As live tooling becomes more popular in many CNC turning centers, the use of tooling with sealed bearing performance is becoming a challenge for shops that produce components in high volumes or with lengthy cycle times.
Most common live tooling designs use sealed bearings that may be contaminated or overheat under heavy, repetitive use. This can diminish machining precision, reduce the service life of tools and result in frequent and costly maintenance that compromises productivity.
This article presents two stories, one from Micro-Tronics (Tempe, Ariz.) and another from Buku Performance Products (Gambrills, Md.), in which both companies turned to Planet Products Inc. to solve their problems with live tooling.
“If a shop produces items that are high cycle or high volumes, then thermal growth will usually occur in the tool head,” says Mike Thompson, lathe supervisor at Micro-Tronics Inc., a precision machine shop that produces metal valves and related products for the aerospace and automotive industries.
While using live tools with sealed bearings, Mr. Thompson has experienced thermal growth, causing offset deviations that adversely affected workpiece tolerances. In another instance, metal chips entered and fouled the tool head bearing after the bearing seal had failed.
To avoid such problems, Micro-Tronics recently acquired a unique type of toolholder for each of its new lathes—a toolholder with a coolant-fed, or externally cooled, bearing assembly from Planet Products Inc. Planet Products has developed a live tool design for turret lathe applications that uses a continuous flow of filtered machine coolant to lubricate and cool the bearings, eliminating many of the existing failure modes.
Unlike conventional bearings, coolant-fed bearings do not rely on seal integrity or the lubricant packing to keep bearings operating normally, even under stressful conditions. Instead, the filtered coolant that is used to externally cool and lubricate the live tools and workpieces is directed to flow through the tool, keeping the bearings cool and maintaining accuracy.
Conversely, conventional tooling is designed to prevent coolant from contacting bearings, because in the event that coolant contacts the bearing’s grease packing, a sludge is formed that will hinder bearing functionality and eventually cause failure.
Mr. Thompson says, in some cases when bearing seals fail, foreign objects such as metal shavings from the workpiece can contact the bearing and cause failures. With the externally cooled and lubricated coolant-fed bearing design, this danger is virtually eliminated because the coolant will wash any metal chips or other contaminants away from the bearing assembly.
Over-Speed Live Tooling Heads
Buku Performance Products (Gambrills, Md.), a small business that manufactures aftermarket high-performance components for radio-controlled vehicles, is always looking for ways to improve efficiency.
When Dave Maslar, CEO of Buku, heard that Planet Products offers an over-speed live tooling head for his model of turret lathe, he decided to see if that head could enable Buku’s operation to improve production throughput of its aluminum components. These heads feature a gear-up ratio that allows the tool to spin faster than a turret drive. This increased speed, along with the coolant-fed bearing feature, is advantageous for lathe operations with high-cycle, high-volume requirements, enabling them to process components considerably faster with increased tool service life.
“We compete directly against overseas manufacturers located in lower-cost environments, so production costs are always a concern for us,” Mr. Maslar says.
“Our cycle time was approximately 6 1/2 minutes, and more than 4 of those minutes were holding a 3/32 end mill in machining aluminum and cutting deep slots,” Mr. Maslar says. “The live tool turret on my machine is limited to 5,000 rpm. That was the limiting factor for the time it was taking to produce these components. So, the over-speed appeared to be a good way to address that issue.”
By using the over-speed head, Mr. Maslar was able to reduce cycle time by more than 2 minutes. Tool cutting reliability and accuracy were maintained, even though the cycle time placed a heavy demand on the tool.
“The bearings are running fast, and they are running for a long time,” Mr. Maslar says. “But having the coolant lubricate the bearings eliminated any concerns we could have had regarding overusing the live tool for that amount of time.”
He adds that when bearings are externally lubricated and cooled, as with the Planet Products over-speed tool, the bearings’ tolerances can be tighter, which improves the runout characteristic in the bearing.
There is an upper limit to how tight to make bearings if the tool it’s in will be running for a long time, Mr. Maslar says. Yet, he experienced a significant improvement in runout that he attributes to the active, external cooling and lubrication of the bearings in the tool head.
“That’s a very important result because I’m running a 3/32-inch, three-flute end mill, and the feed-per-revolution is distributed among three cutting teeth,” he says. “Even the slightest bit of runout can cause one tooth to substantially overcut and wear faster, and the tool will fail more quickly than it should. From a tool cost, that may be no big deal, but from a production downtime standpoint, that may be expensive. So far, we’ve not broken one end mill and that reflects cutting times of 20 to 30 hours on a single end mill.”
He adds that while Buku’s operation is cutting aluminum, which is a soft material, shops that are cutting hard materials should have an even greater appreciation for the tool runout improvements.
In both the instances of Micro-Tronics and Buku Performance Products issues, Planet Products’ live tool designs made a difference in the companies’ process efficiencies, which in turn, saves time.