challenge of using conventional live tooling with sealed bearings. The shop produces 250 to 1,000 parts with cycle times of more than 30 minutes.

"If a shop produces high-cycle-time or high-volume parts, then thermal growth usually occurs in the tool head," said Mike Thompson, lathe supervisor at Micro-Tronics. "The sealed bearings warm up after 6 to 8 hours."

Thompson noted the occurrence of thermal growth requires offset deviations. "If you are holding really tight tolerances, you have to start moving your offsets around to hold dimensional size," he said.

To avoid such problems, Micro-Tronics acquired a new type of live tooling head for its Puma 300M lathe. The tooling from Planet Products Corp., Cincinnati, has a coolant-fed bearing assembly.

PPC's live tooling design for turret lathes utilizes the continuous flow of coolant to cool and lubricate the tool/workpiece interface. The fluid is directed through the tool head, cooling the bearings. Live tooling with coolant- fed bearings can run at high speeds and long cycle times without the accuracy and failure problems of conventional live tooling with sealed bearings, according to Thompson. "With this design, those bearings are constantly being lubricated with water-based synthetic coolant."

Planet Products' live tooling design for turret lathes has a coolant-fed bearing assembly that prevents the bearings from overheating.

Conversely, conventional live tooling prevents coolant from contacting the bearings. Conventional sealed bearings rely on seal integrity or the lubricant packing to keep bearings operating normally under stressful conditions. If coolant does contact the bearing's grease packing, a sludge forms that hinders bearing functionality and eventually causes failure.

Another benefit Thompson pointed out is that the filtered coolant-fed bearing design keeps metal chips and other contaminants from the bearing assembly. In some cases, contaminants contact the bearings and cause bearing-seal failures.

"However, the real benefit is we can put a cutting tool into production on large orders. We constantly hold tight tolerances without having to make tool offset adjustments," Thompson said. "It reduces cycle time in the long run because I don't have to chase the tool around to hold tolerance."