Shifting To A Rapid Rate

For micromachining applications, adding a high-speed, or ultra-high-speed, spindle to a machine tool provides multiple benefits, with a significant reduction in cycle times being a major one. Brian Neale, CoolSpeed product specialist for WTO Inc., noted that one customer recently was consuming about 10 hours to machine a part with thousands of small holes and reduced the cycle time to three to four hours using a Cool- Speed ultra-high-speed spindle. “Think of all the time that’s going to free up.”

The Charlotte, North Carolina, company supplies coolant driven spindles manufactured in Germany, by WTO Werkzeug-Einrichtungen GmbH that operate from 20,000 to 80,000 rpm.

Extending the life for microtools is another key advantage to high-speed machining, Neale said. Microtools are generally considered to be 3.175 mm (1/8″) and smaller. “The smallest tool that I’ve actively tested with a customer is 0.003”.

He explained that it can be challenging to know exactly how a microtool will function, but the “standard physics” for a larger cutting tool does not necessarily apply. “A microtool just doesn’t want to run at a slower speed, so you need all the speed you can get.”

When run at the proper high speed, Neale said it is possible to get two to five times faster cutting speeds and tool life on average with some customers experiencing significantly more than that.

In addition, a small tool can be effective when imparting a fine surface finish, according to Neale, especially when machining complex geometries on a variety of workpiece sizes. “Just because you’re using a small tool doesn’t mean it’s being used on a small part.”

Steve Boucher, engineering manager at GMN USA in Bristol, Connecticut, concurred that achieving a fine surface finish is a major benefit of a high-speed spindle, particularly when grinding. The company offers manual tool change spindles with speeds up to 250,000 rpm, which are primarily for grinding, as well as the UH series manual tool change spindles with a speed up to 120,000 rpm and the HCS series automatic tool change spindles for reaching a speed up to 105,000 rpm when milling. “For grinding, a lot of times the parts are roughed at a slower speed and then users just do the last surface finishing with a very high-speed grinding wheel.”

Microscale grinding wheels are needed for high-speed applications, Boucher added, sometimes as small as 0.5 mm (0.02″). “Not many shops need a 250,000-rpm spindle because in that case they need to also come up with those very small grinding wheels. We have no problem coming up with the speeds, but at that point it’s limited on their tooling.”

He noted that the company’s spindles are also suitable for applications that don’t qualify as micromachining. “You can have a ½” endmill in there and it’s going 40,000 rpm. That’s still considered high-speed milling.”

A manual tool change spindle is oftentimes used in an R&D environment or as the initial choice to determine what the spindle is capable of before getting into production, Boucher said. Then GMN can modify or redesign the spindle to provide an automatic tool change.

Added Accessories

Boucher explained that torque is frequently used at a lower speed and is inversely related to speed, so there is less torque at a higher speed because the speed makes up for the power. “With our permanent magnet motors, or synchronous motors, you have the torque throughout the spectrum.”

GMN USA offers accessories for its high-speed spindles to enhance their operation, including industrial chillers, an electronically controlled lubricator, quills and spindle drives.

Because micromachining and grinding require a very stable spindle, a chiller, such as the Pfannenberg models that the company offers, provides accurate temperature regulation and effective cooling capabilities, Boucher said. Water chillers are crafted to prioritize energy efficiency, lower operational expenses and minimize environmental footprint. “Water is mixed with Glycol to keep the motor in the spindle bearing at a stable temperature to make up for any thermal expansion.”

Because operators need precise, secure and controllable lubricant dosing, especially for thorough bearing lubrication during the startup and shutdown phases, GMN USA provides Prelub lubricators. “Lubrication to the spindle is very precise because it is mostly an air system with droplets of oil within,” Boucher said. “It’s minimal lubrication to the bearing that is required for high speed.”

A quill allows a CNC spindle to reach into the deep, hard-to-finish recesses of a workpiece when grinding and abrasive machining, essentially a telescopic extension of a spindle. Boucher added that quills are usually made of carbide and provide minimal runout and a high level of concentricity.